,,goethe',s ,,theory ,,of ,,colours2 ,,translated ,,from ,,the ,,german3 ,,with ,,notes ,,by ,,charles ,,lock ,,eastlake1 ,r4,a41 ,f4,r4,s4 ,cicero varietatem propri in coloribus nasci1 hinc in alienum migrare existimavit4 ,cert non alibi natura copiosius aut majore lascivi opes suas commendavit4 ,metalla1 gemmas1 marmora1 flores1 astra1 omnia denique qu progenuit suis etiam coloribus distinxit2 ut venia debeatur si quis in tam numeros rerum sylv caligaverit4 ,,celio ,,calcagnini4 ,,london3 ,,john ,,murray1 ,,albemarle ,,street4 #ahdj ,,to ,,jeremiah ,,harman1 ,esq4 ,dear ,sir1 ,i dedicate to you the following translation as a testimony of my sincere gratitude and respect2 in doing so1 ,i but follow the example of ,portius1 an ,italian writer1 who inscribed his translation of ,aristotle's ,treatise on ,colours to one of the ,medici4 ,i have the honour to be1 ,dear ,sir1 ,your most obliged and obedient ,servant1 ,c4 ,l4 ,,eastlake4 ,,the ,,translator',s ,,preface4 ,english writers who have spoken of ,goethe's ,doctrine of ,colours1#a have generally confined their remarks to those parts of the work in which he has undertaken to account for the colours of the prismatic spectrum1 and of refraction altogether1 on principles different from the received theory of ,newton4 ,the less questionable merits of the treatise consisting of a well-arranged mass of observations and experiments1 many of which are important and interesting1 have thus been in a great measure overlooked4 ,the translator1 aware of the opposition which the theoretical views alluded to have met with1 intended at first to make a selection of such of the experiments as seem more directly applicable to the theory and practice of painting4 ,finding1 however1 that the alterations this would have involved would have been incompatible with a clear and connected view of the author's statements1 he preferred giving the theory itself entire1 reflecting1 at the same time1 that some scientific readers may be curious to hear the author speak for himself even on the points at issue4 ,in reviewing the history and progress of his opinions and researches1 ,goethe tells us that he first submitted his views to the public in two short essays entitled ,contributions to ,optics4 ,among the circumstances which he supposes were unfavourable to him on that occasion1 he mentions the choice of his title1 observing that by a reference to optics he must have appeared to make pretensions to a knowledge of mathematics1 a science with which he admits he was very imperfectly acquainted4 ,another cause to which he attributes the severe treatment he experienced1 was his having ventured so openly to question the truth of the established theory3 but this last provocation could not be owing to mere inadvertence on his part2 indeed the larger work1 in which he alludes to these circumstances1 is still more remarkable for the violence of his objections to the ,newtonian doctrine4 ,there can be no doubt1 however1 that much of the opposition ,goethe met with was to be attributed to the manner as well as to the substance of his statements4 ,had he contented himself with merely detailing his experiments and showing their application to the laws of chromatic harmony1 leaving it to others to reconcile them as they could with the pre-established system1 or even to doubt in consequence1 the truth of some of the ,newtonian conclusions1 he would have enjoyed the credit he deserved for the accuracy and the utility of his investigations4 ,as it was1 the uncompromising expression of his convictions only exposed him to the resentment or silent neglect of a great portion of the scientific world1 so that for a time he could not even obtain a fair hearing for the less objectionable or rather highly valuable communications contained in his book4 ,a specimen of his manner of alluding to the ,newtonian theory will be seen in the preface4 ,it was quite natural that this spirit should call forth a somewhat vindictive feeling1 and with it not a little uncandid as well as unsparing criticism4 ,the ,doctrine of ,colours met with this reception in ,germany long before it was noticed in ,england1 where a milder and fairer treatment could hardly be expected1 especially at a time when1 owing perhaps to the limited intercourse with the continent1 ,german literature was far less popular than it is at present4 ,this last fact1 it is true1 can be of little importance in the present instance1 for although the change of opinion with regard to the genius of an enlightened nation must be acknowledged to be beneficial1 it is to be hoped there is no fashion in science1 and the translator begs to state once for all1 that in advocating the neglected merits of the ,doctrine of ,colours1 he is far from undertaking to defend its imputed errors4 ,sufficient time has1 however1 now elapsed since the publication of this work 7in #ahaj7 to allow a calmer and more candid examination of its claims4 ,in this more pleasing task ,germany has again for some time led the way1 and many scientific investigators have followed up the hints and observations of ,goethe with a due acknowledgment of the acuteness of his views4#b ,it may require more magnanimity in ,english scientific readers to do justice to the merits of one who was so open and1 in many respects1 it is believed1 so mistaken an opponent of ,newton2 but it must be admitted that the statements of ,goethe contain more useful principles in all that relates to harmony of colour than any that have been derived from the established doctrine4 ,it is no derogation of the more important truths of the ,newtonian theory to say1 that the views it contains seldom appear in a form calculated for direct application to the arts4 ,the principle of contrast1 so universally exhibited in nature1 so apparent in the action and re-action of the eye itself1 is scarcely hinted at4 ,the equal pretensions of seven colours1 as such1 and the fanciful analogies which their assumed proportions could suggest1 have rarely found favour with the votaries of taste1--indeed they have long been abandoned even by scientific authorities4#c ,and here the translator stops3 he is quite aware that the defects which make the ,newtonian theory so little available for sthetic application1 are far from invalidating its more important conclusions in the opinion of most scientific men4 ,in carefully abstaining therefore from any comparison between the two theories in these latter respects1 he may still be permitted to advocate the clearness and fulness of ,goethe's experiments4 ,the ,german philosopher reduces the colours to their origin and simplest elements2 he sees and constantly bears in mind1 and sometimes ably elucidates1 the phenomena of contrast and gradation1 two principles which may be said to make up the artist's world1 and to constitute the chief elements of beauty4 ,these hints occur mostly in what may be called the scientific part of the work4 ,on the other hand1 in the portion expressly devoted to the sthetic application of the doctrine1 the author seems to have made but an inadequate use of his own principles4 ,in that part of the chapter on chemical colours which relates to the colours of plants and animals1 the same genius and originality which are displayed in the ,essays on ,morphology1 and which have secured to ,goethe undisputed rank among the investigators of nature1 are frequently apparent4 ,but one of the most interesting features of ,goethe's theory1 although it cannot be a recommendation in a scientific point of view1 is1 that it contains1 undoubtedly with very great improvements1 the general doctrine of the ancients and of the ,italians at the revival of letters4 ,the translator has endeavoured1 in some notes1 to point out the connexion between this theory and the practice of the ,italian painters4 ,the ,doctrine of ,colours1 as first published in #ahaj1 consists of two volumes in #hvo41 and sixteen plates1 with descriptions1 in #dto4 ,it is divided into three parts1 a didactic1 a controversial1 and an historical part2 the present translation is confined to the first of these1 with such extracts from the other two as seemed necessary1 in fairness to the author1 to explain some of his statements4 ,the polemical and historical parts are frequently alluded to in the preface and elsewhere in the present work1 but it has not been thought advisable to omit these allusions4 ,no alterations whatever seem to have been made by ,goethe in the didactic portion in later editions1 but he subsequently wrote an additional chapter on entoptic colours1 expressing his wish that it might be inserted in the theory itself at a particular place which he points out4 ,the form of this additional essay is1 however1 very different from that of the rest of the work1 and the translator has therefore merely given some extracts from it in the appendix4 ,the polemical portion has been more than once omitted in later editions4 ,in the two first parts the author's statements are arranged numerically1 in the style of ,bacon's ,natural ,history4 ,this1 we are told1 was for the convenience of reference2 but many passages are thus separately numbered which hardly seem to have required it4 ,the same arrangement is1 however1 strictly followed in the translation to facilitate a comparison with the original where it may be desired2 and here the translator observes1 that although he has sometimes permitted himself to make slight alterations1 in order to avoid unnecessary repetition1 or to make the author's meaning clearer1 he feels that an apology may rather be expected from him for having omitted so little4 ,he was scrupulous on this point1 having once determined to translate the whole treatise1 partly1 as before stated1 from a wish to deal fairly with a controversial writer1 and partly because many passages1 not directly bearing on the scientific views1 are still characteristic of ,goethe4 ,the observations which the translator has ventured to add are inserted in the appendix3 these observations are chiefly confined to such of the author's opinions and conclusions as have direct reference to the arts2 they seldom interfere with the scientific propositions1 even where these have been considered most vulnerable4 #a ,farbenlehre--in the present translation generally rendered ,theory of ,colours4 #b ,sixteen years after the appearance of the ,farbenlehre1 ,dr4 ,johannes ,mller devoted a portion of his work1 ,zur vergleichenden ,physiologie des ,gesichtssinnes des ,menschen und der ,thiere1 to the critical examination of ,goethe's theory4 ,in his introductory remarks he expresses himself as follows--,for my own part ,i readily acknowledge that ,i have been greatly indebted to ,goethe's treatise1 and can truly say that without having studied it for some years in connexion with the actual phenomena1 the present work would hardly have been undertaken4 ,i have no hesitation in confessing more particularly that ,i have full faith in ,goethe's statements1 where they are merely descriptive of the phenomena1 and where the author does not enter into explanations involving a decision on the great points of controversy4 ,the names of ,hegel1 ,schelling1 ,seebeck1 ,steffens1 may also be mentioned1 and many others might be added1 as authorities more or less favourable to the ,farbenlehre4 #c ,when ,newton attempted to reckon up the rays of light decomposed by the prism1 says ,sir ,john ,leslie1 and ventured to assign the famous number seven1 he was apparently influenced by some lurking disposition towards mysticism4 ,if any unprejudiced person will fairly repeat the experiment1 he must soon be convinced that the various coloured spaces which paint the spectrum slide into each other by indefinite shadings3 he may name four or five principal colours1 but the subordinate spaces are evidently so multiplied as to be incapable of enumeration4 ,the same illustrious mathematician1 we can hardly doubt1 was betrayed by a passion for analogy1 when he imagined that the primary colours are distributed over the spectrum after the proportions of the diatonic scale of music1 since those intermediate spaces have really no precise and defined limits4--,treatises on ,various ,subjects of ,natural and ,chemical ,philosophy1 p4 #ei4 ,,preface ,,to ,,the ,,first ,,edition ,,of #ahaj4 ,it may naturally be asked whether1 in proposing to treat of colours1 light itself should not first engage our attention3 to this we briefly and frankly answer that since so much has already been said on the subject of light1 it can hardly be desirable to multiply repetitions by again going over the same ground4 ,indeed1 strictly speaking1 it is useless to attempt to express the nature of a thing abstractedly4 ,effects we can perceive1 and a complete history of those effects would1 in fact1 sufficiently define the nature of the thing itself4 ,we should try in vain to describe a man's character1 but let his acts be collected and an idea of the character will be presented to us4 ,the colours are acts of light2 its active and passive modifications3 thus considered we may expect from them some explanation respecting light itself4 ,colours and light1 it is true1 stand in the most intimate relation to each other1 but we should think of both as belonging to nature as a whole1 for it is nature as a whole which manifests itself by their means in an especial manner to the sense of sight4 ,the completeness of nature displays itself to another sense in a similar way4 ,let the eye be closed1 let the sense of hearing be excited1 and from the lightest breath to the wildest din1 from the simplest sound to the highest harmony1 from the most vehement and impassioned cry to the gentlest word of reason1 still it is ,nature that speaks and manifests her presence1 her power1 her pervading life and the vastness of her relations2 so that a blind man to whom the infinite visible is denied1 can still comprehend an infinite vitality by means of another organ4 ,and thus as we descend the scale of being1 ,nature speaks to other senses--to known1 misunderstood1 and unknown senses3 so speaks she with herself and to us in a thousand modes4 ,to the attentive observer she is nowhere dead nor silent2 she has even a secret agent in inflexible matter1 in a metal1 the smallest portions of which tell us what is passing in the entire mass4 ,however manifold1 complicated1 and unintelligible this language may often seem to us1 yet its elements remain ever the same4 ,with light poise and counterpoise1 ,nature oscillates within her prescribed limits1 yet thus arise all the varieties and conditions of the phenomena which are presented to us in space and time4 ,infinitely various are the means by which we become acquainted with these general movements and tendencies3 now as a simple repulsion and attraction1 now as an upsparkling and vanishing light1 as undulation in the air1 as commotion in matter1 as oxydation and de-oxydation2 but always1 uniting or separating1 the great purpose is found to be to excite and promote existence in some form or other4 ,the observers of nature finding1 however1 that this poise and counterpoise are respectively unequal in effect1 have endeavoured to represent such a relation in terms4 ,they have everywhere remarked and spoken of a greater and lesser principle1 an action and resistance1 a doing and suffering1 an advancing and retiring1 a violent and moderating power2 and thus a symbolical language has arisen1 which1 from its close analogy1 may be employed as equivalent to a direct and appropriate terminology4 ,to apply these designations1 this language of ,nature to the subject we have undertaken3 to enrich and amplify this language by means of the theory of colours and the variety of their phenomena1 and thus facilitate the communication of higher theoretical views1 was the principal aim of the present treatise4 ,the work itself is divided into three parts4 ,the first contains the outline of a theory of colours4 ,in this1 the innumerable cases which present themselves to the observer are collected under certain leading phenomena1 according to an arrangement which will be explained in the ,introduction2 and here it may be remarked1 that although we have adhered throughout to experiment1 and throughout considered it as our basis1 yet the theoretical views which led to the arrangement alluded to1 could not but be stated4 ,it is sometimes unreasonably required by persons who do not even themselves attend to such a condition1 that experimental information should be submitted without any connecting theory to the reader or scholar1 who is himself to form his conclusions as he may list4 ,surely the mere inspection of a subject can profit us but little4 ,every act of seeing leads to consideration1 consideration to reflection1 reflection to combination1 and thus it may be said that in every attentive look on nature we already theorise4 ,but in order to guard against the possible abuse of this abstract view1 in order that the practical deductions we look to should be really useful1 we should theorise without forgetting that we are so doing1 we should theorise with mental self-possession1 and1 to use a bold word1 with irony4 ,in the second part#a we examine the ,newtonian theory2 a theory which by its ascendancy and consideration has hitherto impeded a free inquiry into the phenomena of colours4 ,we combat that hypothesis1 for although it is no longer found available1 it still retains a traditional authority in the world4 ,its real relations to its subject will require to be plainly pointed out2 the old errors must be cleared away1 if the theory of colours is not still to remain in the rear of so many other better investigated departments of natural science4 ,since1 however1 this second part of our work may appear somewhat dry as regards its matter1 and perhaps too vehement and excited in its manner1 we may here be permitted to introduce a sort of allegory in a lighter style1 as a prelude to that graver portion1 and as some excuse for the earnestness alluded to4 ,we compare the ,newtonian theory of colours to an old castle1 which was at first constructed by its architect with youthful precipitation2 it was1 however1 gradually enlarged and equipped by him according to the exigencies of time and circumstances1 and moreover was still further fortified and secured in consequence of feuds and hostile demonstrations4 ,the same system was pursued by his successors and heirs3 their increased wants within1 the harassing vigilance of their opponents without1 and various accidents compelled them in some places to build near1 in others in connexion with the fabric1 and thus to extend the original plan4 ,it became necessary to connect all these incongruous parts and additions by the strangest galleries1 halls and passages4 ,all damages1 whether inflicted by the hand of the enemy or the power of time1 were quickly made good4 ,as occasion required1 they deepened the moats1 raised the walls1 and took care there should be no lack of towers1 battlements1 and embrasures4 ,this care and these exertions gave rise to a prejudice in favour of the great importance of the fortress1 and still upheld that prejudice1 although the arts of building and fortification were by this time very much advanced1 and people had learnt to construct much better dwellings and defences in other cases4 ,but the old castle was chiefly held in honour because it had never been taken1 because it had repulsed so many assaults1 had baffled so many hostile operations1 and had always preserved its virgin renown4 ,this renown1 this influence lasts even now3 it occurs to no one that the old castle is become uninhabitable4 ,its great duration1 its costly construction1 are still constantly spoken of4 ,pilgrims wend their way to it2 hasty sketches of it are shown in all schools1 and it is thus recommended to the reverence of susceptible youth4 ,meanwhile1 the building itself is already abandoned2 its only inmates are a few invalids1 who in simple seriousness imagine that they are prepared for war4 ,thus there is no question here respecting a tedious siege or a doubtful war2 so far from it we find this eighth wonder of the world already nodding to its fall as a deserted piece of antiquity1 and begin at once1 without further ceremony1 to dismantle it from gable and roof downwards2 that the sun may at last shine into the old nest of rats and owls1 and exhibit to the eye of the wondering traveller that labyrinthine1 incongruous style of building1 with its scanty1 make-shift contrivances1 the result of accident and emergency1 its intentional artifice and clumsy repairs4 ,such an inspection will1 however1 only be possible when wall after wall1 arch after arch1 is demolished1 the rubbish being at once cleared away as well as it can be4 ,to effect this1 and to level the site where it is possible to do so1 to arrange the materials thus acquired1 so that they can be hereafter again employed for a new building1 is the arduous duty we have undertaken in this ,second ,part4 ,should we succeed1 by a cheerful application of all possible ability and dexterity1 in razing this ,bastille1 and in gaining a free space1 it is thus by no means intended at once to cover the site again and to encumber it with a new structure2 we propose rather to make use of this area for the purpose of passing in review a pleasing and varied series of illustrative figures4 ,the third part is thus devoted to the historical account of early inquirers and investigators4 ,as we before expressed the opinion that the history of an individual displays his character1 so it may here be well affirmed that the history of science is science itself4 ,we cannot clearly be aware of what we possess till we have the means of knowing what others possessed before us4 ,we cannot really and honestly rejoice in the advantages of our own time if we know not how to appreciate the advantages of former periods4 ,but it was impossible to write1 or even to prepare the way for a history of the theory of colours while the ,newtonian theory existed2 for no aristocratic presumption has ever looked down on those who were not of its order1 with such intolerable arrogance as that betrayed by the ,newtonian school in deciding on all that had been done in earlier times and all that was done around it4 ,with disgust and indignation we find ,priestley1 in his ,history of ,optics1 like many before and after him1 dating the success of all researches into the world of colours from the epoch of a decomposed ray of light1 or what pretended to be so2 looking down with a supercilious air on the ancient and less modern inquirers1 who1 after all1 had proceeded quietly in the right road1 and who have transmitted to us observations and thoughts in detail which we can neither arrange better nor conceive more justly4 ,we have a right to expect from one who proposes to give the history of any science1 that he inform us how the phenomena of which it treats were gradually known1 and what was imagined1 conjectured1 assumed1 or thought respecting them4 ,to state all this in due connexion is by no means an easy task2 need we say that to write a history at all is always a hazardous affair2 with the most honest intention there is always a danger of being dishonest2 for in such an undertaking1 a writer tacitly announces at the outset that he means to place some things in light1 others in shade4 ,the author has1 nevertheless1 long derived pleasure from the prosecution of his task3 but as it is the intention only that presents itself to the mind as a whole1 while the execution is generally accomplished portion by portion1 he is compelled to admit that instead of a history he furnishes only materials for one4 ,these materials consist in translations1 extracts1 original and borrowed comments1 hints1 and notes2 a collection1 in short1 which1 if not answering all that is required1 has at least the merit of having been made with earnestness and interest4 ,lastly1 such materials1--not altogether untouched it is true1 but still not exhausted1--may be more satisfactory to the reflecting reader in the state in which they are1 as he can easily combine them according to his own judgment4 ,this third part1 containing the history of the science1 does not1 however1 thus conclude the subject3 a fourth supplementary portion#b is added4 ,this contains a recapitulation or revision2 with a view to which1 chiefly1 the paragraphs are headed numerically4 ,in the execution of a work of this kind some things may be forgotten1 some are of necessity omitted1 so as not to distract the attention1 some can only be arrived at as corollaries1 and others may require to be exemplified and verified3 on all these accounts1 postscripts1 additions and corrections are indispensable4 ,this part contains1 besides1 some detached essays2 for example1 that on the atmospheric colours2 for as these are introduced in the theory itself without any classification1 they are here presented to the mind's eye at one view4 ,again1 if this essay invites the reader to consult ,nature herself1 another is intended to recommend the artificial aids of science by circumstantially describing the apparatus which will in future be necessary to assist researches into the theory of colours4 ,in conclusion1 it only remains to speak of the plates which are added at the end of the work2#c and here we confess we are reminded of that incompleteness and imperfection which the present undertaking has1 in common with all others of its class2 for as a good play can be in fact only half transmitted to writing1 a great part of its effect depending on the scene1 the personal qualities of the actor1 the powers of his voice1 the peculiarities of his gestures1 and even the spirit and favourable humour of the spectators2 so it is1 in a still greater degree1 with a book which treats of the appearances of nature4 ,to be enjoyed1 to be turned to account1 ,nature herself must be present to the reader1 either really1 or by the help of a lively imagination4 ,indeed1 the author should in such cases communicate his observations orally1 exhibiting the phenomena he describes--as a text1 in the first instance1--partly as they appear to us unsought1 partly as they may be presented by contrivance to serve in particular illustration4 ,explanation and description could not then fail to produce a lively impression4 ,the plates which generally accompany works like the present are thus a most inadequate substitute for all this2 a physical phenomenon exhibiting its effects on all sides is not to be arrested in lines nor denoted by a section4 ,no one ever dreams of explaining chemical experiments with figures2 yet it is customary in physical researches nearly allied to these1 because the object is thus found to be in some degree answered4 ,in many cases1 however1 such diagrams represent mere notions2 they are symbolical resources1 hieroglyphic modes of communication1 which by degrees assume the place of the phenomena and of ,nature herself1 and thus rather hinder than promote true knowledge4 ,in the present instance we could not dispense with plates1 but we have endeavoured so to construct them that they may be confidently referred to for the explanation of the didactic and polemical portions4 ,some of these may even be considered as forming part of the apparatus before mentioned4 ,we now therefore refer the reader to the work itself2 first1 only repeating a request which many an author has already made in vain1 and which the modern ,german reader1 especially1 so seldom grants3-- ,si quid novisti rectius istis ,candidus imperti2 si non1 his utere mecum4 #a ,the ,polemical part4 #b ,this preface must have been written before the work was finished1 for at the conclusion of the historical part there is only an apology for the non-appearance of the supplement here alluded to4 #c ,in the present translation the necessary plates accompany the text4 ,,contents ,introduction xxxvii ,,part ,i4 ,,physiological ,,colours4 ,i4 ,effects of ,light and ,darkness on the ,eye ,,ii4 ,effects of ,black and ,white ,objects on the ,eye ,,iii4 ,grey ,surfaces and ,objects ,,iv4 ,dazzling ,colourless ,objects ,v4 ,coloured ,objects ,,vi4 ,coloured ,shadows ,,vii4 ,faint ,lights ,,viii4 ,subjective ,halos ,pathological ,colours--,appendix ,,part ,,ii4 ,,physical ,,colours4 ,,ix4 ,dioptrical ,colours ,x4 ,dioptrical ,colours of the ,first ,class ,,xi4 ,dioptrical ,colours of the ,second ,class--,refraction ,subjective ,experiments ,,xii4 ,refraction without the ,appearance of ,colour ,,xiii4 ,conditions of the ,appearance of ,colour ,,xiv4 ,conditions under which the ,appearance of ,colour increases ,,xv4 ,explanation of the foregoing ,phenomena ,,xvi4 ,decrease of the ,appearance of ,colour ,,xvii4 ,grey ,objects displaced by ,refraction ,,xviii4 ,coloured ,objects displaced by ,refraction ,,xix4 ,achromatism and ,hyperchromatism ,,xx4 ,advantages of ,subjective ,experiments-- ,transition to the ,objective ,objective ,experiments ,,xxi4 ,refraction without the ,appearance of ,colour ,,xxii4 ,conditions of the ,appearance of ,colour ,,xxiii4 ,conditions of the ,increase of ,colour ,,xxiv4 ,explanation of the foregoing ,phenomena ,,xxv4 ,decrease of the ,appearance of ,colour ,,xxvi4 ,grey ,objects ,,xxvii4 ,coloured ,objects ,,xxviii4 ,achromatism and ,hyperchromatism ,,xxix4 ,combination of ,subjective and ,objective ,experiments ,,xxx4 ,transition ,,xxxi4 ,catoptrical ,colours ,,xxxii4 ,paroptical ,colours ,,xxxiii4 ,epoptical ,colours ,,part ,,iii4 ,,chemical ,,colours4 ,,xxxiv4 ,chemical ,contrast ,,xxxv4 ,white ,,xxxvi4 ,black ,,xxxvii4 ,first ,excitation of ,colour ,,xxxviii4 ,augmentation of ,colour ,,xxxix4 ,culmination ,,xl4 ,fluctuation ,,xli4 ,passage through the ,whole ,scale ,,xlii4 ,inversion ,,xliii4 ,fixation ,,xliv4 ,intermixture1 ,real ,,xlv4 ,intermixture1 ,apparent ,,xlvi4 ,communication1 ,actual ,,xlvii4 ,communication1 ,apparent ,,xlviii4 ,extraction ,,xlix4 ,nomenclature ,l4 ,minerals ,,li4 ,plants ,,lii4 ,worms1 ,insects1 ,fishes ,,liii4 ,birds ,,liv4 ,mammalia and ,human ,beings ,,lv4 ,physical and ,chemical ,effects of the ,transmission of ,light through ,coloured ,mediums ,,lvi4 ,chemical ,effect in ,dioptrical ,achromatism ,,part ,,iv4 ,,general ,,characteristics4 ,the ,facility with which ,colour appears ,the ,definite ,nature of ,colour ,combination of the ,two ,principles ,augmentation to ,red ,junction of the ,two ,augmented ,extremes ,completeness the ,result of ,variety in ,colour ,harmony of the ,complete ,state ,facility with which ,colour may be made to tend either to the ,plus or ,minus side ,evanescence of ,colour ,permanence of ,colour ,,part ,v4 ,,relation ,,to ,,other ,,pursuits4 ,relation to ,philosophy ,relation to ,mathematics ,relation to the ,technical ,operations of the ,dyer ,relation to ,physiology and ,pathology ,relation to ,natural ,history ,relation to ,general ,physics ,relation to the ,theory of ,music ,concluding ,observations on ,terminology ,,part ,,vi4 ,,effect ,,of ,,colour ,,with ,,reference ,,to ,,moral ,,associations4 ,yellow ,red-,yellow ,yellow-,red ,blue ,red-,blue ,blue-,red ,red ,green ,completeness and ,harmony ,characteristic ,combinations ,yellow and ,blue ,yellow and ,red ,blue and ,red ,yellow-,red and ,blue-,red ,combinations ,non-,characteristic ,relation of the ,combinations to ,light and ,dark ,considerations derived from the ,evidence of ,experience and ,history sthetic ,influence ,chiaro-,scuro ,tendency to ,colour ,keeping ,colouring ,colour in ,general ,nature ,colour of ,particular ,objects ,characteristic ,colouring ,harmonious ,colouring ,genuine ,tone ,false ,tone ,weak ,colouring ,the ,motley ,dread of ,theory ,ultimate ,aim ,grounds ,pigments ,allegorical1 ,symbolical1 ,mystical ,application of ,colour ,concluding ,observations ,,outline ,,of ,a ,,theory ,,of ,,colours4 ,si vera nostra sunt aut falsa1 erunt talia1 licet nostra per vitam defendimus4 ,post fata nostra pueri qui nunc ludunt nostri judices erunt4 ,,introduction4 ,the desire of knowledge is first stimulated in us when remarkable phenomena attract our attention4 ,in order that this attention be continued1 it is necessary that we should feel some interest in exercising it1 and thus by degrees we become better acquainted with the object of our curiosity4 ,during this process of observation we remark at first only a vast variety which presses indiscriminately on our view2 we are forced to separate1 to distinguish1 and again to combine2 by which means at last a certain order arises which admits of being surveyed with more or less satisfaction4 ,to accomplish this1 only in a certain degree1 in any department1 requires an unremitting and close application2 and we find1 for this reason1 that men prefer substituting a general theoretical view1 or some system of explanation1 for the facts themselves1 instead of taking the trouble to make themselves first acquainted with cases in detail and then constructing a whole4 ,the attempt to describe and class the phenomena of colours has been only twice made3 first by ,theophrastus1#a and in modern times by ,boyle4 ,the pretensions of the present essay to the third place will hardly be disputed4 ,our historical survey enters into further details4 ,here we merely observe that in the last century such a classification was not to be thought of1 because ,newton had based his hypothesis on a phenomenon exhibited in a complicated and secondary state2 and to this the other cases that forced themselves on the attention were contrived to be referred1 when they could not be passed over in silence2 just as an astronomer would do1 if from whim he were to place the moon in the centre of our system2 he would be compelled to make the earth1 sun1 and planets revolve round the lesser body1 and be forced to disguise and gloss over the error of his first assumption by ingenious calculations and plausible statements4 ,in our prefatory observations we assumed the reader to be acquainted with what was known respecting light2 here we assume the same with regard to the eye4 ,we observed that all nature manifests itself by means of colours to the sense of sight4 ,we now assert1 extraordinary as it may in some degree appear1 that the eye sees no form1 inasmuch as light1 shade1 and colour together constitute that which to our vision distinguishes object from object1 and the parts of an object from each other4 ,from these three1 light1 shade1 and colour1 we construct the visible world1 and thus1 at the same time1 make painting possible1 an art which has the power of producing on a flat surface a much more perfect visible world than the actual one can be4 ,the eye may be said to owe its existence to light1 which calls forth1 as it were1 a sense that is akin to itself2 the eye1 in short1 is formed with reference to light1 to be fit for the action of light2 the light it contains corresponding with the light without4 ,we are here reminded of a significant adage in constant use with the ancient ,ionian school--,like is only known by ,like2 and again1 of the words of an old mystic writer1 which may be thus rendered1 ,if the eye were not sunny1 how could we perceive light8 ,if ,god's own strength lived not in us1 how could we delight in ,divine things8 ,this immediate affinity between light and the eye will be denied by none2 to consider them as identical in substance is less easy to comprehend4 ,it will be more intelligible to assert that a dormant light resides in the eye1 and that it may be excited by the slightest cause from within or from without4 ,in darkness we can1 by an effort of imagination1 call up the brightest images2 in dreams objects appear to us as in broad daylight2 awake1 the slightest external action of light is perceptible1 and if the organ suffers an actual shock1 light and colours spring forth4 ,here1 however1 those who are wont to proceed according to a certain method1 may perhaps observe that as yet we have not decidedly explained what colour is4 ,this question1 like the definition of light and the eye1 we would for the present evade1 and would appeal to our inquiry itself1 where we have circumstantially shown how colour is produced4 ,we have only therefore to repeat that colour is a law of nature in relation with the sense of sight4 ,we must assume1 too1 that every one has this sense1 that every one knows the operation of nature on it1 for to a blind man it would be impossible to speak of colours4 ,that we may not1 however1 appear too anxious to shun such an explanation1 we would restate what has been said as follows3 colour is an elementary phenomenon in nature adapted to the sense of vision2 a phenomenon which1 like all others1 exhibits itself by separation and contrast1 by commixture and union1 by augmentation and neutralization1 by communication and dissolution3 under these general terms its nature may be best comprehended4 ,we do not press this mode of stating the subject on any one4 ,those who1 like ourselves1 find it convenient1 will readily adopt it2 but we have no desire to enter the lists hereafter in its defence4 ,from time immemorial it has been dangerous to treat of colour2 so much so1 that one of our predecessors ventured on a certain occasion to say1 ,the ox becomes furious if a red cloth is shown to him2 but the philosopher1 who speaks of colour only in a general way1 begins to rave4 ,nevertheless1 if we are to proceed to give some account of our work1 to which we have appealed1 we must begin by explaining how we have classed the different conditions under which colour is produced4 ,we found three modes in which it appears2 three classes of colours1 or rather three exhibitions of them all4 ,the distinctions of these classes are easily expressed4 ,thus1 in the first instance1 we considered colours1 as far as they may be said to belong to the eye itself1 and to depend on an action and re-action of the organ2 next1 they attracted our attention as perceived in1 or by means of1 colourless mediums2 and lastly1 where we could consider them as belonging to particular substances4 ,we have denominated the first1 physiological1 the second1 physical1 the third1 chemical colours4 ,the first are fleeting and not to be arrested2 the next are passing1 but still for a while enduring2 the last may be made permanent for any length of time4 ,having separated these classes and kept them as distinct as possible1 with a view to a clear1 didactic exposition1 we have been enabled at the same time to exhibit them in an unbroken series1 to connect the fleeting with the somewhat more enduring1 and these again with the permanent hues2 and thus1 after having carefully attended to a distinct classification in the first instance1 to do away with it again when a larger view was desirable4 ,in a fourth division of our work we have therefore treated generally what was previously detailed under various particular conditions1 and have thus1 in fact1 given a sketch for a future theory of colours4 ,we will here only anticipate our statements so far as to observe1 that light and darkness1 brightness and obscurity1 or if a more general expression is preferred1 light and its absence1 are necessary to the production of colour4 ,next to the light1 a colour appears which we call yellow2 another appears next to the darkness1 which we name blue4 ,when these1 in their purest state1 are so mixed that they are exactly equal1 they produce a third colour called green4 ,each of the two first-named colours can however of itself produce a new tint by being condensed or darkened4 ,they thus acquire a reddish appearance which can be increased to so great a degree that the original blue or yellow is hardly to be recognised in it3 but the intensest and purest red1 especially in physical cases1 is produced when the two extremes of the yellow-red and blue-red are united4 ,this is the actual state of the appearance and generation of colours4 ,but we can also assume an existing red in addition to the definite existing blue and yellow1 and we can produce contrariwise1 by mixing1 what we directly produced by augmentation or deepening4 ,with these three or six colours1 which may be conveniently included in a circle1 the elementary doctrine of colours is alone concerned4 ,all other modifications1 which may be extended to infinity1 have reference more to the application1--have reference to the technical operations of the painter and dyer1 and the various purposes of artificial life4 ,to point out another general quality1 we may observe that colours throughout are to be considered as half-lights1 as half-shadows1 on which account if they are so mixed as reciprocally to destroy their specific hues1 a shadowy tint1 a grey1 is produced4 ,in the fifth division of our inquiry we had proposed to point out the relations in which we should wish our doctrine of colours to stand to other pursuits4 ,important as this part of our work is1 it is perhaps on this very account not so successful as we could wish4 ,yet when we reflect that strictly speaking these relations cannot be described before they exist1 we may console ourselves if we have in some degree failed in endeavouring for the first time to define them4 ,for undoubtedly we should first wait to see how those whom we have endeavoured to serve1 to whom we have intended to make an agreeable and useful offering1 how such persons1 we say1 will accept the result of our utmost exertion3 whether they will adopt it1 whether they will make use of it and follow it up1 or whether they will repel1 reject1 and suffer it to remain unassisted and neglected4 ,meanwhile1 we venture to express what we believe and hope4 ,from the philosopher we believe we merit thanks for having traced the phenomena of colours to their first sources1 to the circumstances under which they simply appear and are1 and beyond which no further explanation respecting them is possible4 ,it will1 besides1 be gratifying to him that we have arranged the appearances described in a form that admits of being easily surveyed1 even should he not altogether approve of the arrangement itself4 ,the medical practitioner1 especially him whose study it is to watch over the organ of sight1 to preserve it1 to assist its defects and to cure its disorders1 we reckon to make especially our friend4 ,in the chapter on the physiological colours1 in the ,appendix relating to those that are more strictly pathological1 he will find himself quite in his own province4 ,we are not without hopes of seeing the physiological phenomena1--a hitherto neglected1 and1 we may add1 most important branch of the theory of colours1--completely investigated through the exertions of those individuals who in our own times are treating this department with success4 ,the investigator of nature should receive us cordially1 since we enable him to exhibit the doctrine of colours in the series of other elementary phenomena1 and at the same time enable him to make use of a corresponding nomenclature1 nay1 almost the same words and designations as under the other rubrics4 ,it is true we give him rather more trouble as a teacher1 for the chapter of colours is not now to be dismissed as heretofore with a few paragraphs and experiments2 nor will the scholar submit to be so scantily entertained as he has hitherto been1 without murmuring4 ,on the other hand1 an advantage will afterwards arise out of this3 for if the ,newtonian doctrine was easily learnt1 insurmountable difficulties presented themselves in its application4 ,our theory is perhaps more difficult to comprehend1 but once known1 all is accomplished1 for it carries its application along with it4 ,the chemist who looks upon colours as indications by which he may detect the more secret properties of material things1 has hitherto found much inconvenience in the denomination and description of colours2 nay1 some have been induced after closer and nicer examination to look upon colour as an uncertain and fallacious criterion in chemical operations4 ,yet we hope by means of our arrangement and the nomenclature before alluded to1 to bring colour again into credit1 and to awaken the conviction that a progressive1 augmenting1 mutable quality1 a quality which admits of alteration even to inversion1 is not fallacious1 but rather calculated to bring to light the most delicate operations of nature4 ,in looking a little further round us1 we are not without fears that we may fail to satisfy another class of scientific men4 ,by an extraordinary combination of circumstances the theory of colours has been drawn into the province and before the tribunal of the mathematician1 a tribunal to which it cannot be said to be amenable4 ,this was owing to its affinity with the other laws of vision which the mathematician was legitimately called upon to treat4 ,it was owing1 again1 to another circumstance3 a great mathematician had investigated the theory of colours1 and having been mistaken in his observations as an experimentalist1 he employed the whole force of his talent to give consistency to this mistake4 ,were both these circumstances considered1 all misunderstanding would presently be removed1 and the mathematician would willingly co-operate with us1 especially in the physical department of the theory4 ,to the practical man1 to the dyer1 on the other hand1 our labour must be altogether acceptable2 for it was precisely those who reflected on the facts resulting from the operations of dyeing who were the least satisfied with the old theory3 they were the first who perceived the insufficiency of the ,newtonian doctrine4 ,the conclusions of men are very different according to the mode in which they approach a science or branch of knowledge2 from which side1 through which door they enter4 ,the literally practical man1 the manufacturer1 whose attention is constantly and forcibly called to the facts which occur under his eye1 who experiences benefit or detriment from the application of his convictions1 to whom loss of time and money is not indifferent1 who is desirous of advancing1 who aims at equalling or surpassing what others have accomplished1--such a person feels the unsoundness and erroneousness of a theory much sooner than the man of letters1 in whose eyes words consecrated by authority are at last equivalent to solid coin2 than the mathematician1 whose formula always remains infallible1 even although the foundation on which it is constructed may not square with it4 ,again1 to carry on the figure before employed1 in entering this theory from the side of painting1 from the side of sthetic#b colouring generally1 we shall be found to have accomplished a most thank-worthy office for the artist4 ,in the sixth part we have endeavoured to define the effects of colour as addressed at once to the eye and mind1 with a view to making them more available for the purposes of art4 ,although much in this portion1 and indeed throughout1 has been suffered to remain as a sketch1 it should be remembered that all theory can in strictness only point out leading principles1 under the guidance of which1 practice may proceed with vigour and be enabled to attain legitimate results4 #a ,the treatise to which the author alludes in more generally ascribed to ,aristotle4--,t4 #b sthetic--belonging to taste as mere internal sense1 from 1 to feel2 the word was first used by ,wolf4--,t4 ,,part ,i4 ,,physiological ,,colours4 #a4 ,we naturally place these colours first1 because they belong altogether1 or in a great degree1 to the subject#a--to the eye itself4 ,they are the foundation of the whole doctrine1 and open to our view the chromatic harmony on which so much difference of opinion has existed4 ,they have been hitherto looked upon as extrinsic and casual1 as illusion and infirmity3 their appearances have been known from ancient date2 but1 as they were too evanescent to be arrested1 they were banished into the region of phantoms1 and under this idea have been very variously described4 #b4 ,thus they are called colores adventicii by ,boyle2 imaginarii and phantastici by ,rizetti2 by ,buffon1 couleurs accidentelles2 by ,scherfer1 scheinfarben 7apparent colours72 ocular illusions and deceptions of sight by many2 by ,hamberger1 vitia fugitiva2 by ,darwin1 ocular spectra4 #c4 ,we have called them physiological because they belong to the eye in a healthy state2 because we consider them as the necessary conditions of vision2 the lively alternating action of which1 with reference to external objects and a principle within it1 is thus plainly indicated4 #d4 ,to these we subjoin the pathological colours1 which1 like all deviations from a constant law1 afford a more complete insight into the nature of the physiological colours4 ,,effects ,,of ,,light ,,and ,,darkness ,,on ,,the ,,eye4 #e4 ,the retina1 after being acted upon by light or darkness1 is found to be in two different states1 which are entirely opposed to each other4 #f4 ,if we keep the eyes open in a totally dark place1 a certain sense of privation is experienced4 ,the organ is abandoned to itself2 it retires into itself4 ,that stimulating and grateful contact is wanting by means of which it is connected with the external world1 and becomes part of a whole4 #g4 ,if we look on a white1 strongly illumined surface1 the eye is dazzled1 and for a time is incapable of distinguishing objects moderately lighted4 #h4 ,the whole of the retina is acted on in each of these extreme states1 and thus we can only experience one of these effects at a time4 ,in the one case 7#f7 we found the organ in the utmost relaxation and susceptibility2 in the other 7#g7 in an overstrained state1 and scarcely susceptible at all4 #i4 ,if we pass suddenly from the one state to the other1 even without supposing these to be the extremes1 but only1 perhaps1 a change from bright to dusky1 the difference is remarkable1 and we find that the effects last for some time4 #aj4 ,in passing from bright daylight to a dusky place we distinguish nothing at first3 by degrees the eye recovers its susceptibility2 strong eyes sooner than weak ones2 the former in a minute1 while the latter may require seven or eight minutes4 #aa4 ,the fact that the eye is not susceptible to faint impressions of light1 if we pass from light to comparative darkness1 has led to curious mistakes in scientific observations4 ,thus an observer1 whose eyes required some time to recover their tone1 was long under the impression that rotten wood did not emit light at noon-day1 even in a dark room4 ,the fact was1 he did not see the faint light1 because he was in the habit of passing from bright sunshine to the dark room1 and only subsequently remained so long there that the eye had time to recover itself4 ,the same may have happened to ,doctor ,wall1 who1 in the daytime1 even in a dark room1 could hardly perceive the electric light of amber4 ,our not seeing the stars by day1 as well as the improved appearance of pictures seen through a double tube1 is also to be attributed to the same cause4 #ab4 ,if we pass from a totally dark place to one illumined by the sun1 we are dazzled4 ,in coming from a lesser degree of darkness to light that is not dazzling1 we perceive all objects clearer and better3 hence eyes that have been in a state of repose are in all cases better able to perceive moderately distinct appearances4 ,prisoners who have been long confined in darkness acquire so great a susceptibility of the retina1 that even in the dark 7probably a darkness very slightly illumined7 they can still distinguish objects4 #ac4 ,in the act which we call seeing1 the retina is at one and the same time in different and even opposite states4 ,the greatest brightness1 short of dazzling1 acts near the greatest darkness4 ,in this state we at once perceive all the intermediate gradations of chiaro-scuro1 and all the varieties of hues4 #ad4 ,we will proceed in due order to consider and examine these elements of the visible world1 as well as the relation in which the organ itself stands to them1 and for this purpose we take the simplest objects4 #a ,the ,german distinction between subject and object is so generally understood and adopted1 that it is hardly necessary to explain that the subject is the individual1 in this case the beholder2 the object1 all that is without him4--,t4 ,,ii4 ,,effects ,,of ,,black ,,and ,,white ,,objects ,,on ,,the ,,eye4 #ae4 ,in the same manner as the retina generally is affected by brightness and darkness1 so it is affected by single bright or dark objects4 ,if light and dark produce different results on the whole retina1 so black and white objects seen at the same time produce the same states together which light and dark occasioned in succession4 #af4 ,a dark object appears smaller than a bright one of the same size4 ,let a white disk be placed on a black ground1 and a black disk on a white ground1 both being exactly similar in size2 let them be seen together at some distance1 and we shall pronounce the last to be about a fifth part smaller than the other4 ,if the black circle be made larger by so much1 they will appear equal4#a #ag4 ,thus ,tycho de ,brahe remarked that the moon in conjunction 7the darker state7 appears about a fifth part smaller than when in opposition 7the bright full state74 ,the first crescent appears to belong to a larger disk than the remaining dark portion1 which can sometimes be distinguished at the period of the new moon4 ,black dresses make people appear smaller than light ones4 ,lights seen behind an edge make an apparent notch in it4 ,a ruler1 behind which the flame of a light just appears1 seems to us indented4 ,the rising or setting sun appears to make a notch in the horizon4 ,illustration #ah4 ,black1 as the equivalent of darkness1 leaves the organ in a state of repose2 white1 as the representative of light1 excites it4 ,we may1 perhaps1 conclude from the above experiment 7#af7 that the unexcited retina1 if left to itself1 is drawn together1 and occupies a less space than in its active state1 produced by the excitement of light4 ,hence ,kepler says very beautifully3 ,certum est vel in retin causs pictur1 vel in spiritibus causs impressionis1 exsistere dilatationem lucidorum4--,paralip4 in ,vitellionem1 p4 #bbj4 ,scherfer expresses a similar conjecture4--,note ,a4 #ai4 ,however this may be1 both impressions derived from such objects remain in the organ itself1 and last for some time1 even when the external cause is removed4 ,in ordinary experience we scarcely notice this1 for objects are seldom presented to us which are very strongly relieved from each other1 and we avoid looking at those appearances that dazzle the sight4 ,in glancing from one object to another1 the succession of images appears to us distinct2 we are not aware that some portion of the impression derived from the object first contemplated passes to that which is next looked at4 #bj4 ,if in the morning1 on waking1 when the eye is very susceptible1 we look intently at the bars of a window relieved against the dawning sky1 and then shut our eyes or look towards a totally dark place1 we shall see a dark cross on a light ground before us for some time4 #ba4 ,every image occupies a certain space on the retina1 and of course a greater or less space in proportion as the object is seen near or at a distance4 ,if we shut the eyes immediately after looking at the sun we shall be surprised to find how small the image it leaves appears4 #bb4 ,if1 on the other hand1 we turn the open eye towards the side of a room1 and consider the visionary image in relation to other objects1 we shall always see it larger in proportion to the distance of the surface on which it is thrown4 ,this is easily explained by the laws of perspective1 according to which a small object near covers a great one at a distance4 #bc4 ,the duration of these visionary impressions varies with the powers or structure of the eye in different individuals1 just as the time necessary for the recovery of the tone of the retina varies in passing from brightness to darkness 7#aj73 it can be measured by minutes and seconds1 indeed much more exactly than it could formerly have been by causing a lighted linstock to revolve rapidly1 so as to appear a circle4--,note ,b4 #bd4 ,but the force with which an impinging light impresses the eye is especially worthy of attention4 ,the image of the sun lasts longest2 other objects1 of various degrees of brightness1 leave the traces of their appearance on the eye for a proportionate time4 #be4 ,these images disappear by degrees1 and diminish at once in distinctness and in size4 #bf4 ,they are reduced from the contour inwards1 and the impression on some persons has been that in square images the angles become gradually blunted till at last a diminished round image floats before the eye4 #bg4 ,such an image1 when its impression is no more observable1 can1 immediately after1 be again revived on the retina by opening and shutting the eye1 thus alternately exciting and resting it4 #bh4 ,images may remain on the retina in morbid affections of the eye for fourteen1 seventeen minutes1 or even longer4 ,this indicates extreme weakness of the organ1 its inability to recover itself2 while visions of persons or things which are the objects of love or aversion indicate the connexion between sense and thought4 #bi4 ,if1 while the image of the window-bars before mentioned lasts1 we look upon a light grey surface1 the cross will then appear light and the panes dark4 ,in the first case 7#bj7 the image was like the original picture1 so that the visionary impression also could continue unchanged2 but in the present instance our attention is excited by a contrary effect being produced4 ,various examples have been given by observers of nature4 #cj4 ,the scientific men who made observations in the ,cordilleras saw a bright appearance round the shadows of their heads on some clouds4 ,this example is a case in point2 for1 while they fixed their eyes on the dark shadow1 and at the same time moved from the spot1 the compensatory light image appeared to float round the real dark one4 ,if we look at a black disk on a light grey surface1 we shall presently1 by changing the direction of the eyes in the slightest degree1 see a bright halo floating round the dark circle4 ,a similar circumstance happened to myself3 for while1 as ,i sat in the open air1 ,i was talking to a man who stood at a little distance from me relieved on a grey sky1 it appeared to me1 as ,i slightly altered the direction of my eyes1 after having for some time looked fixedly at him1 that his head was encircled with a dazzling light4 ,in the same way probably might be explained the circumstance that persons crossing dewy meadows at sunrise see a brightness round each other's heads#b2 the brightness in this case may be also iridescent1 as the phenomena of refraction come into the account4 ,thus again it has been asserted that the shadows of a balloon thrown on clouds were bordered with bright and somewhat variegated circles4 ,beccaria made use of a paper kite in some experiments on electricity4 ,round this kite appeared a small shining cloud varying in size2 the same brightness was even observed round part of the string4 ,sometimes it disappeared1 and if the kite moved faster the light appeared to float to and fro for a few moments on the place before occupied4 ,this appearance1 which could not be explained by those who observed it at the time1 was the image which the eye retained of the kite relieved as a dark mass on a bright sky2 that image being changed into a light mass on a comparatively dark background4 ,in optical and especially in chromatic experiments1 where the observer has to do with bright lights whether colourless or coloured1 great care should be taken that the spectrum which the eye retains in consequence of a previous observation does not mix with the succeeding one1 and thus affect the distinctness and purity of the impression4 #ca4 ,these appearances have been explained as follows3 ,that portion of the retina on which the dark cross 7#bi7 was impressed is to be considered in a state of repose and susceptibility4 ,on this portion therefore the moderately light surface acted in a more lively manner than on the rest of the retina1 which had just been impressed with the light through the panes1 and which1 having thus been excited by a much stronger brightness1 could only view the grey surface as a dark4 #cb4 ,this mode of explanation appears sufficient for the cases in question1 but1 in the consideration of phenomena hereafter to be adduced1 we are forced to trace the effects to higher sources4 #cc4 ,the eye after sleep exhibits its vital elasticity more especially by its tendency to alternate its impressions1 which in the simplest form change from dark to light1 and from light to dark4 ,the eye cannot for a moment remain in a particular state determined by the object it looks upon4 ,on the contrary1 it is forced to a sort of opposition1 which1 in contrasting extreme with extreme1 intermediate degree with intermediate degree1 at the same time combines these opposite impressions1 and thus ever tends to a whole1 whether the impressions are successive1 or simultaneous and confined to one image4 #cd4 ,perhaps the peculiarly grateful sensation which we experience in looking at the skilfully treated chiaro-scuro of colourless pictures and similar works of art arises chiefly from the simultaneous impression of a whole1 which by the organ itself is sought1 rather than arrived at1 in succession1 and which1 whatever may be the result1 can never be arrested4 #a ,plate #a4 fig4 #a4 #b ,see the ,life of ,benvenuto ,cellini1 vol4 i4 p4 #dec4 ,milan edition1 #ahjf4--,t4 ,,iii4 ,,grey ,,surfaces ,,and ,,objects4 #ce4 ,a moderate light is essential to many chromatic experiments4 ,this can be presently obtained by surfaces more or less grey1 and thus we have at once to make ourselves acquainted with this simplest kind of middle tint1 with regard to which it is hardly necessary to observe1 that in many cases a white surface in shadow1 or in a low light1 may be considered equivalent to a grey4 #cf4 ,since a grey surface is intermediate between brightness and darkness1 it admits of our illustrating a phenomenon before described 7#bi7 by an easy experiment4 #cg4 ,let a black object be held before a grey surface1 and let the spectator1 after looking steadfastly at it1 keep his eyes unmoved while it is taken away3 the space it occupied appears much lighter4 ,let a white object be held up in the same manner3 on taking it away the space it occupied will appear much darker than the rest of the surface4 ,let the spectator in both cases turn his eyes this way and that on the surface1 the visionary images will move in like manner4 #ch4 ,a grey object on a black ground appears much brighter than the same object on a white ground4 ,if both comparisons are seen together the spectator can hardly persuade himself that the two greys are identical4 ,we believe this again to be a proof of the great excitability of the retina1 and of the silent resistance which every vital principle is forced to exhibit when any definite or immutable state is presented to it4 ,thus inspiration already presupposes expiration2 thus every systole its diastole4 ,it is the universal formula of life which manifests itself in this as in all other cases4 ,when darkness is presented to the eye it demands brightness1 and vice vers3 it shows its vital energy1 its fitness to receive the impression of the object1 precisely by spontaneously tending to an opposite state4 ,,iv4 ,,dazzling ,,colourless ,,objects4 #ci4 ,if we look at a dazzling1 altogether colourless object1 it makes a strong lasting impression1 and its after-vision is accompanied by an appearance of colour4 #dj4 ,let a room be made as dark as possible2 let there be a circular opening in the window-shutter about three inches in diameter1 which may be closed or not at pleasure4 ,the sun being suffered to shine through this on a white surface1 let the spectator from some little distance fix his eyes on the bright circle thus admitted4 ,the hole being then closed1 let him look towards the darkest part of the room2 a circular image will now be seen to float before him4 ,the middle of this circle will appear bright1 colourless1 or somewhat yellow1 but the border will at the same moment appear red4 ,after a time this red1 increasing towards the centre1 covers the whole circle1 and at last the bright central point4 ,no sooner1 however1 is the whole circle red than the edge begins to be blue1 and the blue gradually encroaches inwards on the red4 ,when the whole is blue the edge becomes dark and colourless4 ,this darker edge again slowly encroaches on the blue till the whole circle appears colourless4 ,the image then becomes gradually fainter1 and at the same time diminishes in size4 ,here again we see how the retina recovers itself by a succession of vibrations after the powerful external impression it received4 7#be1 #bf47 #da4 ,by several repetitions similar in result1 ,i found the comparative duration of these appearances in my own case to be as follows3-- ,i looked on the bright circle five seconds1 and then1 having closed the aperture1 saw the coloured visionary circle floating before me4 ,after thirteen seconds it was altogether red2 twenty-nine seconds next elapsed till the whole was blue1 and forty-eight seconds till it appeared colourless4 ,by shutting and opening the eye ,i constantly revived the image1 so that it did not quite disappear till seven minutes had elapsed4 ,future observers may find these periods shorter or longer as their eyes may be stronger or weaker 7#bc71 but it would be very remarkable if1 notwithstanding such variations1 a corresponding proportion as to relative duration should be found to exist4 #db4 ,but this remarkable phenomenon no sooner excites our attention than we observe a new modification of it4 ,if we receive the impression of the bright circle as before1 and then look on a light grey surface in a moderately lighted room1 an image again floats before us2 but in this instance a dark one3 by degrees it is encircled by a green border that gradually spreads inwards over the whole circle1 as the red did in the former instance4 ,as soon as this has taken place a dingy yellow appears1 and1 filling the space as the blue did before1 is finally lost in a negative shade4 #dc4 ,these two experiments may be combined by placing a black and a white plane surface next each other in a moderately lighted room1 and then looking alternately on one and the other as long as the impression of the light circle lasts3 the spectator will then perceive at first a red and green image alternately1 and afterwards the other changes4 ,after a little practice the two opposite colours may be perceived at once1 by causing the floating image to fall on the junction of the two planes4 ,this can be more conveniently done if the planes are at some distance1 for the spectrum then appears larger4 #dd4 ,i happened to be in a forge towards evening at the moment when a glowing mass of iron was placed on the anvil2 ,i had fixed my eyes steadfastly on it1 and1 turning round1 ,i looked accidentally into an open coal-shed3 a large red image now floated before my eyes1 and1 as ,i turned them from the dark opening to the light boards of which the shed was constructed1 the image appeared half green1 half red1 according as it had a lighter or darker ground behind it4 ,i did not at that time take notice of the subsequent changes of this appearance4 #de4 ,the after-vision occasioned by a total dazzling of the retina corresponds with that of a circumscribed bright object4 ,the red colour seen by persons who are dazzled with snow belongs to this class of phenomena1 as well as the singularly beautiful green colour which dark objects seem to wear after looking long on white paper in the sun4 ,the details of such experiments may be investigated hereafter by those whose young eyes are capable of enduring such trials further for the sake of science4 #df4 ,with these examples we may also class the black letters which in the evening light appear red4 ,perhaps we might insert under the same category the story that drops of blood appeared on the table at which ,henry ,,iv4 of ,france had seated himself with the ,duc de ,guise to play at dice4 ,v4 ,,coloured ,,objects4 #dg4 ,we have hitherto seen the physiological colours displayed in the after-vision of colourless bright objects1 and also in the after-vision of general colourless brightness2 we shall now find analogous appearances if a given colour be presented to the eye3 in considering this1 all that has been hitherto detailed must be present to our recollection4 #dh4 ,the impression of coloured objects remains in the eye like that of colourless ones1 but in this case the energy of the retina1 stimulated as it is to produce the opposite colour1 will be more apparent4 #di4 ,let a small piece of bright-coloured paper or silk stuff be held before a moderately lighted white surface2 let the observer look steadfastly on the small coloured object1 and let it be taken away after a time while his eyes remain unmoved2 the spectrum of another colour will then be visible on the white plane4 ,the coloured paper may be also left in its place while the eye is directed to another part of the white plane2 the same spectrum will be visible there too1 for it arises from an image which now belongs to the eye4 #ej4 ,in order at once to see what colour will be evoked by this contrast1 the chromatic circle#a may be referred to4 ,the colours are here arranged in a general way according to the natural order1 and the arrangement will be found to be directly applicable in the present case2 for the colours diametrically opposed to each other in this diagram are those which reciprocally evoke each other in the eye4 ,thus1 yellow demands purple2 orange1 blue2 red1 green2 and vice vers3 thus again all intermediate gradations reciprocally evoke each other2 the simpler colour demanding the compound1 and vice vers4--,note ,c4 #ea4 ,the cases here under consideration occur oftener than we are aware in ordinary life2 indeed1 an attentive observer sees these appearances everywhere1 while1 on the other hand1 the uninstructed1 like our predecessors1 consider them as temporary visual defects1 sometimes even as symptoms of disorders in the eye1 thus exciting serious apprehensions4 ,a few remarkable instances may here be inserted4 #eb4 ,i had entered an inn towards evening1 and1 as a well-favoured girl1 with a brilliantly fair complexion1 black hair1 and a scarlet bodice1 came into the room1 ,i looked attentively at her as she stood before me at some distance in half shadow4 ,as she presently afterwards turned away1 ,i saw on the white wall1 which was now before me1 a black face surrounded with a bright light1 while the dress of the perfectly distinct figure appeared of a beautiful sea-green4 #ec4 ,among the materials for optical experiments1 there are portraits with colours and shadows exactly opposite to the appearance of nature4 ,the spectator1 after having looked at one of these for a time1 will see the visionary figure tolerably true to nature4 ,this is conformable to the same principles1 and consistent with experience1 for1 in the former instance1 a negress with a white head-dress would have given me a white face surrounded with black4 ,in the case of the painted figures1 however1 which are commonly small1 the parts are not distinguishable by every one in the after-image4 #ed4 ,a phenomenon which has before excited attention among the observers of nature is to be attributed1 ,i am persuaded1 to the same cause4 ,it has been stated that certain flowers1 towards evening in summer1 coruscate1 become phosphorescent1 or emit a momentary light4 ,some persons have described their observation of this minutely4 ,i had often endeavoured to witness it myself1 and had even resorted to artificial contrivances to produce it4 ,on the #aith of ,june1 #agii1 late in the evening1 when the twilight was deepening into a clear night1 as ,i was walking up and down the garden with a friend1 we very distinctly observed a flame-like appearance near the oriental poppy1 the flowers of which are remarkable for their powerful red colour4 ,we approached the place and looked attentively at the flowers1 but could perceive nothing further1 till at last1 by passing and repassing repeatedly1 while we looked sideways on them1 we succeeded in renewing the appearance as often as we pleased4 ,it proved to be a physiological phenomenon1 such as others we have described1 and the apparent coruscation was nothing but the spectrum of the flower in the compensatory blue-green colour4 ,in looking directly at a flower the image is not produced1 but it appears immediately as the direction of the eye is altered4 ,again1 by looking sideways on the object1 a double image is seen for a moment1 for the spectrum then appears near and on the real object4 ,the twilight accounts for the eye being in a perfect state of repose1 and thus very susceptible1 and the colour of the poppy is sufficiently powerful in the summer twilight of the longest days to act with full effect and produce a compensatory image4 ,i have no doubt these appearances might be reduced to experiment1 and the same effect produced by pieces of coloured paper4 ,those who wish to take the most effectual means for observing the appearance in nature--suppose in a garden--should fix the eyes on the bright flowers selected for the purpose1 and1 immediately after1 look on the gravel path4 ,this will be seen studded with spots of the opposite colour4 ,the experiment is practicable on a cloudy day1 and even in the brightest sunshine1 for the sun-light1 by enhancing the brilliancy of the flower1 renders it fit to produce the compensatory colour sufficiently distinct to be perceptible even in a bright light4 ,thus1 peonies produce beautiful green1 marigolds vivid blue spectra4 #ee4 ,as the opposite colour is produced by a constant law in experiments with coloured objects on portions of the retina1 so the same effect takes place when the whole retina is impressed with a single colour4 ,we may convince ourselves of this by means of coloured glasses4 ,if we look long through a blue pane of glass1 everything will afterwards appear in sunshine to the naked eye1 even if the sky is grey and the scene colourless4 ,in like manner1 in taking off green spectacles1 we see all objects in a red light4 ,every decided colour does a certain violence to the eye1 and forces the organ to opposition4 #ef4 ,we have hitherto seen the opposite colours producing each other successively on the retina3 it now remains to show by experiment that the same effects can exist simultaneously4 ,if a coloured object impinges on one part of the retina1 the remaining portion at the same moment has a tendency to produce the compensatory colour4 ,to pursue a former experiment1 if we look on a yellow piece of paper placed on a white surface1 the remaining part of the organ has already a tendency to produce a purple hue on the colourless surface3 in this case the small portion of yellow is not powerful enough to produce this appearance distinctly1 but1 if a white paper is placed on a yellow wall1 we shall see the white tinged with a purple hue4 #eg4 ,although this experiment may be made with any colours1 yet red and green are particularly recommended for it1 because these colours seem powerfully to evoke each other4 ,numerous instances occur in daily experience4 ,if a green paper is seen through striped or flowered muslin1 the stripes or flowers will appear reddish4 ,a grey building seen through green pallisades appears in like manner reddish4 ,a modification of this tint in the agitated sea is also a compensatory colour3 the light side of the waves appears green in its own colour1 and the shadowed side is tinged with the opposite hue4 ,the different direction of the waves with reference to the eye produces the same effect4 ,objects seen through an opening in a red or green curtain appear to wear the opposite hue4 ,these appearances will present themselves to the attentive observer on all occasions1 even to an unpleasant degree4 #eh4 ,having made ourselves acquainted with the simultaneous exhibition of these effects in direct cases1 we shall find that we can also observe them by indirect means4 ,if we place a piece of paper of a bright orange colour on the white surface1 we shall1 after looking intently at it1 scarcely perceive the compensatory colour on the rest of the surface3 but when we take the orange paper away1 and when the blue spectrum appears in its place1 immediately as this spectrum becomes fully apparent1 the rest of the surface will be overspread1 as if by a flash1 with a reddish-yellow light1 thus exhibiting to the spectator in a lively manner the productive energy of the organ1 in constant conformity with the same law4 #ei4 ,as the compensatory colours easily appear1 where they do not exist in nature1 near and after the original opposite ones1 so they are rendered more intense where they happen to mix with a similar real hue4 ,in a court which was paved with grey limestone flags1 between which grass had grown1 the grass appeared of an extremely beautiful green when the evening clouds threw a scarcely perceptible reddish light on the pavement4 ,in an opposite case we find1 in walking through meadows1 where we see scarcely anything but green1 the stems of trees and the roads often gleam with a reddish hue4 ,this tone is not uncommon in the works of landscape painters1 especially those who practice in water-colours3 they probably see it in nature1 and thus1 unconsciously imitating it1 their colouring is criticised as unnatural4 #fj4 ,these phenomena are of the greatest importance1 since they direct our attention to the laws of vision1 and are a necessary preparation for future observations on colours4 ,they show that the eye especially demands completeness1 and seeks to eke out the colorific circle in itself4 ,the purple or violet colour suggested by yellow contains red and blue2 orange1 which responds to blue1 is composed of yellow and red2 green1 uniting blue and yellow1 demands red2 and so through all gradations of the most complicated combinations4 ,that we are compelled in this case to assume three leading colours has been already remarked by other observers4 #fa4 ,when in this completeness the elements of which it is composed are still appreciable by the eye1 the result is justly called harmony4 ,we shall subsequently endeavour to show how the theory of the harmony of colours may be deduced from these phenomena1 and how1 simply through these qualities1 colours may be capable of being applied to sthetic purposes4 ,this will be shown when we have gone through the whole circle of our observations1 returning to the point from which we started4 #a ,plate #a1 fig4 #c4 ,,vi4 ,,coloured ,,shadows4 #fb4 ,before1 however1 we proceed further1 we have yet to observe some very remarkable cases of the vivacity with which the suggested colours appear in the neighbourhood of others3 we allude to coloured shadows4 ,to arrive at these we first turn our attention to shadows that are colourless or negative4 #fc4 ,a shadow cast by the sun1 in its full brightness1 on a white surface1 gives us no impression of colour2 it appears black1 or1 if a contrary light 7here assumed to differ only in degree7 can act upon it1 it is only weaker1 half-lighted1 grey4 #fd4 ,two conditions are necessary for the existence of coloured shadows3 first1 that the principal light tinge the white surface with some hue2 secondly1 that a contrary light illumine to a certain extent the cast shadow4 #fe4 ,let a short1 lighted candle be placed at twilight on a sheet of white paper4 ,between it and the declining daylight let a pencil be placed upright1 so that its shadow thrown by the candle may be lighted1 but not overcome1 by the weak daylight3 the shadow will appear of the most beautiful blue4 #ff4 ,that this shadow is blue is immediately evident2 but we can only persuade ourselves by some attention that the white paper acts as a reddish yellow1 by means of which the complemental blue is excited in the eye4--,note ,d4 #fg4 ,in all coloured shadows1 therefore1 we must presuppose a colour excited or suggested by the hue of the surface on which the shadow is thrown4 ,this may be easily found to be the case by attentive consideration1 but we may convince ourselves at once by the following experiment4 #fh4 ,place two candles at night opposite each other on a white surface2 hold a thin rod between them upright1 so that two shadows be cast by it2 take a coloured glass and hold it before one of the lights1 so that the white paper appear coloured2 at the same moment the shadow cast by the coloured light and slightly illumined by the colourless one will exhibit the complemental hue4 #fi4 ,an important consideration suggests itself here1 to which we shall frequently have occasion to return4 ,colour itself is a degree of darkness 2 hence ,kircher is perfectly right in calling it lumen opacatum4 ,as it is allied to shadow1 so it combines readily with it2 it appears to us readily in and by means of shadow the moment a suggesting cause presents itself4 ,we could not refrain from adverting at once to a fact which we propose to trace and develop hereafter4--,note ,e4 #gj4 ,select the moment in twilight when the light of the sky is still powerful enough to cast a shadow which cannot be entirely effaced by the light of a candle4 ,the candle may be so placed that a double shadow shall be visible1 one from the candle towards the daylight1 and another from the daylight towards the candle4 ,if the former is blue the latter will appear orange-yellow3 this orange-yellow is in fact1 however1 only the yellow-red light of the candle diffused over the whole paper1 and which becomes visible in shadow4 #ga4 ,this is best exemplified by the former experiment with two candles and coloured glasses4 ,the surprising readiness with which shadow assumes a colour will again invite our attention in the further consideration of reflections and elsewhere4 #gb4 ,thus the phenomena of coloured shadows may be traced to their cause without difficulty4 ,henceforth let any one who sees an instance of the kind observe only with what hue the light surface on which they are thrown is tinged4 ,nay1 the colour of the shadow may be considered as a chromatoscope of the illumined surface1 for the spectator may always assume the colour of the light to be the opposite of that of the shadow1 and by an attentive examination may ascertain this to be the fact in every instance4 #gc4 ,these appearances have been a source of great perplexity to former observers3 for1 as they were remarked chiefly in the open air1 where they commonly appeared blue1 they were attributed to a certain inherent blue or blue colouring quality in the air4 ,the inquirer can1 however1 convince himself1 by the experiment with the candle in a room1 that no kind of blue light or reflection is necessary to produce the effect in question4 ,the experiment may be made on a cloudy day with white curtains drawn before the light1 and in a room where no trace of blue exists1 and the blue shadow will be only so much the more beautiful4 #gd4 ,de ,saussure1 in the description of his ascent of ,mont ,blanc1 says1 ,a second remark1 which may not be uninteresting1 relates to the colour of the shadows4 ,these1 notwithstanding the most attentive observation1 we never found dark blue1 although this had been frequently the case in the plain4 ,on the contrary1 in fifty-nine instances we saw them once yellowish1 six times pale bluish1 eighteen times colourless or black1 and thirty-four times pale violet4 ,some natural philosophers suppose that these colours arise from accidental vapours diffused in the air1 which communicate their own hues to the shadows2 not that the colours of the shadows are occasioned by the reflection of any given sky colour or interposition of any given air colour3 the above observations seem to favour this opinion4 ,the instances given by ,de ,saussure may be now explained and classed with analogous examples without difficulty4 ,at a great elevation the sky was generally free from vapours1 the sun shone in full force on the snow1 so that it appeared perfectly white to the eye3 in this case they saw the shadows quite colourless4 ,if the air was charged with a certain degree of vapour1 in consequence of which the light snow would assume a yellowish tone1 the shadows were violet-coloured1 and this effect1 it appears1 occurred oftenest4 ,they saw also bluish shadows1 but this happened less frequently2 and that the blue and violet were pale was owing to the surrounding brightness1 by which the strength of the shadows was mitigated4 ,once only they saw the shadow yellowish3 in this case1 as we have already seen 7#gj71 the shadow is cast by a colourless light1 and slightly illumined by a coloured one4 #ge4 ,in travelling over the ,harz in winter1 ,i happened to descend from the ,brocken towards evening2 the wide slopes extending above and below me1 the heath1 every insulated tree and projecting rock1 and all masses of both1 were covered with snow or hoar-frost4 ,the sun was sinking towards the ,oder ponds#a4 ,during the day1 owing to the yellowish hue of the snow1 shadows tending to violet had already been observable2 these might now be pronounced to be decidedly blue1 as the illumined parts exhibited a yellow deepening to orange4 ,but as the sun at last was about to set1 and its rays1 greatly mitigated by the thicker vapours1 began to diffuse a most beautiful red colour over the whole scene around me1 the shadow colour changed to a green1 in lightness to be compared to a sea-green1 in beauty to the green of the emerald4 ,the appearance became more and more vivid3 one might have imagined oneself in a fairy world1 for every object had clothed itself in the two vivid and so beautifully harmonising colours1 till at last1 as the sun went down1 the magnificent spectacle was lost in a grey twilight1 and by degrees in a clear moon-and-starlight night4 #gf4 ,one of the most beautiful instances of coloured shadows may be observed during the full moon4 ,the candle-light and moon-light may be contrived to be exactly equal in force2 both shadows may be exhibited with equal strength and clearness1 so that both colours balance each other perfectly4 ,a white surface being placed opposite the full moon1 and the candle being placed a little on one side at a due distance1 an opaque body is held before the white plane1 ,a double shadow will then be seen3 that cast by the moon and illumined by the candle-light will be a powerful red-yellow2 and contrariwise1 that cast by the candle and illumined by the moon will appear of the most beautiful blue4 ,the shadow1 composed of the union of the two shadows1 where they cross each other1 is black4 ,the yellow shadow 7#gd7 cannot perhaps be exhibited in a more striking manner4 ,the immediate vicinity of the blue and the interposing black shadow make the appearance the more agreeable4 ,it will even be found1 if the eye dwells long on these colours1 that they mutually evoke and enhance each other1 the increasing red in the one still producing its contrast1 viz4 a kind of sea-green4 #gg4 ,we are here led to remark that in this1 and in all cases1 a moment or two may perhaps be necessary to produce the complemental colour4 ,the retina must be first thoroughly impressed with the demanding hue before the responding one can be distinctly observable4 #gh4 ,when divers are under water1 and the sunlight shines into the diving-bell1 everything is seen in a red light 7the cause of which will be explained hereafter71 while the shadows appear green4 ,the very same phenomenon which ,i observed on a high mountain 7#ge7 is presented to others in the depths of the sea1 and thus ,nature throughout is in harmony with herself4 #gi4 ,some observations and experiments which equally illustrate what has been stated with regard to coloured objects and coloured shadows may be here added4 ,let a white paper blind be fastened inside the window on a winter evening2 in this blind let there be an opening1 through which the snow of some neighbouring roof can be seen4 ,towards dusk let a candle be brought into the room2 the snow seen through the opening will then appear perfectly blue1 because the paper is tinged with warm yellow by the candle-light4 ,the snow seen through the aperture is here equivalent to a shadow illumined by a contrary light 7#gf71 and may also represent a grey disk on a coloured surface 7#ef74 #hj4 ,another very interesting experiment may conclude these examples4 ,if we take a piece of green glass of some thickness1 and hold it so that the window bars be reflected in it1 they will appear double owing to the thickness of the glass4 ,the image which is reflected from the under surface of the glass will be green2 the image which is reflected from the upper surface1 and which should be colourless1 will appear red4 ,the experiment may be very satisfactorily made by pouring water into a vessel1 the inner surface of which can act as a mirror2 for both reflections may first be seen colourless while the water is pure1 and then by tinging it1 they will exhibit two opposite hues4 #a ,reservoirs in which water is collected from various small streams1 to work the mines4--,t4 ,,vii4 ,,faint ,,lights4 #ha4 ,light1 in its full force1 appears purely white1 and it gives this impression also in its highest degree of dazzling splendour4 ,light1 which is not so powerful1 can also1 under various conditions1 remain colourless4 ,several naturalists and mathematicians have endeavoured to measure its degrees--,lambert1 ,bouguer1 ,rumford4 #hb4 ,yet an appearance of colour presently manifests itself in fainter lights1 for in their relation to absolute light they resemble the coloured spectra of dazzling objects 7#ci74 #hc4 ,a light of any kind becomes weaker1 either when its own force1 from whatever cause1 is diminished1 or when the eye is so circumstanced or placed1 that it cannot be sufficiently impressed by the action of the light4 ,those appearances which may be called objective1 come under the head of physical colours4 ,we will only advert here to the transition from white to red heat in glowing iron4 ,we may also observe that the flames of lights at night appear redder in proportion to their distance from the eye4--,note ,f4 #hd4 ,candle-light at night acts as yellow when seen near2 we can perceive this by the effect it produces on other colours4 ,at night a pale yellow is hardly to be distinguished from white2 blue approaches to green1 and rose-colour to orange4 #he4 ,candle-light at twilight acts powerfully as a yellow light3 this is best proved by the purple blue shadows which1 under these circumstances1 are evoked by the eye4 #hf4 ,the retina may be so excited by a strong light that it cannot perceive fainter lights 7#aa73 if it perceive these they appear coloured3 hence candle-light by day appears reddish1 thus resembling1 in its relation to fuller light1 the spectrum of a dazzling object2 nay1 if at night we look long and intently on the flame of a light1 it appears to increase in redness4 #hg4 ,there are faint lights which1 notwithstanding their moderate lustre1 give an impression of a white1 or1 at the most1 of a light yellow appearance on the retina2 such as the moon in its full splendour4 ,rotten wood has even a kind of bluish light4 ,all this will hereafter be the subject of further remarks4 #hh4 ,if at night we place a light near a white or greyish wall so that the surface be illumined from this central point to some extent1 we find1 on observing the spreading light at some distance1 that the boundary of the illumined surface appears to be surrounded with a yellow circle1 which on the outside tends to red-yellow4 ,we thus observe that when light direct or reflected does not act in its full force1 it gives an impression of yellow1 of reddish1 and lastly even of red4 ,here we find the transition to halos which we are accustomed to see in some mode or other round luminous points4 ,,viii4 ,,subjective ,,halos4 #hi4 ,halos may be divided into subjective and objective4 ,the latter will be considered under the physical colours2 the first only belong here4 ,these are distinguished from the objective halos by the circumstance of their vanishing when the point of light which produces them on the retina is covered4 #ij4 ,we have before noticed the impression of a luminous object on the retina1 and seen that it appears larger3 but the effect is not at an end here1 it is not confined to the impression of the image2 an expansive action also takes place1 spreading from the centre4 #ia4 ,that a nimbus of this kind is produced round the luminous image in the eye may be best seen in a dark room1 if we look towards a moderately large opening in the window-shutter4 ,in this case the bright image is surrounded by a circular misty light4 ,i saw such a halo bounded by a yellow and yellow-red circle on opening my eyes at dawn1 on an occasion when ,i passed several nights in a bed-carriage4 #ib4 ,halos appear most vivid when the eye is susceptible from having been in a state of repose4 ,a dark background also heightens their appearance4 ,both causes account for our seeing them so strong if a light is presented to the eyes on waking at night4 ,these conditions were combined when ,descartes after sleeping1 as he sat in a ship1 remarked such a vividly-coloured halo round the light4 #ic4 ,a light must shine moderately1 not dazzle1 in order to produce the impression of a halo in the eye2 at all events the halos of dazzling lights cannot be observed4 ,we see a splendour of this kind round the image of the sun reflected from the surface of water4 #id4 ,a halo of this description1 attentively observed1 is found to be encircled towards its edge with a yellow border3 but even here the expansive action1 before alluded to1 is not at an end1 but appears still to extend in varied circles4 #ie4 ,several cases seem to indicate a circular action of the retina1 whether owing to the round form of the eye itself and its different parts1 or to some other cause4 #if4 ,if the eye is pressed only in a slight degree from the inner corner1 darker or lighter circles appear4 ,at night1 even without pressure1 we can sometimes perceive a succession of such circles emerging from1 or spreading over1 each other4 #ig4 ,we have already seen that a yellow border is apparent round the white space illumined by a light placed near it4 ,this may be a kind of objective halo4 7#hh47 #ih4 ,subjective halos may be considered as the result of a conflict between the light and a living surface4 ,from the conflict between the exciting principle and the excited1 an undulating motion arises1 which may be illustrated by a comparison with the circles on water4 ,the stone thrown in drives the water in all directions2 the effect attains a maximum1 it reacts1 and being opposed1 continues under the surface4 ,the effect goes on1 culminates again1 and thus the circles are repeated4 ,if we have ever remarked the concentric rings which appear in a glass of water on trying to produce a tone by rubbing the edge2 if we call to mind the intermitting pulsations in the reverberations of bells1 we shall approach a conception of what may take place on the retina when the image of a luminous object impinges on it1 not to mention that as a living and elastic structure1 it has already a circular principle in its organisation4--,note ,g4 #ii4 ,the bright circular space which appears round the shining object is yellow1 ending in red3 then follows a greenish circle1 which is terminated by a red border4 ,this appears to be the usual phenomenon where the luminous body is somewhat considerable in size4 ,these halos become greater the more distant we are from the luminous object4 #ajj4 ,halos may1 however1 appear extremely small and numerous when the impinging image is minute1 yet powerful1 in its effect4 ,the experiment is best made with a piece of gold-leaf placed on the ground and illumined by the sun4 ,in these cases the halos appear in variegated rays4 ,the iridescent appearance produced in the eye when the sun pierces through the leaves of trees seems also to belong to the same class of phenomena4 ,,pathological ,,colours4 ,,appendix4 #aja4 ,we are now sufficiently acquainted with the physiological colours to distinguish them from the pathological4 ,we know what appearances belong to the eye in a healthy state1 and are necessary to enable the organ to exert its complete vitality and activity4 #ajb4 ,morbid phenomena indicate in like manner the existence of organic and physical laws3 for if a living being deviates from those rules with reference to which it is constructed1 it still seeks to agree with the general vitality of nature in conformity with general laws1 and throughout its whole course still proves the constancy of those principles on which the universe has existed1 and by which it is held together4 #ajc4 ,we will here first advert to a very remarkable state in which the vision of many persons is found to be4 ,as it presents a deviation from the ordinary mode of seeing colours1 it might be fairly classed under morbid impressions2 but as it is consistent in itself1 as it often occurs1 may extend to several members of a family1 and probably does not admit of cure1 we may consider it as bordering only on the nosological cases1 and therefore place it first4 #ajd4 ,i was acquainted with two individuals not more than twenty years of age1 who were thus affected3 both had bluish-grey eyes1 an acute sight for near and distant objects1 by day-light and candle-light1 and their mode of seeing colours was in the main quite similar4 #aje4 ,they agreed with the rest of the world in denominating white1 black1 and grey in the usual manner4 ,both saw white untinged with any hue4 ,one saw a somewhat brownish appearance in black1 and in grey a somewhat reddish tinge4 ,in general they appeared to have a very delicate perception of the gradations of light and dark4 #ajf4 ,they appeared to see yellow1 red-yellow1 and yellow-red1#a like others3 in the last case they said they saw the yellow passing as it were over the red as if glazed3 some thickly-ground carmine1 which had dried in a saucer1 they called red4 #ajg4 ,but now a striking difference presented itself4 ,if the carmine was passed thinly over the white saucer1 they would compare the light colour thus produced to the colour of the sky1 and call it blue4 ,if a rose was shown them beside it1 they would1 in like manner1 call it blue2 and in all the trials which were made1 it appeared that they could not distinguish light blue from rose-colour4 ,they confounded rose-colour1 blue1 and violet on all occasions3 these colours only appeared to them to be distinguished from each other by delicate shades of lighter1 darker1 intenser1 or fainter appearance4 #ajh4 ,again they could not distinguish green from dark orange1 nor1 more especially1 from a red brown4 #aji4 ,if any one1 accidentally conversing with these individuals1 happened to question them about surrounding objects1 their answers occasioned the greatest perplexity1 and the interrogator began to fancy his own wits were out of order4 ,with some method we may1 however1 approach to a nearer knowledge of the law of this deviation from the general law4 #aaj4 ,these persons1 as may be gathered from what has been stated1 saw fewer colours than other people3 hence arose the confusion of different colours4 ,they called the sky rose-colour1 and the rose blue1 or vice vers4 ,the question now is3 did they see both blue or both rose-colour8 did they see green orange1 or orange green8 #aaa4 ,this singular enigma appears to solve itself1 if we assume that they saw no blue1 but1 instead of it1 a light pure red1 a rose-colour4 ,we can comprehend what would be the result of this by means of the chromatic diagram4 #aab4 ,if we take away blue from the chromatic circle we shall miss violet and green as well4 ,pure red occupies the place of blue and violet1 and in again mixing with yellow the red produces orange where green should be4 #aac4 ,professing to be satisfied with this mode of explanation1 we have named this remarkable deviation from ordinary vision ,acyanoblepsia4#b ,we have prepared some coloured figures for its further elucidation1 and in explaining these we shall add some further details4 ,among the examples will be found a landscape1 coloured in the mode in which the individuals alluded to appeared to see nature3 the sky rose-colour1 and all that should be green varying from yellow to brown red1 nearly as foliage appears to us in autumn#c4--,note ,h4 #aad4 ,we now proceed to speak of morbid and other extraordinary affections of the retina1 by which the eye may be susceptible of an appearance of light without external light1 reserving for a future occasion the consideration of galvanic light4 #aae4 ,if the eye receives a blow1 sparks seem to spread from it4 ,in some states of body1 again1 when the blood is heated1 and the system much excited1 if the eye is pressed first gently1 and then more and more strongly1 a dazzling and intolerable light may be excited4 #aaf4 ,if those who have been recently couched experience pain and heat in the eye1 they frequently see fiery flashes and sparks3 these symptoms last sometimes for a week or fortnight1 or till the pain and heat diminish4 #aag4 ,a person suffering from ear-ache saw sparks and balls of light in the eye during each attack1 as long as the pain lasted4 #aah4 ,persons suffering from worms often experience extraordinary appearances in the eye1 sometimes sparks of fire1 sometimes spectres of light1 sometimes frightful figures1 which they cannot by an effort of the will cease to see3 sometimes these appearances are double4 #aai4 ,hypochondriacs frequently see dark objects1 such as threads1 hairs1 spiders1 flies1 wasps4 ,these appearances also exhibit themselves in the incipient hard cataract4 ,many see semi-transparent small tubes1 forms like wings of insects1 bubbles of water of various sizes1 which fall slowly down1 if the eye is raised3 sometimes these congregate together so as to resemble the spawn of frogs2 sometimes they appear as complete spheres1 sometimes in the form of lenses4 #abj4 ,as light appeared1 in the former instances1 without external light1 so also these images appear without corresponding external objects4 ,the images are sometimes transient1 sometimes they last during the patient's life4 ,colour1 again1 frequently accompanies these impressions3 for hypochondriacs often see yellow-red stripes in the eye3 these are generally more vivid and numerous in the morning1 or when lasting4 #aba4 ,we have before seen that the impression of any object may remain for a time in the eye3 this we have found to be a physiological phenomenon 7#bc73 the excessive duration of such an impression1 on the other band1 may be considered as morbid4 #abb4 ,the weaker the organ the longer the impression of the image lasts4 ,the retina does not so soon recover itself2 and the effect may be considered as a kind of paralysis 7#bh74 #abc4 ,this is not to be wondered at in the case of dazzling lights4 ,if any one looks at the sun1 he may retain the image in his eyes for several days4 ,boyle relates an instance of ten years4 #abd4 ,the same takes place1 in a certain degree1 with regard to objects that are not dazzling4 ,bsch relates of himself that the image of an engraving1 complete in all its parts1 was impressed on his eye for seventeen minutes4 #abe4 ,a person inclined to fulness of blood retained the image of a bright red calico1 with white spots1 many minutes in the eye1 and saw it float before everything like a veil4 ,it only disappeared by rubbing the eye for some time4 #abf4 ,scherfer observes that the red colour1 which is the consequence of a powerful impression of light1 may last for some hours4 #abg4 ,as we can produce an appearance of light on the retina by pressure on the eyeball1 so by a gentle pressure a red colour appears1 thus corresponding with the after-image of an impression of light4 #abh4 ,many sick persons1 on awaking1 see everything in the colour of the morning sky1 as if through a red veil3 so1 if in the evening they doze and wake again1 the same appearance presents itself4 ,it remains for some minutes1 and always disappears if the eye is rubbed a little4 ,red stars and balls sometimes accompany the impression4 ,this state may last for a considerable time4 #abi4 ,the aronauts1 particularly ,zambeccari and his companions1 relate that they saw the moon blood-red at the highest elevation4 ,as they had ascended above the vapours of the earth1 through which we see the moon and sun naturally of such a colour1 it may be suspected that this appearance may be classed with the pathological colours4 ,the senses1 namely1 may be so influenced by an unusual state1 that the whole nervous system1 and particularly the retina1 may sink into a kind of inertness and inexcitability4 ,hence it is not impossible that the moon might act as a very subdued light1 and thus produce the impression of the red colour4 ,the sun even appeared blood-red to the aronauts of ,hamburgh4 ,if those who are at some elevation in a balloon scarcely hear each other speak1 may not this1 too1 be attributed to the inexcitable state of the nerves as well as to the thinness of the air8 #acj4 ,objects are often seen by sick persons in variegated colours4 ,boyle relates an instance of a lady1 who1 after a fall by which an eye was bruised1 saw all objects1 but especially white objects1 glittering in colours1 even to an intolerable degree4 #aca4 ,physicians give the name of ,chrupsia to an affection of the sight1 occurring in typhoid maladies4 ,in these cases the patients state that they see the boundaries of objects coloured where light and dark meet4 ,a change probably takes place in the humours of the eye1 through which their achromatism is affected4 #acb4 ,in cases of milky cataract1 a very turbid crystalline lens causes the patient to see a red light4 ,in a case of this kind1 which was treated by the application of electricity1 the red light changed by degrees to yellow1 and at last to white1 when the patient again began to distinguish objects4 ,these changes of themselves warranted the conclusion that the turbid state of the lens was gradually approaching the transparent state4 ,we shall be enabled easily to trace this effect to its source as soon as we become better acquainted with the physical colours4 #acc4 ,if again it may be assumed that a jaundiced patient sees through an actually yellow-coloured humour1 we are at once referred to the department of chemical colours1 and it is thus evident that we can only thoroughly investigate the chapter of pathological colours when we have made ourselves acquainted with the whole range of the remaining phenomena4 ,what has been adduced may therefore suffice for the present1 till we resume the further consideration of this portion of our subject4 #acd4 ,in conclusion we may1 however1 at once advert to some peculiar states or dispositions of the organ4 ,there are painters who1 instead of rendering the colours of nature1 diffuse a general tone1 a warm or cold hue1 over the picture4 ,in some1 again1 a predilection for certain colours displays itself2 in others a want of feeling for harmony4 #ace4 ,lastly1 it is also worthy of remark1 that savage nations1 uneducated people1 and children have a great predilection for vivid colours2 that animals are excited to rage by certain colours2 that people of refinement avoid vivid colours in their dress and the objects that are about them1 and seem inclined to banish them altogether from their presence4--,note ,i4 #a ,it has been found necessary to follow the author's nomenclature throughout--,t4 #b ,non-perception of blue4 #c ,it has not been thought necessary to copy the plates here referred to4--,t4 ,,part ,,ii4 ,,physical ,,colours4 #acf4 ,we give this designation to colours which are produced by certain material mediums3 these mediums1 however1 have no colour themselves1 and may be either transparent1 semi-transparent yet transmitting light1 or altogether opaque4 ,the colours in question are thus produced in the eye through such external given causes1 or are merely reflected to the eye when by whatever means they are already produced without us4 ,although we thus ascribe to them a certain objective character1 their distinctive quality still consists in their being transient1 and not to be arrested4 #acg4 ,they are called by former investigators colores apparentes1 fluxi1 fugitivi1 phantastici1 falsi1 variantes4 ,they are also called speciosi and emphatici1 on account of their striking splendour4 ,they are immediately connected with the physiological colours1 and appear to have but little more reality3 for1 while in the production of the physiological colours the eye itself was chiefly efficient1 and we could only perceive the phenomena thus evoked within ourselves1 but not without us1 we have now to consider the fact that colours are produced in the eye by means of colourless objects2 that we thus too have a colourless surface before us which is acted upon as the retina itself is1 and that we can perceive the appearance produced upon it without us4 ,in such a process1 however1 every observation will convince us that we have to do with colours in a progressive and mutable1 but not in a final or complete1 state4 #ach4 ,hence1 in directing our attention to these physical colours1 we find it quite possible to place an objective phenomenon beside a subjective one1 and often by means of the union of the two successfully to penetrate farther into the nature of the appearance4 #aci4 ,thus1 in the observations by which we become acquainted with the physical colours1 the eye is not to be considered as acting alone2 nor is the light ever to be considered in immediate relation with the eye3 but we direct our attention especially to the various effects produced by mediums1 those mediums being themselves colourless4 #adj4 ,light under these circumstances may be affected by three conditions4 ,first1 when it flashes back from the surface of a medium2 in considering which catoptrical experiments invite our attention4 ,secondly1 when it passes by the edge of a medium3 the phenomena thus produced were formerly called perioptical2 we prefer the term paroptical4 ,thirdly1 when it passes through either a merely light-transmitting or an actually transparent body2 thus constituting a class of appearances on which dioptrical experiments are founded4 ,we have called a fourth class of physical colours epoptical1 as the phenomena exhibit themselves on the colourless surface of bodies under various conditions1 without previous or actual dye 774--,note ,k4 #ada4 ,in examining these categories with reference to our three leading divisions1 according to which we consider the phenomena of colours in a physiological1 physical1 or chemical view1 we find that the catoptrical colours are closely connected with the physiological2 the paroptical are already somewhat more distinct and independent2 the dioptrical exhibit themselves as entirely and strictly physical1 and as having a decidedly objective character2 the epoptical1 although still only apparent1 may be considered as the transition to the chemical colours4 #adb4 ,if we were desirous of prosecuting our investigation strictly in the order of nature1 we ought to proceed according to the classification which has just been made2 but in didactic treatises it is not of so much consequence to connect as to duly distinguish the various divisions of a subject1 in order that at last1 when every single class and case has been presented to the mind1 the whole may be embraced in one comprehensive view4 ,we therefore turn our attention forthwith to the dioptrical class1 in order at once to give the reader the full impression of the physical colours1 and to exhibit their characteristics the more strikingly4 ,,ix4 ,,dioptrical ,,colours4 #adc4 ,colours are called dioptrical when a colourless medium is necessary to produce them2 the medium must be such that light and darkness can act through it either on the eye or on opposite surfaces4 ,it is thus required that the medium should be transparent1 or at least capable1 to a certain degree1 of transmitting light4 #add4 ,according to these conditions we divide the dioptrical phenomena into two classes1 placing in the first those which are produced by means of imperfectly transparent1 yet light-transmitting mediums2 and in the second such as are exhibited when the medium is in the highest degree transparent4 ,x4 ,,dioptrical ,,colours ,,of ,,the ,,first ,,class4 #ade4 ,space1 if we assume it to be empty1 would have the quality of absolute transparency to our vision4 ,if this space is filled so that the eye cannot perceive that it is so1 there exists a more or less material transparent medium1 which may be of the nature of air and gas1 may be fluid or even solid4 #adf4 ,the pure and light-transmitting semi-transparent medium is only an accumulated form of the transparent medium4 ,it may therefore be presented to us in three modes4 #adg4 ,the extreme degree of this accumulation is white2 the simplest1 brightest1 first1 opaque occupation of space4 #adh4 ,transparency itself1 empirically considered1 is already the first degree of the opposite state4 ,the intermediate degrees from this point to opaque white are infinite4 #adi4 ,at whatever point short of opacity we arrest the thickening medium1 it exhibits simple and remarkable phenomena when placed in relation with light and darkness4 #aej4 ,the highest degree of light1 such as that of the sun1 of phosphorus burning in oxygen1 is dazzling and colourless3 so the light of the fixed stars is for the most part colourless4 ,this light1 however1 seen through a medium but very slightly thickened1 appears to us yellow4 ,if the density of such a medium be increased1 or if its volume become greater1 we shall see the light gradually assume a yellow-red hue1 which at last deepens to a ruby-colour4--,note ,l4 #aea4 ,if on the other hand darkness is seen through a semi-transparent medium1 which is itself illumined by a light striking on it1 a blue colour appears3 this becomes lighter and paler as the density of the medium is increased1 but on the contrary appears darker and deeper the more transparent the medium becomes3 in the least degree of dimness short of absolute transparence1 always supposing a perfectly colourless medium1 this deep blue approaches the most beautiful violet4 #aeb4 ,if this effect takes place in the eye as here described1 and may thus be pronounced to be subjective1 it remains further to convince ourselves of this by objective phenomena4 ,for a light thus mitigated and subdued illumines all objects in like manner with a yellow1 yellow-red1 or red hue2 and1 although the effect of darkness through the non-transparent medium does not exhibit itself so powerfully1 yet the blue sky displays itself in the camera obscura very distinctly on white paper1 as well as every other material colour4 #aec4 ,in examining the cases in which this important leading phenomenon appears1 we naturally mention the atmospheric colours first3 most of these may be here introduced in order4 #aed4 ,the sun seen through a certain degree of vapour appears with a yellow disk2 the centre is often dazzlingly yellow when the edges are already red4 ,the orb seen through a thick yellow mist appears ruby-red 7as was the case in #agid1 even in the north72 the same appearance is still more decided1 owing to the state of the atmosphere1 when the scirocco prevails in southern climates3 the clouds generally surrounding the sun in the latter case are of the same colour1 which is reflected again on all objects4 ,the red hues of morning and evening are owing to the same cause4 ,the sun is announced by a red light1 in shining through a greater mass of vapours4 ,the higher he rises1 the yellower and brighter the light becomes4 #aee4 ,if the darkness of infinite space is seen through atmospheric vapours illumined by the day-light1 the blue colour appears4 ,on high mountains the sky appears by day intensely blue1 owing to the few thin vapours that float before the endless dark space3 as soon as we descend in the valleys1 the blue becomes lighter2 till at last1 in certain regions1 and in consequence of increasing vapours1 it altogether changes to a very pale blue4 #aef4 ,the mountains1 in like manner1 appear to us blue2 for1 as we see them at so great a distance that we no longer distinguish the local tints1 and as no light reflected from their surface acts on our vision1 they are equivalent to mere dark objects1 which1 owing to the interposed vapours1 appear blue4 #aeg4 ,so we find the shadowed parts of nearer objects are blue when the air is charged with thin vapours4 #aeh4 ,the snow-mountains1 on the other hand1 at a great distance1 still appear white1 or approaching to a yellowish hue1 because they act on our eyes as brightness seen through atmospheric vapour4 #aei4 ,the blue appearance at the lower part of the flame of a candle belongs to the same class of phenomena4 ,if the flame be held before a white ground1 no blue will be seen1 but this colour will immediately appear if the flame is opposed to a black ground4 ,this phenomenon may be exhibited most strikingly with a spoonful of lighted spirits of wine4 ,we may thus consider the lower part of the flame as equivalent to the vapour which1 although infinitely thin1 is still apparent before the dark surface2 it is so thin1 that one may easily see to read through it3 on the other hand1 the point of the flame which conceals objects from our sight is to be considered as a self-illuminating body4 #afj4 ,lastly1 smoke is also to be considered as a semi-transparent medium1 which appears to us yellow or reddish before a light ground1 but blue before a dark one4 #afa4 ,if we now turn our attention to fluid mediums1 we find that water1 deprived in a very slight degree of its transparency1 produces the same effects4 #afb4 ,the infusion of the lignum nephriticum 7guilandina ,linni71 which formerly excited so much attention1 is only a semi-transparent liquor1 which in dark wooden cups must appear blue1 but held towards the sun in a transparent glass must exhibit a yellow appearance4 #afc4 ,a drop of scented water1 of spirit varnish1 of several metallic solutions1 may be employed to give various degrees of opacity to water for such experiments4 ,spirit of soap perhaps answers best4 #afd4 ,the bottom of the sea appears to divers of a red colour in bright sunshine3 in this case the water1 owing to its depth1 acts as a semi-transparent medium4 ,under these circumstances1 they find the shadows green1 which is the complemental colour4 #afe4 ,among solid mediums the opal attracts our attention first3 its colours are1 at least1 partly to be explained by the circumstance that it is1 in fact1 a semi-transparent medium1 through which sometimes light1 sometimes dark1 substrata are visible4 #aff4 ,for these experiments1 however1 the opal-glass 7vitrum astroides1 girasole7 is the most desirable material4 ,it is prepared in various ways1 and its semi-opacity is produced by metallic oxydes4 ,the same effect is produced also by melting pulverised and calcined bones together with the glass1 on which account it is also known by the name of beinglas2 but1 prepared in this mode1 it easily becomes too opaque4 #afg4 ,this glass may be adapted for experiments in various ways3 it may either be made in a very slight degree non-transparent1 in which case the light seen through various layers placed one upon the other may be deepened from the lightest yellow to the deepest red1 or1 if made originally more opaque1 it may be employed in thinner or thicker lamin4 ,the experiments may be successfully made in both ways3 in order1 however1 to see the bright blue colour1 the glass should neither be too opaque nor too thick4 ,for1 as it is quite natural that darkness must act weakly through the semi-transparent medium1 so this medium1 if too thick1 soon approaches whiteness4 #afh4 ,panes of glass throw a yellow light on objects through those parts where they happen to be semi-opaque1 and these same parts appear blue if we look at a dark object through them4 #afi4 ,smoked glass may be also mentioned here1 and is1 in like manner1 to be considered as a semi-opaque medium4 ,it exhibits the sun more or less ruby-coloured2 and1 although this appearance may be attributed to the black-brown colour of the soot1 we may still convince ourselves that a semi-transparent medium here acts if we hold such a glass moderately smoked1 and lit by the sun on the unsmoked side1 before a dark object1 for we shall then perceive a bluish appearance4 #agj4 ,a striking experiment may be made in a dark room with sheets of parchment4 ,if we fasten a piece of parchment before the opening in the window-shutter when the sun shines1 it will appear nearly white2 by adding a second1 a yellowish colour appears1 which still increases as more leaves are added1 till at last it changes to red4 #aga4 ,a similar effect1 owing to the state of the crystalline lens in milky cataract1 has been already adverted to 7#aca74 #agb4 ,having now1 in tracing these phenomena1 arrived at the effect of a degree of opacity scarcely capable of transmitting light1 we may here mention a singular appearance which was owing to a momentary state of this kind4 ,a portrait of a celebrated theologian had been painted some years before the circumstance to which we allude1 by an artist who was known to have considerable skill in the management of his materials4 ,the very reverend individual was represented in a rich velvet dress1 which was not a little admired1 and which attracted the eye of the spectator almost more than the face4 ,the picture1 however1 from the effect of the smoke of lamps and dust1 had lost much of its original vivacity4 ,it was1 therefore1 placed in the hands of a painter1 who was to clean it1 and give it a fresh coat of varnish4 ,this person began his operations by carefully washing the picture with a sponge3 no sooner1 however1 had he gone over the surface once or twice1 and wiped away the first dirt1 than to his amazement the black velvet dress changed suddenly to a light blue plush1 which gave the ecclesiastic a very secular1 though somewhat old-fashioned1 appearance4 ,the painter did not venture to go on with his washing3 he could not comprehend how a light blue should be the ground of the deepest black1 still less how he could so suddenly have removed a glazing colour capable of converting the one tint to the other4 ,at all events1 he was not a little disconcerted at having spoilt the picture to such an extent4 ,nothing to characterize the ecclesiastic remained but the richly-curled round wig1 which made the exchange of a faded plush for a handsome new velvet dress far from desirable4 ,meanwhile1 the mischief appeared irreparable1 and the good artist1 having turned the picture to the wall1 retired to rest with a mind ill at ease4 ,but what was his joy the next morning1 when1 on examining the picture1 he beheld the black velvet dress again in its full splendour4 ,he could not refrain from again wetting a corner1 upon which the blue colour again appeared1 and after a time vanished4 ,on hearing of this phenomenon1 ,i went at once to see the miraculous picture4 ,a wet sponge was passed over it in my presence1 and the change quickly took place4 ,i saw a somewhat faded1 but decidedly light blue plush dress1 the folds under the arm being indicated by some brown strokes4 ,i explained this appearance to myself by the doctrine of the semi-opaque medium4 ,the painter1 in order to give additional depth to his black1 may have passed some particular varnish over it3 on being washed1 this varnish imbibed some moisture1 and hence became semi-opaque1 in consequence of which the black underneath immediately appeared blue4 ,perhaps those who are practically acquainted with the effect of varnishes may1 through accident or contrivance1 arrive at some means of exhibiting this singular appearance1 as an experiment1 to those who are fond of investigating natural phenomena4 ,notwithstanding many attempts1 ,i could not myself succeed in re-producing it4 #agc4 ,having now traced the most splendid instances of atmospheric appearances1 as well as other less striking yet sufficiently remarkable cases1 to the leading examples of semi-transparent mediums1 we have no doubt that attentive observers of nature will carry such researches further1 and accustom themselves to trace and explain the various appearances which present themselves in every-day experience on the same principle3 we may also hope that such investigators will provide themselves with an adequate apparatus in order to place remarkable facts before the eyes of others who may be desirous of information4 #agd4 ,we venture1 once for all1 to call the leading appearance in question1 as generally described in the foregoing pages1 a primordial and elementary phenomenon2 and we may here be permitted at once to state what we understand by the term4 #age4 ,the circumstances which come under our notice in ordinary observation are1 for the most part1 insulated cases1 which1 with some attention1 admit of being classed under general leading facts4 ,these again range themselves under theoretical rubrics which are more comprehensive1 and through which we become better acquainted with certain indispensable conditions of appearances in detail4 ,from henceforth everything is gradually arranged under higher rules and laws1 which1 however1 are not to be made intelligible by words and hypotheses to the understanding merely1 but1 at the same time1 by real phenomena to the senses4 ,we call these primordial phenomena1 because nothing appreciable by the senses lies beyond them1 on the contrary1 they are perfectly fit to be considered as a fixed point to which we first ascended1 step by step1 and from which we may1 in like manner1 descend to the commonest case of every-day experience4 ,such an original phenomenon is that which has lately engaged our attention4 ,we see on the one side light1 brightness2 on the other darkness1 obscurity3 we bring the semi-transparent medium between the two1 and from these contrasts and this medium the colours develop themselves1 contrasted1 in like manner1 but soon1 through a reciprocal relation1 directly tending again to a point of union4#a #agf4 ,with this conviction we look upon the mistake that has been committed in the investigation of this subject to be a very serious one1 inasmuch as a secondary phenomenon has been thus placed higher in order--the primordial phenomenon has been degraded to an inferior place2 nay1 the secondary phenomenon has been placed at the head1 a compound effect has been treated as simple1 a simple appearance as compound3 owing to this contradiction1 the most capricious complication and perplexity have been introduced into physical inquiries1 the effects of which are still apparent4 #agg4 ,but when even such a primordial phenomenon is arrived at1 the evil still is that we refuse to recognise it as such1 that we still aim at something beyond1 although it would become us to confess that we are arrived at the limits of experimental knowledge4 ,let the observer of nature suffer the primordial phenomenon to remain undisturbed in its beauty2 let the philosopher admit it into his department1 and he will find that important elementary facts are a worthier basis for further operations than insulated cases1 opinions1 and hypotheses4--,note ,m4 #a ,that is 7according to the author's statement #aej4 #aea47 both tend to red2 the yellow deepening to orange as the comparatively dark medium is thickened before brightness2 the blue deepening to violet as the light medium is thinned before darkness4--,t4 ,pg #gd ,,xi4 ,,dioptrical ,,colours ,,of ,,the ,,second ,,class4--,,refraction4 #agh4 ,dioptrical colours of both classes are closely connected1 as will presently appear on a little examination4 ,those of the first class appeared through semi-transparent mediums1 those of the second class will now appear through transparent mediums4 ,but since every substance1 however transparent1 may be already considered to partake of the opposite quality 7as every accumulation of a medium called transparent proves71 so the near affinity of the two classes is sufficiently manifest4 #agi4 ,we will1 however1 first consider transparent mediums abstractedly as such1 as entirely free from any degree of opacity1 and direct our whole attention to a phenomenon which here presents itself1 and which is known by the name of refraction4 #ahj4 ,in treating of the physiological colours1 we have already had occasion to vindicate what ,pg #ge were formerly called illusions of sight1 as the active energies of the healthy and duly efficient eye 7#b71 and we are now again invited to consider similar instances confirming the constancy of the laws of vision4 #aha4 ,throughout nature1 as presented to the senses1 everything depends on the relation which things bear to each other1 but especially on the relation which man1 the most important of these1 bears to the rest4 ,hence the world divides itself into two parts1 and the human being as subject1 stands opposed to the object4 ,thus the practical man exhausts himself in the accumulation of facts1 the thinker in speculation2 each being called upon to sustain a conflict which admits of no peace and no decision4 #ahb4 ,but still the main point always is1 whether the relations are truly seen4 ,as our senses1 if healthy1 are the surest witnesses of external relations1 so we may be convinced that1 in all instances where they appear to contradict reality1 they lay the greater and surer stress on true relations4 ,thus a distant object appears to us smaller2 and precisely by this means we are aware of distance4 ,we produced coloured appearances on colourless objects1 through colourless mediums1 and at the same moment our attention was called to the degree of opacity in the medium4 #ahc4 ,thus the different degrees of opacity in so-called transparent mediums1 nay1 even other physical and chemical properties belonging to them1 are known to our vision by means of refraction1 and invite us to make further trials in order to penetrate more completely by physical and chemical means into those secrets which are already opened to our view on one side4 #ahd4 ,objects seen through mediums more or less transparent do not appear to us in the place which they should occupy according to the laws of perspective4 ,on this fact the dioptrical colours of the second class depend4 #ahe4 ,those laws of vision which admit of being expressed in mathematical formul are based on the principle that1 as light proceeds in straight lines1 it must be possible to draw a straight line from the eye to any given object in order that it be seen4 ,if1 therefore1 a case arises in which the light arrives to us in a bent or broken line1 that we see the object by means of a bent or broken line1 we are at once informed that the medium between the eye and the object is denser1 or that it has assumed this or that foreign nature4 #ahf4 ,this deviation from the law of right-lined vision is known by the general term of refraction2 and1 although we may take it for granted that our readers are sufficiently acquainted with its effects1 yet we will here once more briefly exhibit it in its objective and subjective point of view4 #ahg4 ,let the sun shine diagonally into an empty cubical vessel1 so that the opposite side be illumined1 but not the bottom3 let water be then poured into this vessel1 and the direction of the light will be immediately altered2 for a part of the bottom is shone upon4 ,at the point where the light enters the thicker medium it deviates from its rectilinear direction1 and appears broken3 hence the phenomenon is called the breaking 7brechung7 or refraction4 ,thus much of the objective experiment4 #ahh4 ,we arrive at the subjective fact in the following mode3--,let the eye be substituted for the sun3 let the sight be directed in like manner ,pg #gh diagonally over one side1 so that the opposite inner side be entirely seen1 while no part of the bottom is visible4 ,on pouring in water the eye will perceive a part of the bottom2 and this takes place without our being aware that we do not see in a straight line2 for the bottom appears to us raised1 and hence we give the term elevation 7hebung7 to the subjective phenomenon4 ,some points1 which are particularly remarkable with reference to this1 will be adverted to hereafter4 #ahi4 ,were we now to express this phenomenon generally1 we might here repeat1 in conformity with the view lately taken1 that the relation of the objects is changed or deranged4 #aij4 ,but as it is our intention at present to separate the objective from the subjective appearances1 we first express the phenomenon in a subjective form1 and say1--a derangement or displacement of the object seen1 or to be seen1 takes place4 #aia4 ,but that which is seen without a limiting outline may be thus affected without our perceiving the change4 ,on the other hand1 if what we look at has a visible termination1 we have an evident indication that a displacement occurs4 ,if1 therefore1 ,pg #gi we wish to ascertain the relation or degree of such a displacement1 we must chiefly confine ourselves to the alteration of surfaces with visible boundaries2 in other words1 to the displacement of circumscribed objects4 #aib4 ,the general effect may take place through parallel mediums1 for every parallel medium displaces the object by bringing it perpendicularly towards the eye4 ,the apparent change of position is1 however1 more observable through mediums that are not parallel4 #aic4 ,these latter may be perfectly spherical1 or may be employed in the form of convex or concave lenses4 ,we shall make use of all these as occasion may require in our experiments4 ,but as they not only displace the object from its position1 but alter it in various ways1 we shall1 in most cases1 prefer employing mediums with surfaces1 not1 indeed1 parallel with reference to each other1 but still altogether plane1 namely1 prisms4 ,these have a triangle for their base1 and may1 it is true1 be considered as portions of a lens1 but they are particularly available for our experiments1 inasmuch as they very perceptibly displace the object from its position1 without producing a remarkable distortion4 #aid4 ,and now1 in order to conduct our observations with as much exactness as possible1 and to avoid all confusion and ambiguity1 we confine ourselves at first to ,,subjective ,,experiments1 in which1 namely1 the object is seen by the observer through a refracting medium4 ,as soon as we have treated these in due series1 the objective experiments will follow in similar order4 ,,xii4 ,,refraction ,,without ,,the ,,appearance ,,of ,,colour4 #aie4 ,refraction can visibly take place without our perceiving an appearance of colour4 ,to whatever extent a colourless or uniformly coloured surface may be altered as to its position by refraction1 no colour consequent upon refraction appears within it1 provided it has no outline or boundary4 ,we may convince ourselves of this in various ways4 #aif4 ,place a glass cube on any larger surface1 and look through the glass perpendicularly or obliquely1 the unbroken surface opposite the eye appears altogether raised1 but no colour exhibits itself4 ,if we look at a pure grey or blue sky or a uniformly white or coloured wall through a prism1 the portion of the surface which the eye thus embraces will be altogether changed as to its position1 without our therefore observing the smallest appearance of colour4 ,,xiii4 ,,conditions ,,of ,,the ,,appearance ,,of ,,colour4 #aig4 ,although in the foregoing experiments we have found all unbroken surfaces1 large or small1 colourless1 yet at the outlines or boundaries1 where the surface is relieved upon a darker or lighter object1 we observe a coloured appearance4 #aih4 ,outline1 as well as surface1 is necessary to constitute a figure or circumscribed object4 ,we therefore express the leading fact thus3 circumscribed objects must be displaced by refraction in order to the exhibition of an appearance of colour4 #aii4 ,we place before us the simplest object1 a light disk on a dark ground 7,a74#a ,a displacement occurs with regard to this object1 if we apparently extend its outline from the centre by magnifying it4 ,this may be done with any convex glass1 and in this case we see a blue edge 7,b74 #bjj4 ,we can1 to appearance1 contract the circumference of the same light disk towards the centre by diminishing the object2 the edge will then appear yellow 7,c74 ,this may be done with a concave glass1 which1 however1 should not be ground thin like common eye-glasses1 but must have some substance4 ,in order1 however1 to make this experiment at once with the convex glass1 let a smaller black disk be inserted within the light disk on a black ground4 ,if we magnify the black disk on a white ground with a convex glass1 the same result takes place as if we diminished the white disk2 for we extend the black outline upon the white1 and we thus perceive the yellow edge together with the blue edge 7,d74 #bja4 ,these two appearances1 the blue and yellow1 exhibit themselves in and upon the white3 they both assume a reddish hue1 in proportion as they mingle with the black4#b ,illustration #bjb4 ,in this short statement we have described the primordial phenomena of all appearance of colour occasioned by refraction4 ,these undoubtedly may be repeated1 varied1 and rendered more striking2 may be combined1 complicated1 confused2 but1 after all1 may be still restored to their original simplicity4 #bjc4 ,in examining the process of the experiment just given1 we find that in the one case we have1 to appearance1 extended the white edge upon the dark surface2 in the other we have extended the dark edge upon the white surface1 supplanting one by the other1 pushing one over the other4 ,we will now endeavour1 step by step1 to analyse these and similar cases4 #bjd4 ,if we cause the white disk to move1 in appearance1 entirely from its place1 which can be done effectually by prisms1 it will be coloured according to the direction in which it apparently moves1 in conformity with the above laws4 ,if we look at the disk a#c through a prism1 so that it appear moved to b1 the outer edge will appear blue and blue-red1 according to the law of the figure ,b 7fig4 #a71 the other edge being yellow1 and yellow-red1 according to the law of the figure ,c 7fig4 #a74 ,for in the first case the white figure is1 as it were1 extended over the dark boundary1 and in the other case the dark boundary is passed over the white figure4 ,the same happens if the disk is1 to appearance1 moved from a to c1 from a to d1 and so throughout the circle4 #bje4 ,as it is with the simple effect1 so it is with more complicated appearances4 ,if we look through a horizontal prism 7a b#d7 at a white disk placed at some distance behind it at e1 the disk will be raised to f1 and coloured according to the above law4 ,if we remove this prism1 and look through a vertical one 7c d7 at the same disk1 it will appear at h1 and coloured according to the same law4 ,if we place the two prisms one upon the other1 the disk will appear displaced diagonally1 in conformity with a general law of nature1 and will be coloured as before2 that is1 according to its movement in the direction1 e4g43#e #bjf4 ,if we attentively examine these opposite coloured edges1 we find that they only appear in the direction of the apparent change of place4 ,a round figure leaves us in some degree uncertain as to this3 a quadrangular figure removes all doubt4 #bjg4 ,the quadrangular figure a1#f moved in the direction a b or a d exhibits no colour on the sides which are parallel with the direction in which it moves3 on the other hand1 if moved in the direction a c1 parallel with its diagonal1 all the edges of the figure appear coloured4#g #bjh4 ,thus1 a former position 7#bjc7 is here confirmed2 viz4 to produce colour1 an object must be so displaced that the light edges be apparently carried over a dark surface1 the dark edges over a light surface1 the figure over its boundary1 the boundary over the figure4 ,but if the rectilinear boundaries of a figure could be indefinitely extended by refraction1 so that figure and background might only pursue their course next1 but not over each other1 no colour would appear1 not even if they were prolonged to infinity4 #a ,plate #b1 fig4 #a4 #b ,the author has omitted the orange and purple in the coloured diagrams which illustrate these first experiments1 from a wish probably to present the elementary contrast1 on which he lays a stress1 in greater simplicity4 ,the reddish tinge would be apparent1 as stated above1 where the blue and yellow are in contact with the black4--,t4 #c ,plate #b1 fig4 #b #d ,plate #b1 fig4 #d #e ,in this case1 according to the author1 the refracting medium being increased in mass1 the appearance of colour is increased1 and the displacement is greater4--,t4 #f ,plate #b1 fig4 #c4 #g ,fig4 #b1 plate #a1 contains a variety of forms1 which1 when viewed through a prism1 are intended to illustrate the statement in this and the following paragraph4 ,,xiv4 ,,conditions ,,under ,,which ,,the ,,appearance ,,of ,,colour ,,increases4 #bji4 ,we have seen in the foregoing experiments that all appearance of colour occasioned by refraction depends on the condition that the boundary or edge be moved in upon the object itself1 or the object itself over the ground1 that the figure should be1 as it were1 carried over itself1 or over the ground4 ,and we shall now find that1 by increased displacement of the object1 the appearance of colour exhibits itself in a greater degree4 ,this takes place in subjective experiments1 to which1 for the present1 we confine ourselves1 under the following conditions4 #baj4 ,first1 if1 in looking through parallel mediums1 the eye is directed more obliquely4 ,secondly1 if the surfaces of the medium are no longer parallel1 but form a more or less acute angle4 ,thirdly1 owing to the increased proportion of the medium1 whether parallel mediums be increased in size1 or whether the angle be increased1 provided it does not attain a right angle4 ,fourthly1 owing to the distance of the eye armed with a refracting medium from the object to be displaced4 ,fifthly1 owing to a chemical property that may be communicated to the glass1 and which may be afterwards increased in effect4 #baa4 ,the greatest change of place1 short of considerable distortion of the object1 is produced by means of prisms1 and this is the reason why the appearance of colour can be exhibited most powerfully through glasses of this form4 ,yet we will not1 in employing them1 suffer ourselves to be dazzled by the splendid appearances they exhibit1 but keep the above well-established1 simple principles calmly in view4 #bab4 ,the colour which is outside1 or foremost1 in the apparent change of an object by refraction1 is always the broader1 and we will henceforth call this a border3 the colour that remains next the outline is the narrower1 and this we will call an edge4 #bac4 ,if we move a dark boundary towards a light surface1 the yellow broader border is foremost1 and the narrower yellow-red edge follows close to the outline4 ,if we move a light boundary towards a dark surface1 the broader violet border is foremost1 and the narrower blue edge follows4 #bad4 ,if the object is large1 its centre remains uncoloured4 ,its inner surface is then to be considered as unlimited 7#aie73 it is displaced1 but not otherwise altered3 but if the object is so narrow1 that under the above conditions the yellow border can reach the blue edge1 the space between the outlines will be entirely covered with colour4 ,if we make this experiment with a white stripe on a black ground1#a the two extremes will presently meet1 and thus produce green4 ,we shall then see the following series of colours3-- ,yellow-red4 ,yellow4 ,green4 ,blue4 ,blue-red4 #bae4 ,if we place a black band1 or stripe1 on white paper1#b the violet border will spread till it meets the yellow-red edge4 ,in this case the intermediate black is effaced 7as the intermediate white was in the last experiment71 and in its stead a splendid pure red will appear4#c ,the series of colours will now be as follows3-- ,blue4 ,blue-red4 ,red4 ,yellow-red4 ,yellow4 #baf4 ,the yellow and blue1 in the first case 7#bad71 can by degrees meet so fully1 that the two colours blend entirely in green1 and the order will then be1 ,yellow-red4 ,green4 ,blue-red4 ,in the second case 7#bae71 under similar circumstances1 we see only ,blue4 ,red4 ,yellow4 ,this appearance is best exhibited by refracting the bars of a window when they are relieved on a grey sky4#d #bag4 ,in all this we are never to forget that this appearance is not to be considered as a complete or final state1 but always as a progressive1 increasing1 and1 in many senses1 controllable appearance4 ,thus we find that1 by the negation of the above five conditions1 it gradually decreases1 and at last disappears altogether4 #a ,plate #b1 fig4 #e1 left4 #b ,plate #b1 fig4 #e1 right4 #c ,this pure red1 the union of orange and violet1 is considered by the author the maximum of the coloured appearance3 he has appropriated the term purpur to it4 ,see paragraph #gjc1 and note4--,t4 #d ,the bands or stripes in fig4 #d1 plate #a1 when viewed through a prism1 exhibit the colours represented in plate #b1 fig4 #e4 ,,xv4 ,,explanation ,,of ,,the ,,foregoing ,,phenomena4 #bah4 ,before we proceed further1 it is incumbent on us to explain the first tolerably simple phenomenon1 and to show its connexion with the principles first laid down1 in order that the observer of nature may be enabled clearly to comprehend the more complicated appearances that follow4 #bai4 ,in the first place1 it is necessary to remember that we have to do with circumscribed objects4 ,in the act of seeing1 generally1 it is the circumscribed visible which chiefly invites our observation2 and in the present instance1 in speaking of the appearance of colour1 as occasioned by refraction1 the circumscribed visible1 the detached object solely occupies our attention4 #bbj4 ,for our chromatic exhibitions we can1 however1 divide objects generally into primary and secondary4 ,the expressions of themselves denote what we understand by them1 but our meaning will be rendered still more plain by what follows4 #bba4 ,primary objects may be considered firstly as original1 as images which are impressed on the eye by things before it1 and which assure us of their reality4 ,to these the secondary images may be opposed as derived images1 which remain in the organ when the object itself is taken away2 those apparent after-images1 which have been circumstantially treated of in the doctrine of physiological colours4 #bbb4 ,the primary images1 again1 may be considered as direct images1 which1 like the original impressions1 are conveyed immediately from the object to the eye4 ,in contradistinction to these1 the secondary images may be considered as indirect1 being only conveyed to us1 as it were1 at second-hand from a reflecting surface4 ,these are the mirrored1 or catoptrical1 images1 which in certain cases can also become double images3 #bbc4 ,when1 namely1 the reflecting body is transparent1 and has two parallel surfaces1 one behind the other3 in such a case1 an image may be reflected to the eye from both surfaces1 and thus arise double images1 inasmuch as the upper image does not quite cover the under one3 this may take place in various ways4 ,let a playing-card be held before a mirror4 ,we shall at first see the distinct image of the card1 but the edge of the whole card1 as well as that of every spot upon it1 will be bounded on one side with a border1 which is the beginning of the second reflection4 ,this effect varies in different mirrors1 according to the different thickness of the glass1 and the accidents of polishing4 ,if a person wearing a white waistcoat1 with the remaining part of his dress dark1 stands before certain mirrors1 the border appears very distinctly1 and in like manner the metal buttons on dark cloth exhibit the double reflection very evidently4 #bbd4 ,the reader who has made himself acquainted with our former descriptions of experiments 7#hj7 will the more readily follow the present statement4 ,the window-bars reflected by plates of glass appear double1 and by increased thickness of the glass1 and a due adaptation of the angle of reflection1 the two reflections may be entirely separated from each other4 ,so a vase full of water1 with a plane mirror-like bottom1 reflects any object twice1 the two reflections being more or less separated under the same conditions4 ,in these cases it is to be observed that1 where the two reflections cover each other1 the perfect vivid image is reflected1 but where they are separated they exhibit only weak1 transparent1 and shadowy images4 #bbe4 ,if we wish to know which is the under and which the upper image1 we have only to take a coloured medium1 for then a light object reflected from the under surface is of the colour of the medium1 while that reflected from the upper surface presents the complemental colour4 ,with dark objects it is the reverse2 hence black and white surfaces may be here also conveniently employed4 ,how easily the double images assume and evoke colours will here again be striking4 #bbf4 ,thirdly1 the primary images may be considered as principal images1 while the secondary can be1 as it were1 annexed to these as accessory images4 ,such an accessory image produces a sort of double form2 except that it does not separate itself from the principal object1 although it may be said to be always endeavouring to do so4 ,it is with secondary images of this last description that we have to do in prismatic appearances4 #bbg4 ,a surface without a boundary exhibits no appearance of colour when refracted 7#aie74 ,whatever is seen must be circumscribed by an outline to produce this effect4 ,in other words a figure1 an object1 is required2 this object undergoes an apparent change of place by refraction3 the change is however not complete1 not clean1 not sharp2 but incomplete1 inasmuch as an accessory image only is produced4 #bbh4 ,in examining every appearance of nature1 but especially in examining an important and striking one1 we should not remain in one spot1 we should not confine ourselves to the insulated fact1 nor dwell on it exclusively1 but look round through all nature to see where something similar1 something that has affinity to it1 appears3 for it is only by combining analogies that we gradually arrive at a whole which speaks for itself1 and requires no further explanation4 #bbi4 ,thus we here call to mind that in certain cases refraction unquestionably produces double images1 as is the case in ,iceland spar3 similar double images are also apparent in cases of refraction through large rock crystals1 and in other instances2 phenomena which have not hitherto been sufficiently observed4#a #bcj4 ,but since in the case under consideration 7#bbg7 the question relates not to double but to accessory images1 we refer to a phenomenon already adverted to1 but not yet thoroughly investigated4 ,we allude to an earlier experiment1 in which it appeared that a sort of conflict took place in regard to the retina between a light object and its dark ground1 and between a dark object and its light ground 7#af74 ,the light object in this case appeared larger1 the dark one smaller4 #bca4 ,by a more exact observation of this phenomenon we may remark that the forms are not sharply distinguished from the ground1 but that they appear with a kind of grey1 in some degree1 coloured edge2 in short1 with an accessory image4 ,if1 then1 objects seen only with the naked eye produce such effects1 what may not take place when a dense medium is interposed8 ,it is not that alone which presents itself to us in obvious operation which produces and suffers effects1 but likewise all principles that have a mutual relation only of some sort are efficient accordingly1 and indeed often in a very high degree4 #bcb4 ,thus when refraction produces its effect on an object there appears an accessory image next the object itself3 the real form thus refracted seems even to linger behind1 as if resisting the change of place2 but the accessory image seems to advance1 and extends itself more or less in the mode already shown 7#bab-baf74 #bcc4 ,we also remarked 7#bbd7 that in double images the fainter appear only half substantial1 having a kind of transparent1 evanescent character1 just as the fainter shades of double shadows must always appear as half-shadows4 ,these latter assume colours easily1 and produce them readily 7#fi71 the former also 7#hj72 and the same takes place in the instance of accessory images1 which1 it is true1 do not altogether quit the real object1 but still advance or extend from it as half-substantial images1 and hence can appear coloured so quickly and so powerfully4 #bcd4 ,that the prismatic appearance is in fact an accessory image we may convince ourselves in more than one mode4 ,it corresponds exactly with the form of the object itself4 ,whether the object be bounded by a straight line or a curve1 indented or waving1 the form of the accessory image corresponds throughout exactly with the form of the object4#b #bce4 ,again1 not only the form but other qualities of the object are communicated to the accessory image4 ,if the object is sharply relieved from its ground1 like white on black1 the coloured accessory image in like manner appears in its greatest force4 ,it is vivid1 distinct1 and powerful2 but it is most especially powerful when a luminous object is shown on a dark ground1 which may be contrived in various ways4 #bcf4 ,but if the object is but faintly distinguished from the ground1 like grey objects on black or white1 or even on each other1 the accessory image is also faint1 and1 when the original difference of tint or force is slight1 becomes hardly discernible4 #bcg4 ,the appearances which are observable when coloured objects are relieved on light1 dark1 or coloured grounds are1 moreover1 well worthy of attention4 ,in this case a union takes place between the apparent colour of the accessory image and the real colour of the object2 a compound colour is the result1 which is either assisted and enhanced by the accordance1 or neutralised by the opposition of its ingredients4 #bch4 ,but the common and general characteristic both of the double and accessory image is semi-transparence4 ,the tendency of a transparent medium to become only half transparent1 or merely light-transmitting1 has been before adverted to 7#adg1 #adh74 ,let the reader assume that he sees within or through such a medium a visionary image1 and he will at once pronounce this latter to be a semi-transparent image4 #bci4 ,thus the colours produced by refraction may be fitly explained by the doctrine of the semi-transparent mediums4 ,for where dark passes over light1 as the border of the semi-transparent accessory image advances1 yellow appears2 and1 on the other hand1 where a light outline passes over the dark background1 blue appears 7#aej1 #aea74 #bdj4 ,the advancing foremost colour is always the broader4 ,thus the yellow spreads over the light with a broad border1 but the yellow-red appears as a narrower stripe and is next the dark1 according to the doctrine of augmentation1 as an effect of shade4#c #bda4 ,on the opposite side the condensed blue is next the edge1 while the advancing border1 spreading as a thinner veil over the black1 produces the violet colour1 precisely on the principles before explained in treating of semi-transparent mediums1 principles which will hereafter be found equally efficient in many other cases4 #bdb4 ,since an analysis like the present requires to be confirmed by ocular demonstration1 we beg every reader to make himself acquainted with the experiments hitherto adduced1 not in a superficial manner1 but fairly and thoroughly4 ,we have not placed arbitrary signs before him instead of the appearances themselves2 no modes of expression are here proposed for his adoption which may be repeated for ever without the exercise of thought and without leading any one to think2 but we invite him to examine intelligible appearances1 which must be present to the eye and mind1 in order to enable him clearly to trace these appearances to their origin1 and to explain them to himself and to others4 #a ,the date of the publication1 #ahaj1 is sometimes to be remembered4--,t4 #b ,the forms in fig4 #b1 plate #a1 when seen through a prism1 are again intended to exemplify this4 ,in the plates to the original work curvilinear figures are added1 but the circles1 fig4 #a1 in the same plate1 may answer the same end4--,t4 #c ,the author has before observed that colour is a degree of darkness1 and he here means that increase of darkness1 produced by transparent mediums1 is1 to a certain extent1 increase of colour4--,t4 ,,xvi4 ,,decrease ,,of ,,the ,,appearance ,,of ,,colour4 #bdc4 ,we need only take the five conditions 7#baj7 under which the appearance of colour increases in the contrary order1 to produce the contrary or decreasing state2 it may be as well1 however1 briefly to describe and review the corresponding modifications which are presented to the eye4 #bdd4 ,at the highest point of complete junction of the opposite edges1 the colours appear as follows 7#baf73-- ,yellow-red4 ,blue4 ,green4 ,red4 ,blue-red4 ,yellow4 #bde4 ,where the junction is less complete1 the appearance is as follows 7#bad1 #bae73-- ,yellow-red4 ,blue4 ,yellow4 ,blue-red4 ,green4 ,red4 ,blue4 ,yellow-red4 ,blue-red4 ,yellow4 ,here1 therefore1 the surface still appears completely coloured1 but neither series is to be considered as an elementary series1 always developing itself in the same manner and in the same degrees2 on the contrary1 they can and should be resolved into their elements2 and1 in doing this1 we become better acquainted with their nature and character4 #bdf4 ,these elements then are 7#aii1 #bjj1 #bja7-- ,yellow-red4 ,blue4 ,yellow4 ,blue-red4 ,white4 ,black4 ,blue4 ,yellow-red4 ,blue-red4 ,yellow4 ,here the surface itself1 the original object1 which has been hitherto completely covered1 and as it were lost1 again appears in the centre of the colours1 asserts its right1 and enables us fully to recognise the secondary nature of the accessory images which exhibit themselves as edges and borders4--,note ,n4 #bdg4 ,we can make these edges and borders as narrow as we please2 nay1 we can still have refraction in reserve after having done away with all appearance of colour at the boundary of the object4 ,having now sufficiently investigated the exhibition of colour in this phenomenon1 we repeat that we cannot admit it to be an elementary phenomenon4 ,on the contrary1 we have traced it to an antecedent and a simpler one2 we have derived it1 in connexion with the theory of secondary images1 from the primordial phenomenon of light and darkness1 as affected or acted upon by semi-transparent mediums4 ,thus prepared1 we proceed to describe the appearances which refraction produces on grey and coloured objects1 and this will complete the section of subjective phenomena4 ,,xvii4 ,,grey ,,objects ,,displaced ,,by ,,refraction4 #bdh4 ,hitherto we have confined our attention to black and white objects relieved on respectively opposite grounds1 as seen through the prism1 because the coloured edges and borders are most clearly displayed in such cases4 ,we now repeat these experiments with grey objects1 and again find similar results4 #bdi4 ,as we called black the equivalent of darkness1 and white the representative of light 7#ah71 so we now venture to say that grey represents half-shadow1 which partakes more or less of light and darkness1 and thus stands between the two4 ,we invite the reader to call to mind the following facts as bearing on our present view4 #bej4 ,grey objects appear lighter on a black than on a white ground 7#cc72 they appear as a light on a black ground1 and larger2 as a dark on the white ground1 and smaller4 7#af47 #bea4 ,the darker the grey the more it appears as a faint light on black1 as a strong dark on white1 and vice vers2 hence the accessory images of dark-grey on black are faint1 on white strong3 so the accessory images of light-grey on white are faint1 on black strong4 #beb4 ,grey on black1 seen through the prism1 will exhibit the same appearances as white on black2 the edges are coloured according to the same law1 only the borders appear fainter4 ,if we relieve grey on white1 we have the same edges and borders which would be produced if we saw black on white through the prism4--,note ,o4 #bec4 ,various shades of grey placed next each other in gradation will exhibit at their edges1 either blue and violet only1 or red and yellow only1 according as the darker grey is placed over or under4 #bed4 ,a series of such shades of grey placed horizontally next each other will be coloured conformably to the same law according as the whole series is relieved1 on a black or white ground above or below4 #bee4 ,the observer may see the phenomena exhibited by the prism at one glance1 by enlarging the plate intended to illustrate this section4#a #bef4 ,it is of great importance duly to examine and consider another experiment in which a grey object is placed partly on a black and partly on a white surface1 so that the line of division passes vertically through the object4 #beg4 ,the colours will appear on this grey object in conformity with the usual law1 but according to the opposite relation of the light to the dark1 and will be contrasted in a line4 ,for as the grey is as a light to the black1 so it exhibits the red and yellow above the blue and violet below3 again1 as the grey is as a dark to the white1 the blue and violet appear above the red and yellow below4 ,this experiment will be found of great importance with reference to the next chapter4 #a ,it has been thought unnecessary to give all the examples in the plate alluded to1 but the leading instance referred to in the next paragraph will be found in plate #c1 fig4 #a4 ,the grey square when seen through a prism will exhibit the effects described in par4 #beg4--,t4 ,,xviii4 ,,coloured ,,objects ,,displaced ,,by ,,refraction4 #beh4 ,an unlimited coloured surface exhibits no prismatic colour in addition to its own hue1 thus not at all differing from a black1 white1 or grey surface4 ,to produce the appearance of colour1 light and dark boundaries must act on it either accidentally or by contrivance4 ,hence experiments and observations on coloured surfaces1 as seen through the prism1 can only be made when such surfaces are separated by an outline from another differently tinted surface1 in short when circumscribed objects are coloured4 #bei4 ,all colours1 whatever they may be1 correspond so far with grey1 that they appear darker than white and lighter than black4 ,this shade-like quality of colour 77 has been already alluded to 7#fi71 and will become more and more evident4 ,if then we begin by placing coloured objects on black and white surfaces1 and examine them through the prism1 we shall again have all that we have seen exhibited with grey surfaces4 ,illustration #bfj4 ,if we displace a coloured object by refraction1 there appears1 as in the case of colourless objects and according to the same laws1 an accessory image4 ,this accessory image retains1 as far as colour is concerned1 its usual nature1 and acts on one side as a blue and blue-red1 on the opposite side as a yellow and yellow-red4 ,hence the apparent colour of the edge and border will be either homogeneous with the real colour of the object1 or not so4 ,in the first case the apparent image identifies itself with the real one1 and appears to increase it1 while1 in the second case1 the real image may be vitiated1 rendered indistinct1 and reduced in size by the apparent image4 ,we proceed to review the cases in which these effects are most strikingly exhibited4 #bfa4 ,if we take a coloured drawing enlarged from the plate1 which illustrates this experiment#a1 and examine the red and blue squares placed next each other on a black ground1 through the prism as usual1 we shall find that as both colours are lighter than the ground1 similarly coloured edges and borders will appear above and below1 at the outlines of both1 only they will not appear equally distinct to the eye4 #bfb4 ,red is proportionally much lighter on black than blue is4 ,the colours of the edges will therefore appear stronger on the red than on the blue1 which here acts as a dark-grey1 but little different from black4 7#bea47 #bfc4 ,the extreme red edge will identify itself with the vermilion colour of the square1 which will thus appear a little elongated in this direction2 while the yellow border immediately underneath it only gives the red surface a more brilliant appearance1 and is not distinguished without attentive observation4 #bfd4 ,on the other hand the red edge and yellow border are heterogeneous with the blue square2 a dull red appears at the edge1 and a dull green mingles with the figure1 and thus the blue square seems1 at a hasty glance1 to be comparatively diminished on this side4 #bfe4 ,at the lower outline of the two squares a blue edge and a violet border will appear1 and will produce the contrary effect2 for the blue edge1 which is heterogeneous with the warm red surface1 will vitiate it and produce a neutral colour1 so that the red on this side appears comparatively reduced and driven upwards1 and the violet border on the black is scarcely perceptible4 #bff4 ,on the other hand1 the blue apparent edge will identify itself with the blue square1 and not only not reduce1 but extend it4 ,the blue edge and even the violet border next it have the apparent effect of increasing the surface1 and elongating it in that direction4 #bfg4 ,the effect of homogeneous and heterogeneous edges1 as ,i have now minutely described it1 is so powerful and singular that the two squares at the first glance seem pushed out of their relative horizontal position and moved in opposite directions1 the red upwards1 the blue downwards4 ,but no one who is accustomed to observe experiments in a certain succession1 and respectively to connect and trace them1 will suffer himself to be deceived by such an unreal effect4 #bfh4 ,a just impression with regard to this important phenomenon will1 however1 much depend on some nice and even troublesome conditions1 which are necessary to produce the illusion in question4 ,paper should be tinged with vermilion or the best minium for the red square1 and with deep indigo for the blue square4 ,the blue and red prismatic edges will then unite imperceptibly with the real surfaces where they are respectively homogeneous2 where they are not1 they vitiate the colours of the squares without producing a very distinct middle tint4 ,the real red should not incline too much to yellow1 otherwise the apparent deep red edge above will be too distinct2 at the same time it should be somewhat yellow1 otherwise the transition to the yellow border will be too observable4 ,the blue must not be light1 otherwise the red edge will be visible1 and the yellow border will produce a too decided green1 while the violet border underneath would not give us the impression of being part of an elongated light blue square4 #bfi4 ,all this will be treated more circumstantially hereafter1 when we speak of the apparatus intended to facilitate the experiments connected with this part of our subject4#b ,every inquirer should prepare the figures himself1 in order fairly to exhibit this specimen of ocular deception1 and at the same time to convince himself that the coloured edges1 even in this case1 cannot escape accurate examination4 #bgj4 ,meanwhile various other combinations1 as exhibited in the plate1 are fully calculated to remove all doubt on this point in the mind of every attentive observer4 #bga4 ,if1 for instance1 we look at a white square1 next the blue one1 on a black ground1 the prismatic hues of the opposite edges of the white1 which here occupies the place of the red in the former experiment1 will exhibit themselves in their utmost force4 ,the red edge extends itself above the level of the blue almost in a greater degree than was the case with the red square itself in the former experiment4 ,the lower blue edge1 again1 is visible in its full force next the white1 while1 on the other hand1 it cannot be distinguished next the blue square4 ,the violet border underneath is also much more apparent on the white than on the blue4 #bgb4 ,if the observer now compares these double squares1 carefully prepared and arranged one above the other1 the red with the white1 the two blue squares together1 the blue with the red1 the blue with the white1 he will clearly perceive the relations of these surfaces to their coloured edges and borders4 #bgc4 ,the edges and their relations to the coloured surfaces appear still more striking if we look at the coloured squares and a black square on a white ground2 for in this case the illusion before mentioned ceases altogether1 and the effect of the edges is as visible as in any case that has come under our observation4 ,let the blue and red squares be first examined through the prism4 ,in both the blue edge now appears above2 this edge1 homogeneous with the blue surface1 unites with it1 and appears to extend it upwards1 only the blue edge1 owing to its lightness1 is somewhat too distinct in its upper portion2 the violet border underneath it is also sufficiently evident on the blue4 ,the apparent blue edge is1 on the other hand1 heterogeneous with the red square2 it is neutralised by contrast1 and is scarcely visible2 meanwhile the violet border1 uniting with the real red1 produces a hue resembling that of the peach-blossom4 #bgd4 ,if thus1 owing to the above causes1 the upper outlines of these squares do not appear level with each other1 the correspondence of the under outlines is the more observable2 for since both colours1 the red and the blue1 are darks compared with the white 7as in the former case they were light compared with the black71 the red edge with its yellow border appears very distinctly under both4 ,it exhibits itself under the warm red surface in its full force1 and under the dark blue nearly as it appears under the black3 as may be seen if we compare the edges and borders of the figures placed one above the other on the white ground4 #bge4 ,in order to present these experiments with the greatest variety and perspicuity1 squares of various colours are so arranged#c that the boundary of the black and white passes through them vertically4 ,according to the laws now known to us1 especially in their application to coloured objects1 we shall find the squares as usual doubly coloured at each edge2 each square will appear to be split in two1 and to be elongated upwards or downwards4 ,we may here call to mind the experiment with the grey figure seen in like manner on the line of division between black and white 7#beg74d #bgf4 ,a phenomenon was before exhibited1 even to illusion1 in the instance of a red and blue square on a black ground2 in the present experiment the elongation upwards and downwards of two differently coloured figures is apparent in the two halves of one and the same figure of one and the same colour4 ,thus we are still referred to the coloured edges and borders1 and to the effects of their homogeneous and heterogeneous relations with respect to the real colours of the objects4 #bgg4 ,i leave it to observers themselves to compare the various gradations of coloured squares1 placed half on black half on white1 only inviting their attention to the apparent alteration which takes place in contrary directions2 for red and yellow appear elongated upwards if on a black ground1 downwards if on a white2 blue1 downwards if on a black ground1 upwards if on a white4 ,all which1 however1 is quite in accordance with the diffusely detailed examples above given4 #bgh4 ,let the observer now turn the figures so that the before-mentioned squares placed on the line of division between black and white may be in a horizontal series2 the black above1 the white underneath4 ,on looking at these squares through the prism1 he will observe that the red square gains by the addition of two red edges2 on more accurate examination he will observe the yellow border on the red figure1 and the lower yellow border upon the white will be perfectly apparent4 #bgi4 ,the upper red edge on the blue square is on the other hand hardly visible2 the yellow border next it produces a dull green by mingling with the figure2 the lower red edge and the yellow border are displayed in lively colours4 #bhj4 ,after observing that the red figure in these cases appears to gain by an addition on both sides1 while the dark blue1 on one side at least1 loses something2 we shall see the contrary effect produced by turning the same figures upside down1 so that the white ground be above1 the black below4 #bha4 ,for as the homogeneous edges and borders now appear above and below the blue square1 this appears elongated1 and a portion of the surface itself seems even more brilliantly coloured3 it is only by attentive observation that we can distinguish the edges and borders from the colour of the figure itself4 #bhb4 ,the yellow and red squares1 on the other hand1 are comparatively reduced by the heterogeneous edges in this position of the figures1 and their colours are1 to a certain extent1 vitiated4 ,the blue edge in both is almost invisible4 ,the violet border appears as a beautiful peach-blossom hue on the red1 as a very pale colour of the same kind on the yellow2 both the lower edges are green2 dull on the red1 vivid on the yellow2 the violet border is but faintly perceptible under the red1 but is more apparent under the yellow4 #bhc4 ,every inquirer should make it a point to be thoroughly acquainted with all the appearances here adduced1 and not consider it irksome to follow out a single phenomenon through so many modifying circumstances4 ,these experiments1 it is true1 may be multiplied to infinity by differently coloured figures1 upon and between differently coloured grounds4 ,under all such circumstances1 however1 it will be evident to every attentive observer that coloured squares only appear relatively altered1 or elongated1 or reduced by the prism1 because an addition of homogeneous or heterogeneous edges produces an illusion4 ,the inquirer will now be enabled to do away with this illusion if he has the patience to go through the experiments one after the other1 always comparing the effects together1 and satisfying himself of their correspondence4 ,experiments with coloured objects might have been contrived in various ways3 why they have been exhibited precisely in the above mode1 and with so much minuteness1 will be seen hereafter4 ,the phenomena1 although formerly not unknown1 were much misunderstood2 and it was necessary to investigate them thoroughly to render some portions of our intended historical view clearer4 #bhd4 ,in conclusion1 we will mention a contrivance by means of which our scientific readers may be enabled to see these appearances distinctly at one view1 and even in their greatest splendour4 ,cut in a piece of pasteboard five perfectly similar square openings of about an inch1 next each other1 exactly in a horizontal line3 behind these openings place five coloured glasses in the natural order1 orange1 yellow1 green1 blue1 violet4 ,let the series thus adjusted be fastened in an opening of the camera obscura1 so that the bright sky may be seen through the squares1 or that the sun may shine on them2 they will thus appear very powerfully coloured4 ,let the spectator now examine them through the prism1 and observe the appearances1 already familiar by the foregoing experiments1 with coloured objects1 namely1 the partly assisting1 partly neutralising effects of the edges and borders1 and the consequent apparent elongation or reduction of the coloured squares with reference to the horizontal line4 ,the results witnessed by the observer in this case1 entirely correspond with those in the cases before analysed2 we do not1 therefore1 go through them again in detail1 especially as we shall find frequent occasions hereafter to return to the subject4--,note ,p4 #a ,plate #c1 fig4 #a4 ,the author always recommends making the experiments on an increased scale1 in order to see the prismatic effects distinctly4 #b ,neither the description of the apparatus nor the recapitulation of the whole theory1 so often alluded to by the author1 were ever given4--,t4 #c ,plate #c4 fig4 #a4 #d ,the grey square is introduced in the same plate1 fig4 #a1 above the coloured squares4 ,,xix4 ,,achromatism ,,and ,,hyperchromatism4 #bhe4 ,formerly when much that is regular and constant in nature was considered as mere aberration and accident1 the colours arising from refraction were but little attended to1 and were looked upon as an appearance attributable to particular local circumstances4 #bhf4 ,but after it had been assumed that this appearance of colour accompanies refraction at all times1 it was natural that it should be considered as intimately and exclusively connected with that phenomenon2 the belief obtaining that the measure of the coloured appearance was in proportion to the measure of the refraction1 and that they must advance pari passu with each other4 #bhg4 ,if1 again1 philosophers ascribed the phenomenon of a stronger or weaker refraction1 not indeed wholly1 but in some degree1 to the different density of the medium1 7as purer atmospheric air1 air charged with vapours1 water1 glass1 according to their increasing density1 increase the so-called refraction1 or displacement of the object27 so they could hardly doubt that the appearance of colour must increase in the same proportion2 and hence took it for granted1 in combining different mediums which were to counteract refraction1 that as long as refraction existed1 the appearance of colour must take place1 and that as soon as the colour disappeared1 the refraction also must cease4 #bhh4 ,afterwards it was1 however1 discovered that this relation which was assumed to correspond1 was1 in fact1 dissimilar2 that two mediums can refract an object with equal power1 and yet produce very dissimilar coloured borders4 #bhi4 ,it was found that1 in addition to the physical principle to which refraction was ascribed1 a chemical one was also to be taken into the account4 ,we propose to pursue this subject hereafter1 in the chemical division of our inquiry1 and we shall have to describe the particulars of this important discovery in our history of the doctrine of colours4 ,what follows may suffice for the present4 #bij4 ,in mediums of similar or nearly similar refracting power1 we find the remarkable circumstance that a greater and lesser appearance of colour can be produced by a chemical treatment2 the greater effect is owing1 namely1 to acids1 the lesser to alkalis4 ,if metallic oxydes are introduced into a common mass of glass1 the coloured appearance through such glasses becomes greatly increased without any perceptible change of refracting power4 ,that the lesser effect1 again1 is produced by alkalis1 may be easily supposed4 #bia4 ,those kinds of glass which were first employed after the discovery1 are called flint and crown glass2 the first produces the stronger1 the second the fainter appearance of colour4 #bib4 ,we shall make use of both these denominations as technical terms in our present statement1 and assume that the refractive power of both is the same1 but that flint-glass produces the coloured appearance more strongly by one-third than the crown-glass4 ,the diagram 7,plate #c1 fig4 #b17 may serve in illustration4 #bic4 ,a black surface is here divided into compartments for more convenient demonstration3 let the spectator imagine five white squares between the parallel lines a1 b1 and c1 d4 ,the square ,no4 #a1 is presented to the naked eye unmoved from its place4 #bid4 ,but let the square ,no4 #b1 seen through a crown-glass prism g1 be supposed to be displaced by refraction three compartments1 exhibiting the coloured borders to a certain extent2 again1 let the square ,no4 #c1 seen through a flint glass prism h1 in like manner be moved downwards three compartments1 when it will exhibit the coloured borders by about a third wider than ,no4 #b4 #bie4 ,again1 let us suppose that the square ,no4 #d1 has1 like ,no4 #b1 been moved downwards three compartments by a prism of crown-glass1 and that then by an oppositely placed prism h1 of flint-glass1 it has been again raised to its former situation1 where it now stands4 #bif4 ,here1 it is true1 the refraction is done away with by the opposition of the two2 but as the prism h1 in displacing the square by refraction through three compartments1 produces coloured borders wider by a third than those produced by the prism g1 so1 notwithstanding the refraction is neutralised1 there must be an excess of coloured border remaining4 7,the position of this colour1 as usual1 depends on the direction of the apparent motion 7#bjd7 communicated to the square by the prism h1 and1 consequently1 it is the reverse of the appearance in the two squares #b and #c1 which have been moved in an opposite direction47 ,this excess of colour we have called ,hyperchromatism1 and from this the achromatic state may be immediately arrived at4 #big4 ,for assuming that it was the square ,no4 #e which was removed three compartments from its first supposed place1 like ,no4 #b1 by a prism of crown-glass g1 it would only be necessary to reduce the angle of a prism of flint-glass h1 and to connect it1 reversed1 to the prism g1 in order to raise the square ,no4 #e two degrees or compartments2 by which means the ,hyperchromatism of the first case would cease1 the figure would not quite return to its first position1 and yet be already colourless4 ,the prolonged lines of the united prisms1 under ,no4 #e1 show that a single complete prism remains3 again1 we have only to suppose the lines curved1 and an object-glass presents itself4 ,such is the principle of the achromatic telescopes4 #bih4 ,for these experiments1 a small prism composed of three different prisms1 as prepared in ,england1 is extremely well adapted4 ,it is to be hoped our own opticians will in future enable every friend of science to provide himself with this necessary instrument4 ,,xx4 ,,advantages ,,of ,,subjective ,,experiments4--,,transition ,,to ,,the ,,objective4 #bii4 ,we have presented the appearances of colour as exhibited by refraction1 first1 by means of subjective experiments2 and we have so far arrived at a definite result1 that we have been enabled to deduce the phenomena in question from the doctrine of semi-transparent mediums and double images4 #cjj4 ,in statements which have reference to nature1 everything depends on ocular inspection1 and these experiments are the more satisfactory as they may be easily and conveniently made4 ,every amateur can procure his apparatus without much trouble or cost1 and if he is a tolerable adept in pasteboard contrivances1 he may even prepare a great part of his machinery himself4 ,a few plain surfaces1 on which black1 white1 grey1 and coloured objects may be exhibited alternately on a light and dark ground1 are all that is necessary4 ,the spectator fixes them before him1 examines the appearances at the edge of the figures conveniently1 and as long as he pleases2 he retires to a greater distance1 again approaches1 and accurately observes the progressive states of the phenomena4 #cja4 ,besides this1 the appearances may be observed with sufficient exactness through small prisms1 which need not be of the purest glass4 ,the other desirable requisites in these glass instruments will1 however1 be pointed out in the section which treats of the apparatus4#a #cjb4 ,a great advantage in these experiments1 again1 is1 that they can be made at any hour of the day in any room1 whatever aspect it may have4 ,we have no need to wait for sunshine1 which in general is not very propitious to northern observers4 #a ,this description of the apparatus was never given4 ,,objective ,,experiments4 #cjc4 ,the objective experiments1 on the contrary1 necessarily require the sun-light which1 even when it is to be had1 may not always have the most desirable relation with the apparatus placed opposite to it4 ,sometimes the sun is too high1 sometimes too low1 and withal only a short time in the meridian of the best situated room4 ,it changes its direction during the observation1 the observer is forced to alter his own position and that of his apparatus1 in consequence of which the experiments in many cases become uncertain4 ,if the sun shines through the prism it exhibits all inequalities1 lines1 and bubbles in the glass1 and thus the appearance is rendered confused1 dim1 and discoloured4 #cjd4 ,yet both kinds of experiments must be investigated with equal accuracy4 ,they appear to be opposed to each other1 and yet are always parallel4 ,what one order of experiments exhibits the other exhibits likewise1 and yet each has its peculiar capabilities1 by means of which certain effects of nature are made known to us in more than one way4 #cje4 ,in the next place there are important phenomena which may be exhibited by the union of subjective and objective experiments4 ,the latter experiments again have this advantage1 that we can in most cases represent them by diagrams1 and present to view the component relations of the phenomena4 ,in proceeding1 therefore1 to describe the objective experiments1 we shall so arrange them that they may always correspond with the analogous subjective examples2 for this reason1 too1 we annex to the number of each paragraph the number of the former corresponding one4 ,but we set out by observing generally that the reader must consult the plates1 that the scientific investigator must be familiar with the apparatus in order that the twin-phenomena in one mode or the other may be placed before them4 ,,xxi4 ,,refraction ,,without ,,the ,,appearance ,,of ,,colour4 #cjf 7#aie1 #aif74 ,that refraction may exhibit its effects without producing an appearance of colour1 is not to be demonstrated so perfectly in objective as in subjective experiments4 ,we have1 it is true1 unlimited spaces which we can look at through the prism1 and thus convince ourselves that no colour appears where there is no boundary2 but we have no unlimited source of light which we can cause to act through the prism4 ,our light comes to us from circumscribed bodies2 and the sun1 which chiefly produces our prismatic appearances1 is itself only a small1 circumscribed1 luminous object4 #cjg4 ,we may1 however1 consider every larger opening through which the sun shines1 every larger medium through which the sun-light is transmitted and made to deviate from its course1 as so far unlimited that we can confine our attention to the centre of the surface without considering its boundaries4 #cjh 7#aig74 ,if we place a large water-prism in the sun1 a large bright space is refracted upwards by it on the plane intended to receive the image1 and the middle of this illumined space will be colourless4 ,the same effect may be produced if we make the experiment with glass prisms having angles of few degrees3 the appearance may be produced even through glass prisms1 whose refracting angle is sixty degrees1 provided we place the recipient surface near enough4 ,,xxii4 ,,conditions ,,of ,,the ,,appearance ,,of ,,colour4 #cji 7#aih74 ,although1 then1 the illumined space before mentioned appears indeed refracted and moved from its place1 but not coloured1 yet on the horizontal edges of this space we observe a coloured appearance4 ,that here again the colour is solely owing to the displacement of a circumscribed object may require to be more fully proved4 ,the luminous body which here acts is circumscribed3 the sun1 while it shines and diffuses light1 is still an insulated object4 ,however small the opening in the lid of a camera obscura be made1 still the whole image of the sun will penetrate it4 ,the light which streams from all parts of the sun's disk1 will cross itself in the smallest opening1 and form the angle which corresponds with the sun's apparent diameter4 ,on the outside we have a cone narrowing to the orifice2 within1 this apex spreads again1 producing on an opposite surface a round image1 which still increases in size in proportion to the distance of the recipient surface from the apex4 ,this image1 together with all other objects of the external landscape1 appears reversed on the white surface in question in a dark room4 #caj4 ,how little therefore we have here to do with single sun-rays1 bundles or fasces of rays1 cylinders of rays1 pencils1 or whatever else of the kind may be imagined1 is strikingly evident4 ,for the convenience of certain diagrams the sun-light may be assumed to arrive in parallel lines1 but it is known that this is only a fiction2 a fiction quite allowable where the difference between the assumption and the true appearance is unimportant2 but we should take care not to suffer such a postulate to be equivalent to a fact1 and proceed to further operations on such a fictitious basis4 #caa4 ,let the aperture in the window-shutter be now enlarged at pleasure1 let it be made round or square1 nay1 let the whole shutter be opened1 and let the sun shine into the room through the whole window2 the space which the sun illumines will always be larger according to the angle which its diameter makes2 and thus even the whole space illumined by the sun through the largest window is only the image of the sun plus the size of the opening4 ,we shall hereafter have occasion to return to this4 #cab 7#aii74 ,if we transmit the image of the sun through convex glasses we contract it towards the focus4 ,in this case1 according to the laws before explained1 a yellow border and a yellow-red edge must appear when the spectrum is thrown on white paper4 ,but as this experiment is dazzling and inconvenient1 it may be made more agreeably with the image of the full moon4 ,on contracting this orb by means of a convex glass1 the coloured edge appears in the greatest splendour2 for the moon transmits a mitigated light in the first instance1 and can thus the more readily produce colour which to a certain extent accompanies the subduing of light3 at the same time the eye of the observer is only gently and agreeably excited4 #cac 7#bjj74 ,if we transmit a luminous image through concave glasses1 it is dilated4 ,here the image appears edged with blue4 #cad4 ,the two opposite appearances may be produced by a convex glass1 simultaneously or in succession2 simultaneously by fastening an opaque disk in the centre of the convex glass1 and then transmitting the sun's image4 ,in this case the luminous image and the black disk within it are both contracted1 and1 consequently1 the opposite colours must appear4 ,again1 we can present this contrast in succession by first contracting the luminous image towards the focus1 and then suffering it to expand again beyond the focus1 when it will immediately exhibit a blue edge4 #cae 7#bja74 ,here too what was observed in the subjective experiments is again to be remarked1 namely1 that blue and yellow appear in and upon the white1 and that both assume a reddish appearance in proportion as they mingle with the black4 #caf 7#bjb1 #bjc74 ,these elementary phenomena occur in all subsequent objective experiments1 as they constituted the groundwork of the subjective ones4 ,the process too which takes place is the same2 a light boundary is carried over a dark surface1 a dark surface is carried over a light boundary4 ,the edges must advance1 and as it were push over each other in these experiments as in the former ones4 #cag 7#bjd74 ,if we admit the sun's image through a larger or smaller opening into the dark room1 if we transmit it through a prism so placed that its refracting angle1 as usual1 is underneath2 the luminous image1 instead of proceeding in a straight line to the floor1 is refracted upwards on a vertical surface placed to receive it4 ,this is the moment to take notice of the opposite modes in which the subjective and objective refractions of the object appear4 #cah4 ,if we look through a prism1 held with its refracting angle underneath1 at an object above us1 the object is moved downwards2 whereas a luminous image refracted through the same prism is moved upwards4 ,this1 which we here merely mention as a matter of fact for the sake of brevity1 is easily explained by the laws of refraction and elevation4 #cai4 ,the luminous object being moved from its place in this manner1 the coloured borders appear in the order1 and according to the laws before explained4 ,the violet border is always foremost1 and thus in objective cases proceeds upwards1 in subjective cases downwards4 #cbj 7#bje74 ,the observer may convince himself in like manner of the mode in which the appearance of colour takes place in the diagonal direction when the displacement is effected by means of two prisms1 as has been plainly enough shown in the subjective example2 for this experiment1 however1 prisms should be procured of few degrees1 say about fifteen4 #cba7bjf1 #bjg74 ,that the colouring of the image takes place here too1 according to the direction in which it moves1 will be apparent if we make a square opening of moderate size in a shutter1 and cause the luminous image to pass through a water-prism2 the spectrum being moved first in the horizontal and vertical directions1 then diagonally1 the coloured edges will change their position accordingly4 #cbb7bjh74 ,whence it is again evident that to produce colour the boundaries must be carried over each other1 not merely move side by side4 ,,xxiii4 ,,conditions ,,of ,,the ,,increase ,,of ,,colour4 #cbc 7#bji74 ,here too an increased displacement of the object produces a greater appearance of colour4 #cbd 7#baj74 ,this increased displacement occurs1 #a4 ,by a more oblique direction of the impinging luminous object through mediums with parallel surfaces4 #b4 ,by changing the parallel form for one more or less acute angled4 #c4 ,by increased proportion of the medium1 whether parallel or acute angled2 partly because the object is by this means more powerfully displaced1 partly because an effect depending on the mere mass co-operates4 #d4 ,by the distance of the recipient surface from the refracting medium so that the coloured spectrum emerging from the prism may be said to have a longer way to travel4 #e4 ,when a chemical property produces its effects under all these circumstances3 this we have already entered into more fully under the head of achromatism and hyperchromatism4 #cbe 7#baa74 ,the objective experiments have this advantage that the progressive states of the phenomenon may be arrested and clearly represented by diagrams1 which is not the case with the subjective experiments4 #cbf4 ,we can observe the luminous image after it has emerged from the prism1 step by step1 and mark its increasing colour by receiving it on a plane at different distances1 thus exhibiting before our eyes various sections of this cone1 with an elliptical base3 again1 the phenomenon may at once be rendered beautifully visible throughout its whole course in the following manner3--,let a cloud of fine white dust be excited along the line in which the image passes through the dark space2 the cloud is best produced by fine1 perfectly dry1 hair-powder4 ,the more or less coloured appearance will now be painted on the white atoms1 and presented in its whole length and breadth to the eye of the spectator4 #cbg4 ,by this means we have prepared some diagrams1 which will be found among the plates4 ,in these the appearance is exhibited from its first origin1 and by these the spectator can clearly comprehend why the luminous image is so much more powerfully coloured through prisms than through parallel mediums4 #cbh 7#bab74 ,at the two opposite outlines of the image an opposite appearance presents itself1 beginning from an acute angle2#a the appearance spreads as it proceeds further in space1 according to this angle4 ,on one side1 in the direction in which the luminous image is moved1 a violet border advances on the dark1 a narrower blue edge remains next the outline of the image4 ,on the opposite side a yellow border advances into the light of the image itself1 and a yellow-red edge remains at the outline4 #cbi 7#bac74 ,here1 therefore1 the movement of the dark against the light1 of the light against the dark1 may be clearly observed4 ,illustration #ccj 7#bad74 ,the centre of a large object remains long uncoloured1 especially with mediums of less density and smaller angles2 but at last the opposite borders and edges touch each other1 upon which a green appears in the centre of the luminous image4 #cca 7#bae74 ,objective experiments have been usually made with the sun's image3 an objective experiment with a dark object has hitherto scarcely been thought of4 ,we have1 however1 prepared a convenient contrivance for this also4 ,let the large water-prism before alluded to be placed in the sun1 and let a round pasteboard disk be fastened either inside or outside4 ,the coloured appearance will again take place at the outline1 beginning according to the usual law2 the edges will appear1 they will spread in the same proportion1 and when they meet1 red will appear in the centre#b4 ,an intercepting square may be added near the round disk1 and placed in any direction ad libitum1 and the spectator can again convince himself of what has been before so often described4 #ccb 7#baf74 ,if we take away these dark objects from the prism1 in which case1 however1 the glass is to be carefully cleaned1 and hold a rod or a large pencil before the centre of the horizontal prism1 we shall then accomplish the complete immixture of the violet border and the yellow-red edge1 and see only the three colours1 the external blue1 and yellow1 and the central red4 #ccc4 ,if again we cut a long horizontal opening in the middle of a piece of pasteboard1 fastened on the prism1 and then cause the sun-light to pass through it1 we shall accomplish the complete union of the yellow border with the blue edge upon the light1 and only see yellow-red1 green and violet4 ,the details of this are further entered into in the description of the plates4 #ccd 7#bag74 ,the prismatic appearance is thus by no means complete and final when the luminous image emerges from the prism4 ,it is then only that we perceive its elements in contrast2 for as it increases these contrasting elements unite1 and are at last intimately joined4 ,the section of this phenomenon arrested on a plane surface is different at every degree of distance from the prism2 so that the notion of an immutable series of colours1 or of a pervading similar proportion between them1 cannot be a question for a moment4 #a ,plate #d4 fig4 #a4 #b ,plate #d4 fig4 #b4 ,,xxiv4 ,,explanation ,,of ,,the ,,foregoing ,,phenomena4 #cce 7#bah74 ,as we have already entered into this analysis circumstantially while treating of the subjective experiments1 as all that was of force there is equally valid here1 it will require no long details in addition to show that the phenomena1 which are entirely parallel in the two cases1 may also be traced precisely to the same sources4 #ccf 7#bai74 ,that in objective experiments also we have to do with circumscribed images1 has been already demonstrated at large4 ,the sun may shine through the smallest opening1 yet the image of the whole disk penetrates beyond4 ,the largest prism may be placed in the open sun-light1 yet it is still the sun's image that is bounded by the edges of the refracting surfaces1 and produces the accessory images of this boundary4 ,we may fasten pasteboard1 with many openings cut in it1 before the water-prism1 yet we still merely see multiplied images which1 after having been moved from their place by refraction1 exhibit coloured edges and borders1 and in these mere accessory images4 #ccg 7#bce74 ,in subjective experiments we have seen that objects strongly relieved from each other produce a very lively appearance of colour1 and this will be the case in objective experiments in a much more vivid and splendid degree4 ,the sun's image is the most powerful brightness we know2 hence its accessory image will be energetic in proportion1 and notwithstanding its really secondary dimmed and darkened character1 must be still very brilliant4 ,the colours thrown by the sun-light through the prism on any object1 carry a powerful light with them1 for they have the highest and most intense source of light1 as it were1 for their ground4 #cch4 ,that we are warranted in calling even these accessory images semi-transparent1 thus deducing the appearances from the doctrine of the semi-transparent mediums1 will be clear to every one who has followed us thus far1 but particularly to those who have supplied themselves with the necessary apparatus1 so as to be enabled at all times to witness the precision and vivacity with which semi-transparent mediums act4 ,,xxv4 ,,decrease ,,of ,,the ,,appearance ,,of ,,colour4 #cci 7#bdc74 ,if we could afford to be concise in the description of the decreasing coloured appearance in subjective cases1 we may here be permitted to proceed with still greater brevity while we refer to the former distinct statement4 ,one circumstance1 only on account of its great importance1 may be here recommended to the reader's especial attention as a leading point of our whole thesis4 #cdj 7#bdd1 #bdg74 ,the decline of the prismatic appearance must be preceded by its separation1 by its resolution into its elements4 ,at a due distance from the prism1 the image of the sun being entirely coloured1 the blue and yellow at length mix completely1 and we see only yellow-red1 green1 and blue-red4 ,if we bring the recipient surface nearer to the refracting medium1 yellow and blue appear again1 and we see the five colours with their gradations4 ,at a still shorter distance the yellow and blue separate from each other entirely1 the green vanishes1 and the image itself appears1 colourless1 between the coloured edges and borders4 ,the nearer we bring the recipient surface to the prism1 the narrower the edges and borders become1 till at last1 when in contact with the prism1 they are reduced to nothing4 ,,xxvi4 ,,grey ,,objects4 #cda 7#bah74 ,we have exhibited grey objects as very important to our inquiry in the subjective experiments4 ,they show1 by the faintness of the accessory images1 that these same images are in all cases derived from the principal object4 ,if we wish here1 too1 to carry on the objective experiments parallel with the others1 we may conveniently do this by placing a more or less dull ground glass before the opening through which the sun's image enters4 ,by this means a subdued image would be produced1 which on being refracted would exhibit much duller colours on the recipient plane than those immediately derived from the sun's disk2 and thus1 even from the intense sun-image1 only a faint accessory image would appear1 proportioned to the mitigation of the light by the glass4 ,this experiment1 it is true1 will only again and again confirm what is already sufficiently familiar to us4 ,,xxvii4 ,,coloured ,,objects4 #cdb 7#bfj74 ,there are various modes of producing coloured images in objective experiments4 ,in the first place1 we can fix coloured glass before the opening1 by which means a coloured image is at once produced2 secondly1 we can fill the water-prism with coloured fluids2 thirdly1 we can cause the colours1 already produced in their full vivacity by the prism1 to pass through proportionate small openings in a tin plate1 and thus prepare small circumscribed colours for a second operation4 ,this last mode is the most difficult2 for owing to the continual progress of the sun1 the image cannot be arrested in any direction at will4 ,the second method has also its inconveniences1 since not all coloured liquids can be prepared perfectly bright and clear4 ,on these accounts the first is to be preferred1 and deserves the more to be adopted because natural philosophers have hitherto chosen to consider the colours produced from the sun-light through the prism1 those produced through liquids and glasses1 and those which are already fixed on paper or cloth1 as exhibiting effects equally to be depended on1 and equally available in demonstration4 #cdc4 ,as it is thus merely necessary that the image should be coloured1 so the large water-prism before alluded to affords us the best means of effecting this4 ,a pasteboard screen may be contrived to slide before the large surfaces of the prism1 through which1 in the first instance1 the light passes uncoloured4 ,in this screen openings of various forms may be cut1 in order to produce different images1 and consequently different accessory images4 ,this being done1 we need only fix coloured glasses before the openings1 in order to observe what effect refraction produces on coloured images in an objective sense4 #cdd4 ,a series of glasses may be prepared in a mode similar to that before described 7#bhd72 these should be accurately contrived to slide in the grooves of the large water-prism4 ,let the sun then shine through them1 and the coloured images refracted upwards will appear bordered and edged1 and will vary accordingly3 for these borders and edges will be exhibited quite distinctly on some images1 and on others will be mixed with the specific colour of the glass1 which they will either enhance or neutralize4 ,every observer will be enabled to convince himself here again that we have only to do with the same simple phenomenon so circumstantially described subjectively and objectively4 ,,xxviii4 ,,achromatism ,,and ,,hyperchromatism4 #cde 7#bhe1 #bij74 ,it is possible to make the hyperchromatic and achromatic experiments objectively as well as subjectively4 ,after what has been already stated1 a short description of the method will suffice1 especially as we take it for granted that the compound prism before mentioned is in the hands of the observer4 #cdf4 ,let the sun's image pass through an acute-angled prism of few degrees1 prepared from crown-glass1 so that the spectrum be refracted upwards on an opposite surface2 the edges will appear coloured1 according to the constant law1 namely1 the violet and blue above and outside1 the yellow and yellow-red below and within the image4 ,as the refracting angle of this prism is undermost1 let another proportionate prism of flint-glass be placed against it1 with its refracting angle uppermost4 ,the sun's image will by this means be again moved to its place1 where1 owing to the excess of the colouring power of the prism of flint-glass1 it will still appear a little coloured1 and1 in consequence of the direction in which it has been moved1 the blue and violet will now appear underneath and outside1 the yellow and yellow-red above and inside4 #cdg4 ,if the whole image be now moved a little upwards by a proportionate prism of crown-glass1 the hyperchromatism will disappear1 the sun's image will be moved from its place1 and yet will appear colourless4 #cdh4 ,with an achromatic object-glass composed of three glasses1 this experiment may be made step by step1 if we do not mind taking out the glasses from their setting4 ,the two convex glasses of crown-glass in contracting the sun's image towards the focus1 the concave glass of flint-glass in dilating the image beyond it1 exhibit at the edges the usual colours4 ,a convex glass united with a concave one exhibits the colours according to the law of the latter4 ,if all three glasses are placed together1 whether we contract the sun's image towards the focus1 or suffer it to dilate beyond the focus1 coloured edges never appear1 and the achromatic effect intended by the optician is1 in this case1 again attained4 #cdi4 ,but as the crown-glass has always a greenish tint1 and as a tendency to this hue may be more decided in large and strong object-glasses1 and under certain circumstances produce the compensatory red1 7which1 however1 in repeated experiments with several instruments of this kind did not occur to us17 philosophers have resorted to the most extraordinary modes of explaining such a result2 and having been compelled1 in support of their system1 theoretically to prove the impossibility of achromatic telescopes1 have felt a kind of satisfaction in having some apparent ground for denying so great an improvement4 ,of this1 however1 we can only treat circumstantially in our historical account of these discoveries4 ,,xxix4 ,,combination ,,of ,,subjective ,,and ,,objective ,,experiments4 #cej4 ,having shown above 7#cah7 that refraction1 considered objectively and subjectively1 must act in opposite directions1 it will follow that if we combine the experiments1 the effects will reciprocally destroy each other4 #cea4 ,let the sun's image be thrown upwards on a vertical plane1 through a horizontally-placed prism4 ,if the prism is long enough to admit of the spectator also looking through it1 he will see the image elevated by the objective refraction again depressed1 and in the same place in which it appeared without refraction4 #ceb4 ,here a remarkable case presents itself1 but at the same time a natural result of a general law4 ,for since1 as often before stated1 the objective sun's image thrown on the vertical plane is not an ultimate or unchangeable state of the phenomenon1 so in the above operation the image is not only depressed when seen through the prism1 but its edges and borders are entirely robbed of their hues1 and the spectrum is reduced to a colourless circular form4 #cec4 ,by employing two perfectly similar prisms placed next each other1 for this experiment1 we can transmit the sun's image through one1 and look through the other4 #ced4 ,if the spectator advances nearer with the prism through which he looks1 the image is again elevated1 and by degrees becomes coloured according to the law of the first prism4 ,if he again retires till he has brought the image to the neutralized point1 and then retires still farther away1 the image1 which had become round and colourless1 moves still more downwards and becomes coloured in the opposite sense1 so that if we look through the prism and upon the refracted spectrum at the same time1 we see the same image coloured according to subjective and objective laws4 #cee4 ,the modes in which this experiment may be varied are obvious4 ,if the refracting angle of the prism1 through which the sun's image was objectively elevated1 is greater than that of the prism through which the observer looks1 he must retire to a much greater distance1 in order to depress the coloured image so low on the vertical plane that it shall appear colourless1 and vice vers4 #cef4 ,it will be easily seen that we may exhibit achromatic and hyperchromatic effects in a similar manner1 and we leave it to the amateur to follow out such researches more fully4 ,other complicated experiments in which prisms and lenses are employed together1 others again1 in which objective and subjective experiments are variously intermixed1 we reserve for a future occasion1 when it will be our object to trace such effects to the simple phenomena with which we are now sufficiently familiar4 ,,xxx4 ,,transition4 #ceg4 ,in looking back on the description and analysis of dioptrical colours1 we do not repent either that we have treated them so circumstantially1 or that we have taken them into consideration before the other physical colours1 out of the order we ourselves laid down4 ,yet1 before we quit this branch of our inquiry1 it may be as well to state the reasons that have weighed with us4 #ceh4 ,if some apology is necessary for having treated the theory of the dioptrical colours1 particularly those of the second class1 so diffusely1 we should observe1 that the exposition of any branch of knowledge is to be considered partly with reference to the intrinsic importance of the subject1 and partly with reference to the particular necessities of the time in which the inquiry is undertaken4 ,in our own case we were forced to keep both these considerations constantly in view4 ,in the first place we had to state a mass of experiments with our consequent convictions2 next1 it was our especial aim to exhibit certain phenomena 7known1 it is true1 but misunderstood1 and above all1 exhibited in false connection17 in that natural and progressive development which is strictly and truly conformable to observation2 in order that hereafter1 in our polemical or historical investigations1 we might be enabled to bring a complete preparatory analysis to bear on1 and elucidate1 our general view4 ,the details we have entered into were on this account unavoidable2 they may be considered as a reluctant consequence of the occasion4 ,hereafter1 when philosophers will look upon a simple principle as simple1 a combined effect as combined2 when they will acknowledge the first elementary1 and the second complicated states1 for what they are2 then1 indeed1 all this statement may be abridged to a narrower form2 a labour which1 should we ourselves not be able to accomplish it1 we bequeath to the active interest of contemporaries and posterity4 #cei4 ,with respect to the order of the chapters1 it should be remembered that natural phenomena1 which are even allied to each other1 are not connected in any particular sequence or constant series2 their efficient causes act in a narrow circle1 so that it is in some sort indifferent what phenomenon is first or last considered2 the main point is1 that all should be as far as possible present to us1 in order that we may embrace them at last from one point of view1 partly according to their nature1 partly according to generally received methods4 #cfj4 ,yet1 in the present particular instance1 it may be asserted that the dioptrical colours are justly placed at the head of the physical colours2 not only on account of their striking splendour and their importance in other respects1 but because1 in tracing these to their source1 much was necessarily entered into which will assist our subsequent enquiries4 #cfa4 ,for1 hitherto1 light has been considered as a kind of abstract principle1 existing and acting independently2 to a certain extent self-modified1 and on the slightest cause1 producing colours out of itself4 ,to divert the votaries of physical science from this mode of viewing the subject2 to make them attentive to the fact1 that in prismatic and other appearances we have not to do with light as an uncircumscribed and modifying principle1 but as circumscribed and modified2 that we have to do with a luminous image2 with images or circumscribed objects generally1 whether light or dark3 this was the purpose we had in view1 and such is the problem to be solved4 #cfb4 ,all that takes place in dioptrical cases1--especially those of the second class which are connected with the phenomena of refraction1--is now sufficiently familiar to us1 and will serve as an introduction to what follows4 #cfc4 ,catoptrical appearances remind us of the physiological phenomena1 but as we ascribe a more objective character to the former1 we thought ourselves justified in classing them with the physical examples4 ,it is of importance1 however1 to remember that here again it is not light1 in an abstract sense1 but a luminous image that we have to consider4 #cfd4 ,in proceeding onwards to the paroptrical class1 the reader1 if duly acquainted with the foregoing facts1 will be pleased to find himself once more in the region of circumscribed forms4 ,the shadows of bodies1 especially1 as secondary images1 so exactly accompanying the object1 will serve greatly to elucidate analogous appearances4 #cfe4 ,we will not1 however1 anticipate these statements1 but proceed as heretofore in what we consider the regular course4 ,,xxxi4 ,,catoptrical ,,colours4 #cff4 ,catoptrical colours are such as appear in consequence of a mirror-like reflection4 ,we assume1 in the first place1 that the light itself as well as the surface from which it is reflected1 is perfectly colourless4 ,in this sense the appearances in question come under the head of physical colours4 ,they arise in consequence of reflection1 as we found the dioptrical colours of the second class appear by means of refraction4 ,without further general definitions1 we turn our attention at once to particular cases1 and to the conditions which are essential to the exhibition of these phenomena4 #cfg4 ,if we unroll a coil of bright steel-wire1 and after suffering it to spring confusedly together again1 place it at a window in the light1 we shall see the prominent parts of the circles and convolutions illumined1 but neither resplendent nor iridescent4 ,but if the sun shines on the wire1 this light will be condensed into a point1 and we perceive a small resplendent image of the sun1 which1 when seen near1 exhibits no colour4 ,on retiring a little1 however1 and fixing the eyes on this refulgent appearance1 we discern several small mirrored suns1 coloured in the most varied manner2 and although the impression is that green and red predominate1 yet1 on a more accurate inspection1 we find that the other colours are also present4 #cfh4 ,if we take an eye-glass1 and examine the appearance through it1 we find the colours have vanished1 as well as the radiating splendour in which they were seen1 and we perceive only the small luminous points1 the repeated images of the sun4 ,we thus find that the impression is subjective in its nature1 and that the appearance is allied to those which we have adverted to under the name of radiating halos 7#ajj74 #cfi4 ,we can1 however1 exhibit this phenomenon objectively4 ,let a piece of white paper be fastened beneath a small aperture in the lid of a camera-obscura1 and when the sun shines through this aperture1 let the confusedly-rolled steel-wire be held in the light1 so that it be opposite to the paper4 ,the sun-light will impinge on and in the circles of the wire1 and will not1 as in the concentrating lens of the eye1 display itself in a point2 but1 as the paper can receive the reflection of the light in every part of its surface will be seen in hair-like lines1 which are also iridescent4 #cgj4 ,this experiment is purely catoptrical2 for as we cannot imagine that the light penetrates the surface of the steel1 and thus undergoes a change1 we are soon convinced that we have here a mere reflection which1 in its subjective character1 is connected with the theory of faintly acting lights1 and the after-image of dazzling lights1 and as far as it can be considered objective1 announces even in the minutest appearances1 a real effect1 independent of the action and reaction of the eye4 #cga4 ,we have seen that to produce these effects not merely light but a powerful light is necessary2 that this powerful light again is not an abstract and general quality1 but a circumscribed light1 a luminous image4 ,we can convince ourselves still further of this by analogous cases4 #cgb4 ,a polished surface of silver placed in the sun reflects a dazzling light1 but in this case no colour is seen4 ,if1 however1 we slightly scratch the surface1 an iridescent appearance1 in which green and red are conspicuous1 will be exhibited at a certain angle4 ,in chased and carved metals the effect is striking3 yet it may be remarked throughout that1 in order to its appearance1 some form1 some alternation of light and dark must co-operate with the reflection2 thus a window-bar1 the stem of a tree1 an accidentally or purposely interposed object produces a perceptible effect4 ,this appearance1 too1 may be exhibited objectively in the camera-obscura4 #cgc4 ,if we cause a polished plated surface to be so acted on by aqua fortis that the copper within is touched1 and the surface itself thus rendered rough1 and if the sun's image be then reflected from it1 the splendour will be reverberated from every minutest prominence1 and the surface will appear iridescent4 ,so1 if we hold a sheet of black unglazed paper in the sun1 and look at it attentively1 it will be seen to glisten in its minutest points with the most vivid colours4 #cgd4 ,all these examples are referable to the same conditions4 ,in the first case the luminous image is reflected from a thin line2 in the second probably from sharp edges2 in the third from very small points4 ,in all a very powerful and circumscribed light is requisite4 ,for all these appearances of colour again it is necessary that the eye should be at a due distance from the reflecting points4 #cge4 ,if these observations are made with the microscope1 the appearance will be greatly increased in force and splendour1 for we then see the smallest portion of the surfaces1 lit by the sun1 glittering in these colours of reflection1 which1 allied to the hues of refraction1 now attain their highest degree of brilliancy4 ,in such cases we may observe a vermiform iridescence on the surface of organic bodies1 the further description of which will be given hereafter4 #cgf4 ,lastly1 the colours which are chiefly exhibited in reflection are red and green1 whence we may infer that the linear appearance especially consists of a thin line of red1 bounded by blue on one side and yellow on the other4 ,if these triple lines approach very near together1 the intermediate space must appear green2 a phenomenon which will often occur to us as we proceed4 #cgg4 ,we frequently meet with these colours in nature4 ,the colours of the spider's web might be considered exactly of the same class with those reflected from the steel wire1 except that the non-translucent quality of the former is not so certain as in the case of steel2 on which account some have been inclined to class the colours of the spider's web with the phenomena of refraction4 #cgh4 ,in mother-of-pearl we perceive infinitely fine organic fibres and lamell in juxta-position1 from which1 as from the scratched silver before alluded to1 varied colours1 but especially red and green1 may arise4 #cgi4 ,the changing colours of the plumage of birds may also be mentioned here1 although in all organic instances a chemical principle and an adaptation of the colour to the structure may be assumed2 considerations to which we shall return in treating of chemical colours4 #chj4 ,that the appearances of objective halos also approximate catoptrical phenomena will be readily admitted1 while we again do not deny that refraction as well may here come into the account4 ,for the present we restrict ourselves to one or two observations2 hereafter we may be enabled to make a fuller application of general principles to particular examples4 #cha4 ,we first call to mind the yellow and red circles produced on a white or grey wall by a light placed near it 7#hh74 ,light when reflected appears subdued1 and a subdued light excites the impression of yellow1 and subsequently of red4 #chb4 ,let the wall be illumined by a candle placed quite close to it4 ,the farther the light is diffused the fainter it becomes2 but it is still the effect of the flame1 the continuation of its action1 the dilated effect of its image4 ,we might1 therefore1 very fairly call these circles reiterated images1 because they constitute the successive boundaries of the action of the light1 and yet at the same time only present an extended image of the flame4 #chc4 ,if the sky is white and luminous round the sun owing to the atmosphere being filled with light vapours2 if mists or clouds pass before the moon1 the reflection of the disk mirrors itself in them2 the halos we then perceive are single or double1 smaller or greater1 sometimes very large1 often colourless1 sometimes coloured4 #chd4 ,i witnessed a very beautiful halo round the moon the #aeth of ,november1 #agii1 when the barometer stood high2 the sky was cloudy and vapoury4 ,the halo was completely coloured1 and the circles were concentric round the light as in subjective halos4 ,that this halo was objective ,i was presently convinced by covering the moon's disk1 when the same circles were nevertheless perfectly visible4 #che4 ,the different extent of the halos appears to have a relation with the proximity or distance of the vapour from the eye of the observer4 #chf4 ,as window-panes lightly breathed upon increase the brilliancy of subjective halos1 and in some degree give them an objective character1 so1 perhaps1 with a simple contrivance in winter1 during a quickly freezing temperature1 a more exact definition of this might be arrived at4 #chg4 ,how much reason we have in considering these circles to insist on the image and its effects1 is apparent in the phenomenon of the so-called double suns4 ,similar double images always occur in certain points of halos and circles1 and only present in a circumscribed form what takes place in a more general way in the whole circle4 ,all this will be more conveniently treated in connexion with the appearance of the rainbow4--,note ,q4 #chh4 ,in conclusion it is only necessary to point out the affinity between the catoptrical and paroptical colours4 ,we call those paroptical colours which appear when the light passes by the edge of an opaque colourless body4 ,how nearly these are allied to the dioptrical colours of the second class will be easily seen by those who are convinced with us that the colours of refraction ,pg #afc take place only at the edges of objects4 ,the affinity again between the catoptrical and paroptical colours will be evident in the following chapter4 ,,xxxii4 ,,paroptical ,,colours4 #chi4 ,the paroptical colours have been hitherto called peri-optical1 because a peculiar effect of light was supposed to take place as it were round the object1 and was ascribed to a certain flexibility of the light to and from the object4 #cij4 ,these colours again may be divided into subjective and objective1 because they appear partly without us1 as it were1 painted on surfaces1 and partly within us1 immediately on the retina4 ,in this chapter we shall find it more to our purpose to take the objective cases first1 since the subjective are so closely connected with other appearances already known to us1 that it is hardly possible to separate them4 #cia4 ,the paroptical colours then are so called because the light must pass by an outline or edge to produce them4 ,they do not1 however1 always appear in this case2 to produce the effect very particular conditions are necessary besides4 #cib4 ,it is also to be observed that in this instance again light does not act as an abstract diffusion 7#cfa71 the sun shines towards an edge4 ,the volume of light poured from the sun-image passes by the edge of a substance1 and occasions shadows4 ,within these shadows we shall presently find colours appear4 #cic4 ,but1 above all1 we should make the experiments and observations that bear upon our present inquiry in the fullest light4 ,we1 therefore1 place the observer in the open air before we conduct him to the limits of a dark room4 #cid4 ,a person walking in sun-shine in a garden1 or on any level path1 may observe that his shadow only appears sharply defined next the foot on which he rests2 farther from this point1 especially round the head1 it melts away into the bright ground4 ,for as the sun-light proceeds not only from the middle of the sun1 but also acts cross-wise from the two extremes of every diameter1 an objective parallax takes place which produces a half-shadow on both sides of the object4 #cie4 ,if the person walking raises and spreads his hand1 he distinctly sees in the shadow of each finger the diverging separation of the two half-shadows outwards1 and the diminution of the principal shadow inwards1 both being effects of the cross action of the light4 #cif4 ,this experiment may be repeated and varied before a smooth wall1 with rods of different thicknesses1 and again with balls2 we shall always find that the farther the object is removed from the surface of the wall1 the more the weak double shadow spreads1 and the more the forcible main shadow diminishes1 till at last the main shadow appears quite effaced1 and even the double shadows become so faint1 that they almost disappear2 at a still greater distance they are1 in fact1 imperceptible4 #cig4 ,that this is caused by the cross-action of the light we may easily convince ourselves2 for the shadow of a pointed object plainly exhibits two points4 ,we must thus never lose sight of the fact that in this case the whole sun-image acts1 produces shadows1 changes them to double shadows1 and finally obliterates them4 #cih4 ,instead of solid bodies let us now take openings cut of various given sizes next each other1 and let the sun shine through them on a plane surface at some little distance2 we shall find that the bright image produced by the sun on the surface1 is larger than the opening2 this is because one edge of the sun shines towards the opposite edge of the opening1 while the other edge of the disk is excluded on that side4 ,hence the bright image is more weakly lighted towards the edges4 #cii4 ,if we take square openings of any size we please1 we shall find that the bright image on a surface nine feet from the opening1 is on every side about an inch larger than the opening2 thus nearly corresponding with the angle of the apparent diameter of the sun4 #djj4 ,that the brightness should gradually diminish towards the edges of the image is quite natural1 for at last only a minimum of the light can act cross-wise from the sun's circumference through the edge of the aperture4 #dja4 ,thus we here again see how much reason we have in actual observation to guard against the assumption of parallel rays1 bundles and fasces of rays1 and the like hypothetical notions4 #djb4 ,we might rather consider the splendour of the sun1 or of any light1 as an infinite specular multiplication of the circumscribed luminous image1 whence it may be explained that all square openings through which the sun shines1 at certain distances1 according as the apertures are greater or smaller1 must give a round image of light4 #djc4 ,the above experiments may be repeated through openings of various shapes and sizes1 and the same effect will always take place at proportionate distances4 ,in all these cases1 however1 we may still observe that in a full light and while the sun merely shines past an edge1 no colour is apparent4 #djd4 ,we therefore proceed to experiments with a subdued light1 which is essential to the appearance of colour4 ,let a small opening be made in the window-shutter of a dark room2 let the crossing sun-light which enters1 be received on a surface of white paper1 and we shall find that the smaller the opening is1 the dimmer the light image will be4 ,this is quite obvious1 because the paper does not receive light from the whole sun1 but partially from single points of its disk4 #dje4 ,if we look attentively at this dim image of the sun1 we find it still dimmer towards the outlines where a yellow border is perceptible4 ,the colour is still more apparent if a vapour or a transparent cloud passes before the sun1 thus subduing and dimming its brightness4 ,the halo on the wall1 the effect of the decreasing brightness of a light placed near it1 is here forced on our recollection4 7#hh47 #djf4 ,if we examine the image more accurately1 we perceive that this yellow border is not the only appearance of colour2 we can see1 besides1 a bluish circle1 if not even a halo-like repetition of the coloured border4 ,if the room is quite dark1 we discern that the sky next the sun also has its effect3 we see the blue sky1 nay1 even the whole landscape1 on the paper1 and are thus again convinced that as far as regards the sun1 we have here only to do with a luminous image4 #djg4 ,if we take a somewhat larger square opening1 so large that the image of the sun shining through it does not immediately become round1 we may distinctly observe the half-shadows of every edge or side1 the junction of these in the corners1 and their colours2 just as in the above-mentioned appearance with the round opening4 #djh4 ,we have now subdued a parallactic light by causing it to shine through small apertures1 but we have not taken from it its parallactic character2 so that it can produce double shadows of bodies1 although with diminished power4 ,these double shadows which we have hitherto been describing1 follow each other in light and dark1 coloured and colourless circles1 and produce repeated1 nay1 almost innumerable halos4 ,these effects have been often represented in drawings and engravings4 ,by placing needles1 hairs1 and other small bodies1 in the subdued light1 the numerous halo-like double shadows may be increased2 thus observed1 they have been ascribed to an alternating flexile action of the light1 and the same assumption has been employed to explain the obliteration of the central shadow1 and the appearance of a light in the place of the dark4 #dji4 ,for ourselves1 we maintain that these again are parallactic double shadows1 which appear edged with coloured borders and halos4 #daj4 ,after having seen and investigated the foregoing phenomena1 we can proceed to the experiments with knife-blades1#a exhibiting effects which may be referred to the contact and parallactic mutual intersection of the half-shadows and halos already familiar to us4 #daa4 ,lastly1 the observer may follow out the experiments with hairs1 needles1 and wires1 in the half-light produced as before described by the sun1 as well as in that derived from the blue sky1 and indicated on the white paper4 ,he will thus make himself still better acquainted with the true nature of this phenomenon4 #dab4 ,but since in these experiments everything depends on our being persuaded of the parallactic action of the light1 we can make this more evident by means of two sources of light1 the two shadows from which intersect each other1 and may be altogether separated4 ,by day this may be contrived with two small openings in a window-shutter2 by night1 with two candles4 ,there are even accidental effects in interiors1 on opening and closing shutters1 by means of which we can better observe these appearances than with the most careful apparatus4 ,but still1 all and each of these may be reduced to experiment by preparing a box which the observer can look into from above1 and gradually diminishing the openings after having caused a double light to shine in4 ,in this case1 as might be expected1 the coloured shadow1 considered under the physiological colours1 appears very easily4 #dac4 ,it is necessary to remember1 generally1 what has been before stated with regard to the nature of double shadows1 half-lights1 and the like4 ,experiments also should especially be made with different shades of grey placed next each other1 where every stripe will appear light by a darker1 and dark by a lighter stripe next it4 ,if at night1 with three or more lights1 we produce shadows which cross each other successively1 we can observe this phenomenon very distinctly1 and we shall be convinced that the physiological case before more fully treated1 here comes into the account 7#ch74 #dad4 ,to what extent the appearances that accompany the paroptical colours1 may be derived from the doctrine of subdued lights1 from half-shadows1 and from the physiological disposition of the retina1 or whether we shall be forced to take refuge in certain intrinsic qualities of light1 as has hitherto been done1 time may teach4 ,suffice it here to have pointed out the conditions under which the paroptical colours appear1 and we may hope that our allusion to their connexion with the facts before adduced by us will not remain unnoticed by the observers of nature4 #dae4 ,the affinity of the paroptical colours with the dioptrical of the second class will also be readily seen and followed up by every reflecting investigator4 ,here1 as in those instances1 we have to do with edges or boundaries2 here1 as in those instances1 with a light1 which appears at the outline4 ,how natural1 therefore1 it is to conclude that the paroptical effects may be heightened1 strengthened1 and enriched by the dioptrical4 ,since1 however1 the luminous image actually shines through the medium1 we can here only have to do with objective cases of refraction3 it is these which are strictly allied to the paroptical cases4 ,the subjective cases of refraction1 where we see objects through the medium1 are quite distinct from the paroptical4 ,we have already recommended them on account of their clearness and simplicity4 #daf4 ,the connexion between the paroptical colours and the catoptrical may be already inferred from what has been said3 for as the catoptrical colours only appear on scratches1 points1 steel-wire1 and delicate threads1 so it is nearly the same case as if the light shone past an edge4 ,the light must always be reflected from an edge in order to produce colour4 ,here again1 as before pointed out1 the partial action of the luminous image and the subduing of the light are both to be taken into the account4 #dag4 ,we add but few observations on the subjective paroptical colours1 because these may be classed partly with the physiological colours1 partly with the dioptrical of the second order4 ,the greater part hardly seem to belong here1 but1 when attentively considered1 they still diffuse a satisfactory light over the whole doctrine1 and establish its connexion4 #dah4 ,if we hold a ruler before the eyes so that the flame of a light just appears above it1 we see the ruler as it were indented and notched at the place where the light appears4 ,this seems deducible from the expansive power of light acting on the retina 7#ah74 #dai4 ,the same phenomenon on a large scale is exhibited at sun-rise2 for when the orb appears distinctly1 but not too powerfully1 so that we can still look at it1 it always makes a sharp indentation in the horizon4 #dbj4 ,if1 when the sky is grey1 we approach a window1 so that the dark cross of the window-bars be relieved on the sky2 if after fixing the eyes on the horizontal bar we bend the head a little forward2 on half closing the eyes as we look up1 we shall presently perceive a bright yellow-red border under the bar1 and a bright light-blue one above it4 ,the duller and more monotonous the grey of the sky1 the more dusky the room1 and1 consequently1 the more previously unexcited the eye1 the livelier the appearance will be2 but it may be seen by an attentive observer even in bright daylight4 #dba4 ,if we move the head backwards while half closing the eyes1 so that the horizontal bar be seen below1 the phenomenon will appear reversed4 ,the upper edge will appear yellow1 the under edge blue4 #dbb4 ,such observations are best made in a dark room4 ,if white paper is spread before the opening where the solar microscope is commonly fastened1 the lower edge of the circle will appear blue1 the upper yellow1 even while the eyes are quite open1 or only by half-closing them so far that a halo no longer appears round the white4 ,if the head is moved backwards the colours are reversed4 #dbc4 ,these phenomena seem to prove that the humours of the eye are in fact only really achromatic in the centre where vision takes place1 but that towards the circumference1 and in unusual motions of the eyes1 as in looking horizontally when the head is bent backwards or forwards1 a chromatic tendency remains1 especially when distinctly relieved objects are thus looked at4 ,hence such phenomena may be considered as allied to the dioptrical colours of the second class4 #dbd4 ,similar colours appear if we look on black and white objects1 through a pin-hole in a card4 ,instead of a white object we may take the minute light aperture in the tin plate of a camera obscura1 as prepared for paroptical experiments4 #dbe4 ,if we look through a tube1 the farther end of which is contracted or variously indented1 the same colours appear4 #dbf4 ,the following phenomena appear to me to be more nearly allied to the paroptical appearances4 ,if we hold up a needle near the eye1 the point appears double4 ,a particularly remarkable effect again is produced if we look towards a grey sky through the blades of knives prepared for paroptical experiments4 ,we seem to look through a gauze2 a multitude of threads appear to the eye2 these are in fact only the reiterated images of the sharp edges1 each of which is successively modified by the next1 or perhaps modified in a parallactic sense by the oppositely acting one1 the whole mass being thus changed to a thread-like appearance4 #dbg4 ,lastly1 it is to be remarked that if we look through the blades towards a minute light in the window-shutter1 coloured stripes and halos appear on the retina as on the paper4 #dbh4 ,the present chapter may be here terminated1 the less reluctantly1 as a friend has undertaken to investigate this subject by further experiments4 ,in our recapitulation1 in the description of the plates and apparatus1 we hope hereafter to give an account of his observations4#b #a ,see ,newton's ,optics1 book iii4 #b ,the observations here alluded to never appeared4 ,,xxxiii4 ,,epoptical ,,colours4 #dbi4 ,we have hitherto had to do with colours which appear with vivacity1 but which immediately vanish again when certain conditions cease4 ,we have now to become acquainted with others1 which it is true are still to be considered as transient1 but which1 under certain circumstances1 become so fixed that1 even after the conditions which first occasioned their appearance cease1 they still remain1 and thus constitute the link between the physical and the chemical colours4 #dcj4 ,they appear from various causes on the surface of a colourless body1 originally1 without communication1 die or immersion 772 and we now proceed to trace them1 from their faintest indication to their most permanent state1 through the different conditions of their appearance1 which for easier survey we here at once summarily state4 #dca4 ,first condition4--,the contact of two smooth surfaces of hard transparent bodies4 ,first case3 if masses or plates of glass1 or if lenses are pressed against each other4 ,second case3 if a crack takes place in a solid mass of glass1 chrystal1 or ice4 ,third case3 if lamell of transparent stones become separated4 ,second condition4--,if a surface of glass or a polished stone is breathed upon4 ,third condition4--,the combination of the two last2 first1 breathing on the glass1 then placing another plate of glass upon it1 thus exciting the colours by pressure2 then removing the upper glass1 upon which the colours begin to fade and vanish with the breath4 ,fourth condition4--,bubbles of various liquids1 soap1 chocolate1 beer1 wine1 fine glass bubbles4 ,fifth condition4--,very fine pellicles and lamell1 produced by the decomposition of minerals and metals4 ,the pellicles of lime1 the surface of stagnant water1 especially if impregnated with iron1 and again pellicles of oil on water1 especially of varnish on aqua fortis4 ,sixth condition4--,if metals are heated2 the operation of imparting tints to steel and other metals4 ,seventh condition4--,if the surface of glass is beginning to decompose4 #dcb4 ,first condition1 first case4 ,if two convex glasses1 or a convex and plane glass1 or1 best of all1 a convex and concave glass come in contact1 concentric coloured circles appear4 ,the phenomenon exhibits itself immediately on the slightest pressure1 and may then be gradually carried through various successive states4 ,we will describe the complete appearance at once1 as we shall then be better enabled to follow the different states through which it passes4 #dcc4 ,the centre is colourless2 where the glasses are1 so to speak1 united in one by the strongest pressure1 a dark grey point appears with a silver white space round it3 then follow1 in decreasing distances1 various insulated rings1 all consisting of three colours1 which are in immediate contact with each other4 ,each of these rings1 of which perhaps three or four might be counted1 is yellow on the inner side1 blue on the outer1 and red in the centre4 ,between two rings there appears a silver white interval4 ,the rings which are farthest from the centre are always nearer together3 they are composed of red and green without a perceptible white space between them4 #dcd4 ,we will now observe the appearances in their gradual formation1 beginning from the slightest pressure4 #dce4 ,on the slightest pressure the centre itself appears of a green colour4 ,then follow as far as the concentric circles extend1 red and green rings4 ,they are wide1 accordingly1 and no trace of a silver white space is to be seen between them4 ,the green is produced by the blue of an imperfectly developed circle1 mixing with the yellow of the first circle4 ,all the remaining circles are1 in this slight contact1 broad2 their yellow and blue edges mix together1 thus producing a beautiful green4 ,the red1 however1 of each circle1 remains pure and untouched2 hence the whole series is composed of these two colours4 #dcf4 ,a somewhat stronger pressure separates the first circle by a slight interval from the imperfectly developed one3 it is thus detached1 and may be said to appear in a complete state4 ,the centre is now a blue point2 for the yellow of the first circle is now separated from this central point by a silver white space4 ,from the centre of the blue a red appears1 which is thus1 in all cases1 bounded on the outside by its blue edge4 ,the second and third rings from the centre are quite detached4 ,where deviations from this order present themselves1 the observer will be enabled to account for them1 from what has been or remains to be stated4 #dcg4 ,on a stronger pressure the centre becomes yellow2 this yellow is surrounded by a red and blue edge3 at last1 the yellow also retires from the centre2 the innermost circle is formed and is bounded with yellow4 ,the whole centre itself now appears silver white1 till at last1 on the strongest pressure1 the dark point appears1 and the phenomenon1 as described at first1 is complete4 #dch4 ,the relative size of the concentric circles and their intervals depends on the form of the glasses which are pressed together4 #dci4 ,we remarked above1 that the coloured centre is1 in fact1 an undeveloped circle4 ,it is1 however1 often found1 on the slightest pressure1 that several undeveloped circles exist there1 as it were1 in the germ2 these can be successively developed before the eye of the observer4 #ddj4 ,the regularity of these rings is owing to the form of the convex glasses1 and the diameter of the coloured appearance depends on the greater or lesser section of a circle on which a lens is polished4 ,we easily conclude from this1 that by pressing plane glasses together1 irregular appearances only will be produced2 the colours1 in fact1 undulate like watered silks1 and spread from the point of pressure in all directions4 ,yet1 the phenomenon as thus exhibited is much more splendid than in the former instance1 and cannot fail to strike every spectator4 ,if we make the experiment in this mode1 we shall distinctly see1 as in the other case1 that1 on a slight pressure1 the green and red waves appear2 on a stronger1 stripes of blue1 red1 and yellow1 become detached4 ,at first1 the outer sides of these stripes touch2 on increased pressure they are separated by a silver white space4 #dda4 ,before we proceed to a further description of this phenomenon1 we may point out the most convenient mode of exhibiting it4 ,place a large convex glass on a table near the window2 upon this glass lay a plate of well-polished mirror-glass1 about the size of a playing-card1 and the mere weight of the plate will press sufficiently to produce one or other of the phenomena above described4 ,so1 also1 by the different weight of plates of glass1 by other accidental circumstances1 for instance1 by slipping the plate on the side of the convex glass where the pressure cannot be so strong as in the centre1 all the gradations above described can be produced in succession4 #ddb4 ,in order to observe the phenomenon it is necessary to look obliquely on the surface where it appears4 ,but1 above all1 it is to be remarked that by stooping still more1 and looking at the appearance under a more acute angle1 the circles not only grow larger but other circles are developed from the centre1 of which no trace is to be discovered when we look perpendicularly1 even through the strongest magnifiers4 #ddc4 ,in order to exhibit the phenomenon in its greatest beauty1 the utmost attention should be paid to the cleanness of the glasses4 ,if the experiment is made with plate-glass adapted for mirrors1 the glass should be handled with gloves4 ,the inner surfaces1 which must come in contact with the utmost nicety1 may be most conveniently cleaned before the experiment1 and the outer surfaces should be kept clean while the pressure is increased4 #ddd4 ,from what has been said it will be seen that an exact contact of two smooth surfaces is necessary4 ,polished glasses are best adapted for the purpose4 ,plates of glass exhibit the most brilliant colours when they fit closely together1 and for this reason the phenomenon will increase in beauty if exhibited under an air-pump1 by exhausting the air4 #dde4 ,the appearance of the coloured rings may be produced in the greatest perfection by placing a convex and concave glass together which have been ground on similar segments of circles4 ,i have never seen the effect more brilliant than with the object-glass of an achromatic telescope1 in which the crown-glass and flint-glass were necessarily in the closest contact4 #ddf4 ,a remarkable appearance takes place when dissimilar surfaces are pressed together2 for example1 a polished crystal and a plate of glass4 ,the appearance does not at all exhibit itself in large flowing waves1 as in the combination of glass with glass1 but it is small and angular1 and1 as it were1 disjointed3 thus it appears that the surface of the polished crystal1 which consists of infinitely small sections of lamell1 does not come so uninterruptedly in contact with the glass as another glass-plate would4 #ddg4 ,the appearance of colour vanishes on the strongest pressure1 which so intimately unites the two surfaces that they appear to make but one substance4 ,it is this which occasions the dark centre1 because the pressed lens no longer reflects any light from this point1 for the very same point1 when seen against the light1 is perfectly clear and transparent4 ,on relaxing the pressure1 the colours1 in like manner1 gradually diminish1 and disappear entirely when the surfaces are separated4 #ddh4 ,these same appearances occur in two similar cases4 ,if entirely transparent masses become partially separated1 the surfaces of their parts being still sufficiently in contact1 we see the same circles and waves more or less4 ,they may be produced in great beauty by plunging a hot mass of glass in water2 the different fissures and cracks enabling us to observe the colours in various forms4 ,nature often exhibits the same phenomena in split rock crystals4 #ddi4 ,this appearance1 again1 frequently displays itself in the mineral world in those kinds of stone which by nature have a tendency to exfoliate4 ,these original lamell are1 it is true1 so intimately united1 that stones of this kind appear altogether transparent and colourless1 yet1 the internal layers become separated1 from various accidental causes1 without altogether destroying the contact3 thus the appearance1 which is now familiar to us by the foregoing description1 often occurs in nature1 particularly in calcareous spars2 the specularis1 adularia1 and other minerals of similar structure4 ,hence it shows an ignorance of the proximate causes of an appearance so often accidentally produced1 to consider it so important in mineralogy1 and to attach especial value to the specimens exhibiting it4 #dej4 ,we have yet to speak of the very remarkable inversion of this appearance1 as related by men of science4 ,if1 namely1 instead of looking at the colours by a reflected light1 we examine them by a transmitted light1 the opposite colours are said to appear1 and in a mode corresponding with that which we have before described as physiological2 the colours evoking each other4 ,instead of blue1 we should thus see red-yellow2 instead of red1 green1 c41 and vice vers4 ,we reserve experiments in detail1 the rather as we have ourselves still some doubts on this point4 #dea4 ,if we were now called upon to give some general explanation of these epoptical colours1 as they appear under the first condition1 and to show their connexion with the previously detailed physical phenomena1 we might proceed to do so as follows3-- #deb4 ,the glasses employed for the experiments are to be regarded as the utmost possible practical approach to transparence4 ,by the intimate contact1 however1 occasioned by the pressure applied to them1 their surfaces1 we are persuaded1 immediately become in a very slight degree dimmed4 ,within this semi-transparence the colours immediately appear1 and every circle comprehends the whole scale2 for when the two opposites1 yellow and blue1 are united by their red extremities1 pure red appears3 the green1 on the other hand1 as in prismatic experiments1 when yellow and blue touch4 #dec4 ,we have already repeatedly found that where colour exists at all1 the whole scale is soon called into existence2 a similar principle may be said to lurk in the nature of every physical phenomenon2 it already follows1 from the idea of polar opposition1 from which an elementary unity or completeness results4 #ded4 ,the fact that a colour exhibited by transmitted light is different from that displayed by reflected light1 reminds us of those dioptrical colours of the first class which we found were produced precisely in the same way through semi-opacity4 ,that here1 too1 a diminution of transparency exists there can scarcely be a doubt2 for the adhesion of the perfectly smooth plates of glass 7an adhesion so strong that they remain hanging to each other7 produces a degree of union which deprives each of the two surfaces1 in some degree1 of its smoothness and transparence4 ,the fullest proof may1 however1 be found in the fact that in the centre1 where the lens is most strongly pressed on the other glass1 and where a perfect union is accomplished1 a complete transparence takes place1 in which we no longer perceive any colour4 ,all this may be hereafter confirmed in a recapitulation of the whole4 #dee4 ,second condition4--,if after breathing on a plate of glass1 the breath is merely wiped away with the finger1 and if we then again immediately breathe on the glass1 we see very vivid colours gliding through each other2 these1 as the moisture evaporates1 change their place1 and at last vanish altogether4 ,if this operation is repeated1 the colours are more vivid and beautiful1 and remain longer than they did the first time4 #def4 ,quickly as this appearance passes1 and confused as it appears to be1 ,i have yet remarked the following effects3--,at first all the principal colours appear with their combinations2 on breathing more strongly1 the appearance may be perceived in some order4 ,in this succession it may be remarked1 that when the breath in evaporating becomes contracted from all sides towards the centre1 the blue colour vanishes last4 #deg4 ,the phenomenon appears most readily between the minute lines1 which the action of passing the fingers leaves on the clear surface2 a somewhat rough state of the surface of the glass is otherwise requisite4 ,on some glass the appearance may be produced by merely breathing2 in other cases the wiping with the fingers is necessary3 ,i have even met with polished mirror-glasses1 one side of which immediately showed the colours vividly2 the other not4 ,to judge from some remaining pieces1 the former was originally the front of the glass1 the latter the side which was covered with quicksilver4 #deh4 ,these experiments may be best made in cold weather1 because the glass may be more quickly and distinctly breathed upon1 and the breath evaporates more suddenly4 ,in severe frost the phenomenon may be observed on a large scale while travelling in a carriage2 the glasses being well cleaned1 and all closed4 ,the breath of the persons within is very gently diffused over the glass1 and immediately produces the most vivid play of colours4 ,how far they may present a regular succession ,i have not been able to remark2 but they appear particularly vivid when they have a dark object as a background4 ,this alternation of colours does not1 however1 last long2 for as soon as the breath gathers in drops1 or freezes to points of ice1 the appearance is at once at an end4 #dei4 ,third condition4--,the two foregoing experiments of the pressure and breathing may be united2 namely1 by breathing on a plate of glass1 and immediately after pressing the other upon it4 ,the colours then appear as in the case of two glasses unbreathed upon1 with this difference1 that the moisture occasions here and there an interruption of the undulations4 ,on pushing one glass away from the other the moisture appears iridescent as it evaporates4 #dfj4 ,it might1 however1 be asserted that this combined experiment exhibits no more than each single experiment2 for it appears the colours excited by pressure disappear in proportion as the glasses are less in contact1 and the moisture then evaporates with its own colours4 #dfa4 ,fourth condition4--,iridescent appearances are observable in almost all bubbles2 soap-bubbles are the most commonly known1 and the effect in question is thus exhibited in the easiest mode2 but it may be observed in wine1 beer1 in pure spirit1 and again1 especially1 in the froth of chocolate4 #dfb4 ,as in the above cases we required an infinitely narrow space between two surfaces which are in contact1 so we can consider the pellicle of the soap-bubble as an infinitely thin lamina between two elastic bodies2 for the appearance in fact takes place between the air within1 which distends the bubble1 and the atmospheric air4 #dfc4 ,the bubble when first produced is colourless2 then coloured stripes1 like those in marble paper1 begin to appear3 these at length spread over the whole surface1 or rather are driven round it as it is distended4 #dfd4 ,in a single bubble1 suffered to hang from the straw or tube1 the appearance of colour is difficult to observe1 for the quick rotation prevents any accurate observation1 and all the colours seem to mix together2 yet we can perceive that the colours begin at the orifice of the tube4 ,the solution itself may1 however1 be blown into carefully1 so that only one bubble shall appear4 ,this remains white 7colourless7 if not much agitated2 but if the solution is not too watery1 circles appear round the perpendicular axis of the bubble2 these being near each other1 are commonly composed alternately of green and red4 ,lastly1 several bubbles may be produced together by the same means2 in this case the colours appear on the sides where two bubbles have pressed each other flat4 #dfe4 ,the bubbles of chocolate-froth may perhaps be even more conveniently observed than those of soap2 though smaller1 they remain longer4 ,in these1 owing to the heat1 an impulse1 a movement1 is produced and sustained1 which appears necessary to the development and succession of the appearances4 #dff4 ,if the bubble is small1 or shut in between others1 coloured lines chase each other over the surface1 resembling marbled paper2 all the colours of the scale are seen to pass through each other2 the pure1 the augmented1 the combined1 all distinctly clear and beautiful4 ,in small bubbles the appearance lasts for a considerable time4 #dfg4 ,if the bubble is larger1 or if it becomes by degrees detached1 owing to the bursting of others near1 we perceive that this impulsion and attraction of the colours has1 as it were1 an end in view2 for on the highest point of the bubble we see a small circle appear1 which is yellow in the centre2 the other remaining coloured lines move constantly round this with a vermicular action4 #dfh4 ,in a short time the circle enlarges and sinks downwards on all sides2 in the centre the yellow remains2 below and on the outside it becomes red1 and soon blue2 below this again appears a new circle of the same series of colours3 if they approximate sufficiently1 a green is produced by the union of the border-colours4 #dfi4 ,when ,i could count three such leading circles1 the centre was colourless1 and this space became by degrees larger as the circles sank lower1 till at last the bubble burst4 #dgj4 ,fifth condition4--,very delicate pellicles may be formed in various ways3 on these films we discover a very lively play of colours1 either in the usual order1 or more confusedly passing through each other4 ,the water in which lime has been slaked soon skims over with a coloured pellicle3 the same happens on the surface of stagnant water1 especially if impregnated with iron4 ,the lamell of the fine tartar which adheres to bottles1 especially in red ,french wine1 exhibit the most brilliant colours1 on being exposed to the light1 if carefully detached4 ,drops of oil on water1 brandy1 and other fluids1 produce also similar circles and brilliant effects3 but the most beautiful experiment that can be made is the following3--,let aqua fortis1 not too strong1 be poured into a flat saucer1 and then with a brush drop on it some of the varnish used by engravers to cover certain portions during the process of biting their plates4 ,after quick commotion there presently appears a film which spreads itself out in circles1 and immediately produces the most vivid appearances of colour4 #dga4 ,sixth condition4--,when metals are heated1 colours rapidly succeeding each other appear on the surface3 these colours can1 however1 be arrested at will4 #dgb4 ,if a piece of polished steel is heated1 it will1 at a certain degree of warmth1 be overspread with yellow4 ,if taken suddenly away from the fire1 this yellow remains4 #dgc4 ,as the steel becomes hotter1 the yellow appears darker1 intenser1 and presently passes into red4 ,this is difficult to arrest1 for it hastens very quickly to bright blue4 #dgd4 ,this beautiful blue is to be arrested if the steel is suddenly taken out of the heat and buried in ashes4 ,the blue steel works are produced in this way4 ,if1 again1 the steel is held longer over the fire1 it soon becomes a light blue1 and so it remains4 #dge4 ,these colours pass like a breath over the plate of steel2 each seems to fly before the other1 but1 in reality1 each successive hue is constantly developed from the preceding one4 #dgf4 ,if we hold a penknife in the flame of a light1 a coloured stripe will appear across the blade4 ,the portion of the stripe which was nearest to the flame is light blue2 this melts into blue-red2 the red is in the centre2 then follow yellow-red and yellow4 #dgg4 ,this phenomenon is deducible from the preceding ones2 for the portion of the blade next the handle is less heated than the end which is in the flame1 and thus all the colours which in other cases exhibited themselves in succession1 must here appear at once1 and may thus be permanently preserved4 #dgh4 ,robert ,boyle gives this succession of colours as follows3--,a florido flavo ad flavum saturum et rubescentem 7quem artifices sanguineum vocant7 inde ad languidum1 postea ad saturiorem cyaneum4 ,this would be quite correct if the words languidus and saturior were to change places4 ,how far the observation is correct1 that the different colours have a relation to the degree of temper which the metal afterwards acquires1 we leave to others to decide4 ,the colours are here only indications of the different degrees of heat4--,note ,r4 #dgi4 ,when lead is calcined1 the surface is first greyish4 ,this greyish powder1 with greater heat1 becomes yellow1 and then orange4 ,silver1 too1 exhibits colours when heated2 the fracture of silver in the process of refining belongs to the same class of examples4 ,when metallic glasses melt1 colours in like manner appear on the surface4 #dhj4 ,seventh condition4--,when the surface of glass becomes decomposed4 ,the accidental opacity 7blindwerden7 of glass has been already noticed3 the term 7blindwerden7 is employed to denote that the surface of the glass is so affected as to appear dim to us4 #dha4 ,white glass becomes blind soonest2 cast1 and afterwards polished glass is also liable to be so affected2 the bluish less1 the green least4 #dhb4 ,of the two sides of a plate of glass one is called the mirror side2 it is that which in the oven lies uppermost1 on which one may observe roundish elevations3 it is smoother than the other1 which is undermost in the oven1 and on which scratches may be sometimes observed4 ,on this account the mirror side is placed facing the interior of rooms1 because it is less affected by the moisture adhering to it from within1 than the other would be1 and the glass is thus less liable to become blind4 #dhc4 ,this half-opacity or dimness of the glass assumes by degrees an appearance of colour which may become very vivid1 and in which perhaps a certain succession1 or otherwise regular order1 might be discovered4 #dhd4 ,having thus traced the physical colours from their simplest effects to the present instances1 where these fleeting appearances are found to be fixed in bodies1 we are1 in fact1 arrived at the point where the chemical colours begin2 nay1 we have in some sort already passed those limits2 a circumstance which may excite a favourable prejudice for the consistency of our statement4 ,by way of conclusion to this part of our inquiry1 we subjoin a general observation1 which may not be without its bearing on the common connecting principle of the phenomena that have been adduced4 #dhe4 ,the colouring of steel and the appearances analogous to it1 might perhaps be easily deduced from the doctrine of the semi-opaque mediums4 ,polished steel reflects light powerfully3 we may consider the colour produced by the heat as a slight degree of dimness3 hence a bright yellow must immediately appear2 this1 as the dimness increases1 must still appear deeper1 more condensed1 and redder1 and at last pure and ruby-red4 ,the colour has now reached the extreme point of depth1 and if we suppose the same degree of semi-opacity still to continue1 the dimness would now spread itself over a dark ground1 first producing a violet1 then a dark-blue1 and at last a light-blue1 and thus complete the series of the appearances4 ,we will not assert that this mode of explanation will suffice in all cases2 our object is rather to point out the road by which the all-comprehensive formula1 the very key of the enigma1 may be at last discovered4--,note ,s4 ,,part ,,iii4 ,,chemical ,,colours4 #dhf4 ,we give this denomination to colours which we can produce1 and more or less fix1 in certain bodies2 which we can render more intense1 which we can again take away and communicate to other bodies1 and to which1 therefore1 we ascribe a certain permanency3 duration is their prevailing characteristic4 #dhg4 ,in this view the chemical colours were formerly distinguished with various epithets2 they were called colores proprii1 corporei1 materiales1 veri1 permanentes1 fixi4 #dhh4 ,in the preceding chapter we observed how the fluctuating and transient nature of the physical colours becomes gradually fixed1 thus forming the natural transition to our present subject4 #dhi4 ,colour becomes fixed in bodies more or less permanently2 superficially1 or thoroughly4 #dij4 ,all bodies are susceptible of colour2 it can either be excited1 rendered intense1 and gradually fixed in them1 or at least communicated to them4 ,,xxxiv4 ,,chemical ,,contrast4 #dia4 ,in the examination of coloured appearances we had occasion everywhere to take notice of a principle of contrast3 so again1 in approaching the precincts of chemistry1 we find a chemical contrast of a remarkable nature4 ,we speak here1 with reference to our present purpose1 only of that which is comprehended under the general names of acid and alkali4 #dib4 ,we characterised the chromatic contrast1 in conformity with all other physical contrasts as a more and less2 ascribing the plus to the yellow side1 the minus to the blue2 and we now find that these two divisions correspond with the chemical contrasts4 ,the yellow and yellow-red affect the acids1 the blue and blue-red the alkalis2 thus the phenomena of chemical colours1 although still necessarily mixed up with other considerations1 admit of being traced with sufficient simplicity4 #dic4 ,the principal phenomena in chemical colours are produced by the oxydation of metals1 and it will be seen how important this consideration is at the outset4 ,other facts which come into the account1 and which are worthy of attention1 will be examined under separate heads2 in doing this we1 however1 expressly state that we only propose to offer some preparatory suggestions to the chemist in a very general way1 without entering into the nicer chemical problems and questions1 or presuming to decide on them4 ,our object is only to give a sketch of the mode in which1 according to our conviction1 the chemical theory of colours may be connected with general physics4 ,,xxxv4 ,,white4 #did4 ,in treating of the dioptrical colours of the first class 7#aee7 we have already in some degree anticipated this subject4 ,transparent substances may be said to be in the highest class of inorganic matter4 ,with these1 colourless semi-transparence is closely connected1 and white may be considered the last opaque degree of this4 #die4 ,pure water crystallised to snow appears white1 for the transparence of the separate parts makes no transparent whole4 ,various crystallised salts1 when deprived to a certain extent of moisture1 appear as a white powder4 ,the accidentally opaque state of a pure transparent substance might be called white2 thus pounded glass appears as a white powder4 ,the cessation of a combining power1 and the exhibition of the atomic quality of the substance might at the same time be taken into the account4 #dif4 ,the known undecomposed earths are1 in their pure state1 all white4 ,they pass to a state of transparence by natural crystallization4 ,silex becomes rock-crystal2 argile1 mica2 magnesia1 talc2 calcareous earth and barytes appear transparent in various spars4--,note ,t4 #dig4 ,as in the colouring of mineral bodies the metallic oxydes will often invite our attention1 we observe1 in conclusion1 that metals1 when slightly oxydated1 at first appear white1 as lead is converted to white lead by vegetable acid4 ,,xxxvi4 ,,black4 #dih4 ,black is not exhibited in so elementary a state as white4 ,we meet with it in the vegetable kingdom in semi-combustion2 and charcoal1 a substance especially worthy of attention on other accounts1 exhibits a black colour4 ,again1 if woods--for example1 boards1 owing to the action of light1 air1 and moisture1 are deprived in part of their combustibility1 there appears first the grey then the black colour4 ,so again1 we can convert even portions of animal substance to charcoal by semi-combustion4 #dii4 ,in the same manner we often find that a sub-oxydation takes place in metals when the black colour is to be produced4 ,various metals1 particularly iron1 become black by slight oxydation1 by vinegar1 by mild acid fermentations2 for example1 a decoction of rice1 c4 #ejj4 ,again1 it may be inferred that a de-oxydation may produce black4 ,this occurs in the preparation of ink1 which becomes yellow by the solution of iron in strong sulphuric acid1 but when partly de-oxydised by the infusion of gall-nuts1 appears black4 ,,xxxvii4 ,,first ,,excitation ,,of ,,colour4 #eja4 ,in the division of physical colours1 where semi-transparent mediums were considered1 we saw colours antecedently to white and black4 ,in the present case we assume a white and black already produced and fixed2 and the question is1 how colour can be excited in them8 #ejb4 ,here1 too1 we can say1 white that becomes darkened or dimmed inclines to yellow2 black1 as it becomes lighter1 inclines to blue4--,note ,u4 #ejc4 ,yellow appears on the active 7plus7 side1 immediately in the light1 the bright1 the white4 ,all white surfaces easily assume a yellow tinge2 paper1 linen1 wool1 silk1 wax3 transparent fluids again1 which have a tendency to combustion1 easily become yellow2 in other words they easily pass into a very slight state of semi-transparence4 #ejd4 ,so again the excitement on the passive side1 the tendency to obscure1 dark1 black1 is immediately accompanied with blue1 or rather with a reddish-blue4 ,iron dissolved in sulphuric acid1 and much diluted with water1 if held to the light in a glass1 exhibits a beautiful violet colour as soon as a few drops only of the infusion of gall-nuts are added4 ,this colour presents the peculiar hues of the dark topaz1 the orphninon of a burnt-red1 as the ancients expressed it4 #eje4 ,whether any colour can be excited in the pure earths by the chemical operations of nature and art1 without the admixture of metallic oxydes1 is an important question1 generally1 indeed1 answered in the negative4 ,it is perhaps connected with the question--to what extent changes may be produced in the earths through oxydation8 #ejf4 ,undoubtedly the negation of the above question is confirmed by the circumstance that wherever mineral colours are found1 some trace of metal1 especially of iron1 shows itself2 we are thus naturally led to consider how easily iron becomes oxydised1 how easily the oxyde of iron assumes different colours1 how infinitely divisible it is1 and how quickly it communicates its colour4 ,it were to be wished1 notwithstanding1 that new experiments could be made in regard to the above point1 so as either to confirm or remove any doubt4 #ejg4 ,however this may be1 the susceptibility of the earths with regard to colours already existing is very great2 aluminous earth is thus particularly distinguished4 #ejh4 ,in proceeding to consider the metals1 which in the inorganic world have the almost exclusive prerogative of appearing coloured1 we find that1 in their pure1 independent1 natural state1 they are already distinguished from the pure earths by a tendency to some one colour or other4 #eji4 ,while silver approximates most to pure white1--nay1 really represents pure white1 heightened by metallic splendour1--steel1 tin1 lead1 and so forth1 incline towards pale blue-grey2 gold1 on the other hand1 deepens to pure yellow1 copper approaches a red hue1 which1 under certain circumstances1 increases almost to bright red1 but which again returns to a yellow golden colour when combined with zinc4 #eaj4 ,but if metals in their pure state have so specific a determination towards this or that exhibition of colour1 they are1 through the effect of oxydation1 in some degree reduced to a common character2 for the elementary colours now come forth in their purity1 and although this or that metal appears to have a particular tendency to this or that colour1 we find some that can go through the whole circle of hues1 others1 that are capable of exhibiting more than one colour2 tin1 however1 is distinguished by its comparative inaptitude to become coloured4 ,we propose to give a table hereafter1 showing how far the different metals can be more or less made to exhibit the different colours4 #eaa4 ,when the clean1 smooth surface of a pure metal1 on being heated1 becomes overspread with a mantling colour1 which passes through a series of appearances as the heat increases1 this1 we are persuaded1 indicates the aptitude of the metal to pass through the whole range of colours4 ,we find this phenomenon most beautifully exhibited in polished steel2 but silver1 copper1 brass1 lead1 and tin1 easily present similar appearances4 ,a superficial oxydation is probably here taking place1 as may be inferred from the effects of the operation when continued1 especially in the more easily oxydizable metals4 #eab4 ,the same conclusion may be drawn from the fact that iron is more easily oxydizable by acid liquids when it is red hot1 for in this case the two effects concur with each other4 ,we observe1 again1 that steel1 accordingly as it is hardened in different stages of its colorification1 may exhibit a difference of elasticity3 this is quite natural1 for the various appearances of colour indicate various degrees of heat4#a #eac4 ,if we look beyond this superficial mantling1 this pellicle of colour1 we observe that as metals are oxydized throughout their masses1 white or black appears with the first degree of heat1 as may be seen in white lead1 iron1 and quicksilver4 #ead4 ,if we examine further1 and look for the actual exhibition of colour1 we find it most frequently on the plus side4 ,the mantling1 so often mentioned1 of smooth metallic surfaces begins with yellow4 ,iron passes presently into yellow ochre1 lead from white lead to massicot1 quicksilver from thiops to yellow turbith4 ,the solutions of gold and platinum in acids are yellow4 #eae4 ,the exhibitions on the minus side are less frequent4 ,copper slightly oxydized appears blue4 ,in the preparation of ,prussian-blue1 alkalis are employed4 #eaf4 ,generally1 however1 these appearances of colour are of so mutable a nature that chemists look upon them as deceptive tests1 at least in the nicer gradations4 ,for ourselves1 as we can only treat of these matters in a general way1 we merely observe that the appearances of colour in metals may be classed according to their origin1 manifold appearance1 and cessation1 as various results of oxydation1 hyper-oxydation1 ab-oxydation1 and de-oxydation4#b #a ,see par4 #dgh4 #b ,as these terms are afterwards referred to 7par4 #ebe71 it was necessary to preserve them4 ,,xxxviii4 ,,augmentation ,,of ,,colour4#a #eag4 ,the augmentation of colour exhibits itself as a condensation1 a fulness1 a darkening of the hue4 ,we have before seen1 in treating of colourless mediums1 that by increasing the degree of opacity in the medium1 we can deepen a bright object from the lightest yellow to the intensest ruby-red4 ,blue1 on the other hand1 increases to the most beautiful violet1 if we rarefy and diminish a semi-opaque medium1 itself lighted1 but through which we see darkness 7#aej1 #aea74 #eah4 ,if the colour is positive1 a similar colour appears in the intenser state4 ,thus if we fill a white porcelain cup with a pure yellow liquor1 the fluid will appear to become gradually redder towards the bottom1 and at last appears orange4 ,if we pour a pure blue solution into another cup1 the upper portion will exhibit a sky-blue1 that towards the bottom1 a beautiful violet4 ,if the cup is placed in the sun1 the shadowed side1 even of the upper portion1 is already violet4 ,if we throw a shadow with the hand1 or any other substance1 over the illumined portion1 the shadow in like manner appears reddish4 #eai4 ,this is one of the most important appearances connected with the doctrine of colours1 for we here manifestly find that a difference of quantity produces a corresponding qualified impression on our senses4 ,in speaking of the last class of epoptical colours 7#deb1 #dhe71 we stated our conjecture that the colouring of steel might perhaps be traced to the doctrine of the semi-transparent mediums1 and we would here again recall this to the reader's recollection4 #ebj4 ,all chemical augmentation of colour1 again1 is the immediate consequence of continued excitation4 ,the augmentation advances constantly and unremittingly1 and it is to be observed that the increase of intenseness is most common on the plus side4 ,yellow iron ochre increases1 as well by fire as by other operations1 to a very strong red3 massicot is increased to red lead1 turbith to vermilion1 which last attains a very high degree of the yellow-red4 ,an intimate saturation of the metal by the acid1 and its separation to infinity1 take place together with the above effects4 #eba4 ,the augmentation on the minus side is less frequent2 but we observe that the more pure and condensed the ,prussian-blue or cobalt glass is prepared1 the more readily it assumes a reddish hue and inclines to the violet4 #ebb4 ,the ,french have a happy expression for the less perceptible tendency of yellow and blue towards red3 they say the colour has un il de rouge1 which we might perhaps express by a reddish glance 7einen rthlichen blick74 #a ,steigerung1 literally gradual ascent4 ,see the note to par4 #ebc4 ,,xxxix4 ,,culmination#a #ebc4 ,this is the consequence of still progressing augmentation4 ,red1 in which neither yellow nor blue is to be detected1 here constitutes the acme4 #ebd4 ,if we wish to select a striking example of a culmination on the plus side1 we again find it in the coloured steel1 which attains the bright red acme1 and can be arrested at this point4 #ebe4 ,were we here to employ the terminology before proposed1 we should say that the first oxydation produces yellow1 the hyper-oxydation yellow-red2 that here a kind of maximum exists1 and that then an ab-oxydation1 and lastly a de-oxydation takes place4 #ebf4 ,high degrees of oxydation produce a bright red4 ,gold in solution1 precipitated by a solution of tin1 appears bright red3 oxyde of arsenic1 in combination1 with sulphur1 produces a ruby colour4 #ebg4 ,how far1 however1 a kind of sub-oxydation may co-operate in some culminations1 is matter for inquiry2 for an influence of alkalis on yellow-red also appears to produce the culmination2 the colour reaching the acme by being forced towards the minus side4 #ebh4 ,the ,dutch prepare a colour known by the name of vermilion1 from the best ,hungarian cinnabar1 which exhibits the brightest yellow-red4 ,this vermilion is still only a cinnabar1 which1 however1 approximates the pure red1 and it may be conjectured that alkalis are used to bring it nearer to the culminating point4 #ebi4 ,vegetable juices1 treated in this way1 offer very striking examples of the above effects4 ,the colouring-matter of turmeric1 annotto1 dyer's saffron1#b and other vegetables1 being extracted with spirits of wine1 exhibits tints of yellow1 yellow-red1 and hyacinth-red2 these1 by the admixture of alkalis1 pass to the culminating point1 and even beyond it to blue-red4 #ecj4 ,no instance of a culmination on the minus side has come to my knowledge in the mineral and vegetable kingdoms4 ,in the animal kingdom the juice of the murex is remarkable2 of its augmentation and culmination on the minus side1 we shall hereafter have occasion to speak4 #a ,culmination1 the original word4 ,it might have been rendered maximum of colour1 but as the author supposes an ascent through yellow and blue to red1 his meaning is better expressed by his own term4 #b ,curcuma1 ,bixa ,orellana1 ,carthamus ,tinctorius4 ,,xl4 ,,fluctuation4 #eca4 ,the mutability of colour is so great1 that even those pigments1 which may have been considered to be defined and arrested1 still admit of slight variations on one side or the other4 ,this mutability is most remarkable near the culminating point1 and is effected in a very striking manner by the alternate employment of acids and alkalis4 #ecb4 ,to express this appearance in dyeing1 the ,french make use of the word virer1 to turn from one side to the other2 they thus very adroitly convey an idea which others attempt to express by terms indicating the component hues4 #ecc4 ,the effect produced with litmus is one of the most known and striking of this kind4 ,this colouring substance is tendered red-blue by means of alkalis4 ,the red-blue is very readily changed to red-yellow by means of acids1 and again returns to its first state by again employing alkalis4 ,the question whether a culminating point is to be discovered and arrested by nice experiments1 is left to those who are practised in these operations4 ,dyeing1 especially scarlet-dyeing1 might afford a variety of examples of this fluctuation4 ,,xli4 ,,passage ,,through ,,the ,,whole ,,scale4 #ecd4 ,the first excitation and gradual increase of colour take place more on the plus than on the minus side4 ,so1 also1 in passing through the whole scale1 colour exhibits itself most on the plus side4 #ece4 ,a passage of this kind1 regular and evident to the senses1 from yellow through red to blue1 is apparent in the colouring of steel4 #ecf4 ,the metals may be arrested at various points of the colorific circle by various degrees and kinds of oxydation4 #ecg4 ,as they also appear green1 a question arises whether chemists know any instance in the mineral kingdom of a constant transition from yellow1 through green1 to blue1 and vice vers4 ,oxyde of iron1 melted with glass1 produces first a green1 and with a more powerful heat1 a blue colour4 #ech4 ,we may here observe of green generally1 that it appears1 especially in an atomic sense1 and certainly in a pure state1 when we mix blue and yellow3 but1 again1 an impure and dirty yellow soon gives us the impression of green2 yellow and black already produce green2 this1 however1 is owing to the affinity between black and blue4 ,an imperfect yellow1 such as that of sulphur1 gives us the impression of a greenish hue3 thus1 again1 an imperfect blue appears green4 ,the green of wine bottles arises1 it appears1 from an imperfect union of the oxyde of iron with the glass4 ,if we produce a more complete union by greater heat1 a beautiful blue-glass is the result4 #eci4 ,from all this it appears that a certain chasm exists in nature between yellow and blue1 the opposite characters of which1 it is true1 may be done away atomically by due immixture1 and1 thus combined1 to green2 but the true reconciliation between yellow and blue1 it seems1 only takes place by means of red4 #edj4 ,the process1 however1 which appears unattainable in inorganic substances1 we shall find to be possible when we turn our attention to organic productions2 for in these1 the passage through the whole circle from yellow1 through green and blue1 to red1 really takes place4 ,,xlii4 ,,inversion4 #eda4 ,again1 an immediate inversion or change to the totally opposite hue1 is a very remarkable appearance which sometimes occurs2 at present1 we are merely enabled to adduce what follows4 #edb4 ,the mineral chameleon1 a name which has been given to an oxyde of manganese1 may be considered1 in its perfectly dry state1 as a green powder4 ,if we strew it in water1 the green colour displays itself very beautifully in the first moment of solution1 but it changes presently to the bright red opposite to green1 without any apparent intermediate state4 #edc4 ,the same occurs with the sympathetic ink1 which may be considered a reddish liquid1 but which1 when dried by warmth1 appears as a green colour on paper4 #edd4 ,in fact1 this phenomenon appears to be owing to the conflict between a dry and moist state1 as has been already observed1 if we are not mistaken1 by the chemists4 ,we may look to the improvements of time to point out what may further be deduced from these phenomena1 and to show what other facts they may be connected with4 ,,xliii4 ,,fixation4 #ede4 ,mutable as we have hitherto found colour to be1 even as a substance1 yet under certain circumstances it may at last be fixed4 #edf4 ,there are bodies capable of being entirely converted into colouring matter3 here it may be said that the colour fixes itself in its own substance1 stops at a certain point1 and is there defined4 ,such colouring substances are found throughout nature2 the vegetable world affords a great quantity of examples1 among which some are particularly distinguished1 and may be considered as the representatives of the rest2 such as1 on the active side1 madder1 on the passive side1 indigo4 #edg4 ,in order to make these materials available in use1 it is necessary that the colouring quality in them should be intimately condensed1 and the tinging substance refined1 practically speaking1 to an infinite divisibility4 ,this is accomplished in various ways1 and particularly by the well-known means of fermentation and decomposition4 #edh4 ,these colouring substances now attach themselves again to other bodies4 ,thus1 in the mineral kingdom they adhere to earths and metallic oxydes2 they unite in melting with glasses2 and in this case1 as the light is transmitted through them1 they appear in the greatest beauty1 while an eternal duration may be ascribed to them4 #edi4 ,they fasten on vegetable and animal bodies with more or less power1 and remain more or less permanently2 partly owing to their nature1--as yellow1 for instance1 is more evanescent than blue1--or owing to the nature of the substance on which they appear4 ,they last less in vegetable than in animal substances1 and even within this latter kingdom there are again varieties4 ,hemp or cotton threads1 silk or wool1 exhibit very different relations to colouring substances4 #eej4 ,here comes into the account the important operation of employing mordants1 which may be considered as the intermediate agents between the colour and the recipient substance2 various works on dyeing speak of this circumstantially4 ,suffice it to have alluded to processes by means of which the colour retains a permanency only to be destroyed with the substance1 and which may even increase in brightness and beauty by use4 ,,xliv4 ,,intermixture1 ,,real4 #eea4 ,every intermixture pre-supposes a specific state of colour2 and thus when we speak of intermixture1 we here understand it in an atomic sense4 ,we must first have before us certain bodies arrested at any given point of the colorific circle1 before we can produce gradations by their union4 #eeb4 ,yellow1 blue1 and red1 may be assumed as pure elementary colours1 already existing2 from these1 violet1 orange1 and green1 are the simplest combined results4 #eec4 ,some persons have taken much pains to define these intermixtures more accurately1 by relations of number1 measure1 and weight1 but nothing very profitable has been thus accomplished4 #eed4 ,painting consists1 strictly speaking1 in the intermixture of such specific colouring bodies and their infinite possible combinations--combinations which can only be appreciated by the nicest1 most practised eye1 and only accomplished under its influence4 #eee4 ,the intimate combination of these ingredients is effected1 in the first instance1 through the most perfect comminution of the material by means of grinding1 washing1 c41 as well as by vehicles or liquid mediums which hold together the pulverized substance1 and combine organically1 as it were1 the unorganic2 such are the oils1 resins1 c4--,note ,v4 #eef4 ,if all the colours are mixed together they retain their general character as 1 and as they are no longer seen next each other1 no completeness1 no harmony1 is experienced2 the result is grey1 which1 like apparent colour1 always appears somewhat darker than white1 and somewhat lighter than black4 #eeg4 ,this grey may be produced in various ways4 ,by mixing yellow and blue to an emerald green1 and then adding pure red1 till all three neutralize each other2 or1 by placing the primitive and intermediate colours next each other in a certain proportion1 and afterwards mixing them4 #eeh4 ,that all the colours mixed together produce white1 is an absurdity which people have credulously been accustomed to repeat for a century1 in opposition to the evidence of their senses4 #eei4 ,colours when mixed together retain their original darkness4 ,the darker the colours1 the darker will be the grey resulting from their union1 till at last this grey approaches black4 ,the lighter the colours the lighter will be the grey1 which at last approaches white4 ,,xlv4 ,,intermixture1 ,,apparent4 #efj4 ,the intermixture1 which is only apparent1 naturally invites our attention in connexion with the foregoing2 it is in many respects important1 and1 indeed1 the intermixture which we have distinguished as real1 might be considered as merely apparent4 ,for the elements of which the combined colour consists are only too small to be considered as distinct parts4 ,yellow and blue powders mingled together appear green to the naked eye1 but through a magnifying glass we can still perceive yellow and blue distinct from each other4 ,thus yellow and blue stripes seen at a distance1 present a green mass2 the same observation is applicable with regard to the intermixture of other specific colours4 #efa4 ,in the description of our apparatus we shall have occasion to mention the wheel by means of which the apparent intermixture is produced by rapid movement4 ,various colours are arranged near each other round the edge of a disk1 which is made to revolve with velocity1 and thus by having several such disks ready1 every possible intermixture can be presented to the eye1 as well as the mixture of all colours to grey1 darker or lighter1 according to the depth of the tints as above explained4 #efb4 ,physiological colours admit1 in like manner1 of being mixed with others4 ,if1 for example1 we produce the blue shadow 7#fe7 on a light yellow paper1 the surface will appear green4 ,the same happens with regard to the other colours if the necessary preparations are attended to4 #efc4 ,if1 when the eye is impressed with visionary images that last for a while1 we look on coloured surfaces1 an intermixture also takes place2 the spectrum is determined to a new colour which is composed of the two4 #efd4 ,physical colours also admit of combination4 ,here might be adduced the experiments in which many-coloured images are seen through the prism1 as we have before shown in detail 7#beh1 #bhd74 #efe4 ,those who have prosecuted these inquiries have1 however1 paid most attention to the appearances which take place when the prismatic colours are thrown on coloured surfaces4 #eff4 ,what is seen under these circumstances is quite simple4 ,in the first place it must be remembered that the prismatic colours are much more vivid than the colours of the surface on which they are thrown4 ,secondly1 we have to consider that the prismatic colours may be either homogeneous or heterogeneous1 with the recipient surface4 ,in the former case the surface deepens and enhances them1 and is itself enhanced in return1 as a coloured stone is displayed by a similarly coloured foil4 ,in the opposite case each vitiates1 disturbs1 and destroys the other4 #efg4 ,these experiments may be repeated with coloured glasses1 by causing the sun-light to shine through them on coloured surfaces4 ,in every instance similar results will appear4 #efh4 ,the same effect takes place when we look on coloured objects through coloured glasses2 the colours being thus according to the same conditions enhanced1 subdued1 or neutralized4 #efi4 ,if the prismatic colours are suffered to pass through coloured glasses1 the appearances that take place are perfectly analogous2 in these cases more or less force1 more or less light and dark1 the clearness and cleanness of the glass are all to be allowed for1 as they produce many delicate varieties of effect3 these will not escape the notice of every accurate observer who takes sufficient interest in the inquiry to go through the experiments4 #egj4 ,it is scarcely necessary to mention that several coloured glasses1 as well as oiled or transparent papers1 placed over each other1 may be made to produce and exhibit every kind of intermixture at pleasure4 #ega4 ,lastly1 the operation of glazing in painting belongs to this kind of intermixture2 by this means a much more refined union may be produced than that arising from the mechanical1 atomic mixture which is commonly employed4 ,,xlvi4 ,,communication1 ,,actual4 #egb4 ,having now provided the colouring materials1 as before shown1 a further question arises how to communicate these to colourless substances3 the answer is of the greatest importance from the connexion of the object with the ordinary wants of men1 with useful purposes1 and with commercial and technical interests4 #egc4 ,here1 again1 the dark quality of every colour again comes into the account4 ,from a yellow1 that is very near to white1 through orange1 and the hue of minium to pure red and carmine1 through all gradations of violet to the deepest blue which is almost identified with black1 colour still increases in darkness4 ,blue once defined1 admits of being diluted1 made light1 united with yellow1 and then1 as green1 it approaches the light side of the scale3 but this is by no means according to its own nature4 #egd4 ,in the physiological colours we have already seen that they are less than the light1 inasmuch as they are a repetition of an impression of light1 nay1 at last they leave this impression quite as a dark4 ,in physical experiments the employment of semi-transparent mediums1 the effect of semi-transparent accessory images1 taught us that in such cases we have to do with a subdued light1 with a transition to darkness4 #ege4 ,in treating of the chemical origin of pigments we found that the same effect was produced on the very first excitement4 ,the yellow tinge which mantles over the steel1 already darkens the shining surface4 ,in changing white lead to massicot it is evident that the yellow is darker than white4 #egf4 ,this process is in the highest degree delicate2 the growing intenseness1 as it still increases1 tinges the substance more and more intimately and powerfully1 and thus indicates the extreme fineness1 and the infinite divisibility of the coloured atoms4 #egg4 ,the colours which approach the dark side1 and consequently1 blue in particular1 can be made to approximate to black2 in fact1 a very perfect ,prussian blue1 or an indigo acted on by vitriolic acid appears almost as a black4 #egh4 ,a remarkable appearance may be here adverted to2 pigments1 in their deepest and most condensed state1 especially those produced from the vegetable kingdom1 such as the indigo just mentioned1 or madder carried to its intensest hue1 no longer show their own colour2 on the contrary1 a decided metallic shine is seen on their surface1 in which the physiological compensatory colour appears4 #egi4 ,all good indigo exhibits a copper-colour in its fracture1 a circumstance attended to1 as a known characteristic1 in trade4 ,again1 the indigo which has been acted on by sulphuric acid1 if thickly laid on1 or suffered to dry so that neither white paper nor the porcelain can appear through1 exhibits a colour approaching to orange4 #ehj4 ,the bright red ,spanish rouge1 probably prepared from madder1 exhibits on its surface a perfectly green1 metallic shine4 ,if this colour1 or the blue before mentioned1 is washed with a pencil on porcelain or paper1 it is seen in its real state owing to the bright ground shining through4 #eha4 ,coloured liquids appear black when no light is transmitted through them1 as we may easily see in cubic tin vessels with glass bottoms4 ,in these every transparent-coloured infusion will appear black and colourless if we place a black surface under them4 #ehb4 ,if we contrive that the image of a flame be reflected from the bottom1 the image will appear coloured4 ,if we lift up the vessel and suffer the transmitted light to fall on white paper under it1 the colour of the liquid appears on the paper4 ,every light ground seen through such a coloured medium exhibits the colour of the medium4 #ehc4 ,thus every colour1 in order to be seen1 must have a light within or behind it4 ,hence the lighter and brighter the grounds are1 the more brilliant the colours appear4 ,if we pass lac-varnish over a shining white metal surface1 as the so-called foils are prepared1 the splendour of the colour is displayed by this internally reflected light as powerfully as in any prismatic experiment2 nay1 the force of the physical colours is owing principally to the circumstance that light is always acting with and behind them4 #ehd4 ,lichtenberg1 who of necessity followed the received theory1 owing to the time and circumstances in which he lived1 was yet too good an observer1 and too acute not to explain and classify1 after his fashion1 what was evident to his senses4 ,he says1 in the preface to ,delaval1 ,it appears to me also1 on other grounds1 probable1 that our organ1 in order to be impressed by a colour1 must at the same time be impressed by all light 7white74 #ehe4 ,to procure white as a ground is the chief business of the dyer4 ,every colour may be easily communicated to colourless earths1 especially to alum3 but the dyer has especially to do with animal and vegetable products as the ground of his operations4 #ehf4 ,everything living tends to colour--to local1 specific colour1 to effect1 to opacity--pervading the minutest atoms4 ,everything in which life is extinct approximates to white 7#did71 to the abstract1 the general state1 to clearness#a1 to transparence4 #ehg4 ,how this is put in practice in technical operations remains to be adverted to in the chapter on the privation of colour4 ,with regard to the communication of colour1 we have especially to bear in mind that animals and vegetables1 in a living state1 produce colours1 and hence their substances1 if deprived of colours1 can the more readily re-assume them4 #a ,verklrung1 literally clarification4 ,,xlvii4 ,,communication1 ,,apparent4 #ehh4 ,the communication of colours1 real as well as apparent1 corresponds1 as may easily be seen1 with their intermixture3 we need not1 therefore1 repeat what has been already sufficiently entered into4 #ehi4 ,yet we may here point out more circumstantially the importance of an apparent communication which takes place by means of reflection4 ,this phenomenon is well known1 but still it is pregnant with inferences1 and is of the greatest importance both to the investigator of nature and to the painter4 #eij4 ,let a surface coloured with any one of the positive colours be placed in the sun1 and let its reflection be thrown on other colourless objects4 ,this reflection is a kind of subdued light1 a half-light1 a half-shadow1 which1 in a subdued state1 reflects the colours in question4 #eia4 ,if this reflection acts on light surfaces1 it is so far overpowered that we can scarcely perceive the colour which accompanies it2 but if it acts on shadowed portions1 a sort of magical union takes place with the 4 ,shadow is the proper element of colour1 and in this case a subdued colour approaches it1 lighting up1 tinging1 and enlivening it4 ,and thus arises an appearance1 as powerful as agreeable1 which may render the most pleasing service to the painter who knows how to make use of it4 ,these are the types of the so-called reflexes1 which were only noticed late in the history of art1 and which have been too seldom employed in their full variety4 #eib4 ,the schoolmen called these colours colores notionales and intentionales1 and the history of the doctrine of colours will generally show that the old inquirers already observed the phenomena well enough1 and knew how to distinguish them properly1 although the whole method of treating such subjects is very different from ours4 ,,xlviii4 ,,extraction4 #eic4 ,colour may be extracted from substances1 whether they possess it naturally or by communication1 in various ways4 ,we have thus the power to remove it intentionally for a useful purpose1 but1 on the other hand1 it often flies contrary to our wish4 #eid4 ,not only are the elementary earths in their natural state white1 but vegetable and animal substances can be reduced to a white state without disturbing their texture4 ,a pure white is very desirable for various uses1 as in the instance of our preferring to use linen and cotton stuffs uncoloured4 ,in like manner some silk stuffs1 paper1 and other substances1 are the more agreeable the whiter they can be4 ,again1 the chief basis of all dyeing consists in white grounds4 ,for these reasons manufacturers1 aided by accident and contrivance1 have devoted themselves assiduously to discover means of extracting colour3 infinite experiments have been made in connexion with this object1 and many important facts have been arrived at4 #eie4 ,it is in accomplishing this entire extraction of colour that the operation of bleaching consists1 which is very generally practised empirically or methodically4 ,we will here shortly state the leading principles4 #eif4 ,light is considered as one of the first means of extracting colour from substances1 and not only the sun-light1 but the mere powerless day-light3 for as both lights--the direct light of the sun1 as well as the derived light of the sky--kindle ,bologna phosphorus1 so both act on coloured surfaces4 ,whether the light attacks the colour allied to it1 and1 as it were1 kindles and consumes it1 thus reducing the definite quality to a general state1 or whether some other operation1 unknown to us1 takes place1 it is clear that light exercises a great power on coloured surfaces1 and bleaches them more or less4 ,here1 however1 the different colours exhibit a different degree of durability2 yellow1 especially if prepared from certain materials1 is1 in this case1 the first to fly4 #eig4 ,not only light1 but air1 and especially water1 act strongly in destroying colour4 ,it has been even asserted that thread1 well soaked and spread on the grass at night1 bleaches better than that which is exposed1 after soaking1 to the sun-light4 ,thus1 in this case1 water proves to be a solving and conducting agent1 removing the accidental quality1 and restoring the substance to a general or colourless state4 #eih4 ,the extraction of colour is also effected by re-agents4 ,spirits of wine has a peculiar tendency to attract the juice which tinges plants1 and becomes coloured with it often in a very permanent manner4 ,sulphuric acid is very efficient in removing colour1 especially from wool and silk1 and every one is acquainted with the use of sulphur vapours in bleaching4 #eii4 ,the strongest acids have been recommended more recently as more expeditious agents in bleaching4 #fjj4 ,the alkaline re-agents produce the same effects by contrary means--lixiviums alone1 oils and fat combined with lixiviums to soap1 and so forth4 #fja4 ,before we dismiss this subject1 we observe ,pg #bdj that it may be well worth while to make certain delicate experiments as to how far light and air exhibit their action in the removal of colour4 ,it might be possible to expose coloured substances to the light under glass bells1 without air1 or filled with common or particular kinds of air4 ,the colours might be those of known fugacity1 and it might be observed whether any of the volatilized colour attached itself to the glass or was otherwise perceptible as a deposit or precipitate2 whether1 again1 in such a case1 this appearance would be perfectly like that which had gradually ceased to be visible1 or whether it had suffered any change4 ,skilful experimentalists might devise various contrivances with a view to such researches4 #fjb4 ,having thus first considered the operations of nature as subservient to our proposes1 we add a few observations on the modes in which they act against us4 #fjc4 ,the art of painting is so circumstanced that the most beautiful results of mind and labour are altered and destroyed in various ways by time4 ,hence great pains have been always taken to find durable pigments1 and so to unite them with each other and with their ground1 that their permanency might be further insured4 ,the technical history of the schools of painting affords sufficient information on this point4 #fjd4 ,we may here1 too1 mention a minor art1 to which1 in relation to dyeing1 we are much indebted1 namely1 the weaving of tapestry4 ,as the manufacturers were enabled to imitate the most delicate shades of pictures1 and hence often brought the most variously coloured materials together1 it was soon observed that the colours were not all equally durable1 but that some faded from the tapestry more quickly than others4 ,hence the most diligent efforts were made to ensure an equal permanency to all the colours and their gradations4 ,this object was especially promoted in ,france1 under ,colbert1 whose regulations to this effect constitute an epoch in the history of dyeing4 ,the gay dye which only aimed at a transient beauty1 was practised by a particular guild4 ,on the other hand1 great pains were taken to define the technical processes which promised durability4 ,and thus1 after considering the artificial extraction1 the evanescence1 and the perishable nature of brilliant appearances of colour1 we are again returned to the desideratum of permanency4 ,,xlix4 ,,nomenclature4 #fje4 ,after what has been adduced respecting the origin1 the increase1 and the affinity of colours1 we may be better enabled to judge what nomenclature would be desirable in future1 and what might be retained of that hitherto in use4 #fjf4 ,the nomenclature of colours1 like all other modes of designation1 but especially those employed to distinguish the objects of sense1 proceeded in the first instance from particular to general1 and from general back again to particular terms4 ,the name of the species became a generic name to which the individual was again referred4 #fjg4 ,this method might have been followed in consequence of the mutability and uncertainty of ancient modes of expression1 especially since1 in the early ages1 more reliance may be supposed to have been placed on the vivid impressions of sense4 ,the qualities of objects were described indistinctly1 because they were impressed clearly on every imagination4 #fjh4 ,the pure chromatic circle was limited1 it is true2 but1 specific as it was1 it appears to have been applied to innumerable objects1 while it was circumscribed by qualifying characteristics4 ,if we take a glance at the copiousness of the ,greek and ,roman terms1 we shall perceive how mutable the words were1 and how easily each was adapted to almost every point in the colorific circle4--,note ,w4 #fji4 ,in modern ages terms for many new gradations were introduced in consequence of the various operations of dyeing4 ,even the colours of fashion and their designations1 represented an endless series of specific hues4 ,we shall1 on occasion1 employ the chromatic terminology of modern languages1 whence it will appear that the aim has gradually been to introduce more exact definitions1 and to individualise and arrest a fixed and specific state by language equally distinct4 #faj4 ,with regard to the ,german terminology1 it has the advantage of possessing four monosyllabic names no longer to be traced to their origin1 viz41 yellow 7,gelb71 blue1 red1 green4 ,they represent the most general idea of colour to the imagination1 without reference to any very specific modification4 #faa4 ,if we were to add two other qualifying terms to each of these four1 as thus--red-yellow1 and yellow-red1 red-blue and blue-red1 yellow-green and green-yellow1 blue-green and green-blue1#a we should express the gradations of the chromatic circle with sufficient distinctness2 and if we were to add the designations of light and dark1 and again define1 in some measure1 the degree of purity or its opposite by the monosyllables black1 white1 grey1 brown1 we should have a tolerably sufficient range of expressions to describe the ordinary appearances presented to us1 without troubling ourselves whether they were produced dynamically or atomically4 #fab4 ,the specific and proper terms in use might1 however1 still be conveniently employed1 and we have thus made use of the words orange and violet4 ,we have in like manner employed the word purpur to designate a pure central red1 because the secretion of the murex or purpura is to be carried to the highest point of culmination by the action of the sun-light on fine linen saturated with the juice4 #a ,this description is suffered to remain because it accounts for the terminology employed throughout4--,t4 ,l4 ,,minerals4 #fac4 ,the colours of minerals are all of a chemical nature1 and thus the modes in which they are produced may be explained in a general way by what has been said on the subject of chemical colours4 #fad4 ,among the external characteristics of minerals1 the description of their colours occupies the first place2 and great pains have been taken1 in the spirit of modern times1 to define and arrest every such appearance exactly3 by this means1 however1 new difficulties1 it appears to us1 have been created1 which occasion no little inconvenience in practice4 #fae4 ,it is true1 this precision1 when we reflect how it arose1 carries with it its own excuse4 ,the painter has at all times been privileged in the use of colours4 ,the few specific hues1 in themselves1 admitted of no change2 but from these1 innumerable gradations were artificially produced which imitated the surface of natural objects4 ,it was1 therefore1 not to be wondered at that these gradations should also be adopted as criterions1 and that the artist should be invited to produce tinted patterns with which the objects of nature might be compared1 and according to which they were to receive their designations4 #faf4 ,but1 after all1 the terminology of colours which has been introduced in mineralogy1 is open to many objections4 ,the terms1 for instance1 have not been borrowed from the mineral kingdom1 as was possible enough in most cases1 but from all kinds of visible objects4 ,too many specific terms have been adopted2 and in seeking to establish new definitions by combining these1 the nomenclators have not reflected that they thus altogether efface the image from the imagination1 and the idea from the understanding4 ,lastly1 these individual designations of colours1 employed to a certain extent as elementary definitions1 are not arranged in the best manner as regards their respective derivation from each other3 hence1 the scholar must learn every single designation1 and impress an almost lifeless but positive language on his memory4 ,the further consideration of this would be too foreign to our present subject4#a #a ,these remarks have reference to the ,german mineralogical terminology4--,t4 ,,li4 ,,plants4 #fag4 ,the colours of organic bodies in general may be considered as a higher kind of chemical operation1 for which reason the ancients employed the word concoction1 1 to designate the process4 ,all the elementary colours1 as well as the combined and secondary hues1 appear on the surface of organic productions1 while on the other hand1 the interior1 if not colourless1 appears1 strictly speaking1 negative when brought to the light4 ,as we propose to communicate our views respecting organic nature1 to a certain extent1 in another place1 we only insert here what has been before connected with the doctrine of colours1 while it may serve as an introduction to the further consideration of the views alluded to3 and first1 of plants4 #fah4 ,seeds1 bulbs1 roots1 and what is generally shut out from the light1 or immediately surrounded by the earth1 appear1 for the most part1 white4 #fai4 ,plants reared from seed1 in darkness1 are white1 or approaching to yellow4 ,light1 on the other hand1 in acting on their colours1 acts at the same time on their form4 #fbj4 ,plants which grow in darkness make1 it is true1 long shoots from joint to joint3 but the stems between two joints are thus longer than they should be2 no side stems are produced1 and the metamorphosis of the plant does not take place4 #fba4 ,light1 on the other hand1 places it at once in an active state2 the plant appears green1 and the course of the metamorphosis proceeds uninterruptedly to the period of reproduction4 #fbb4 ,we know that the leaves of the stem are only preparations and pre-significations of the instruments of florification and fructification1 and accordingly we can already see colours in the leaves of the stem which1 as it were1 announce the flower from afar1 as is the case in the amaranthus4 #fbc4 ,there are white flowers whose petals have wrought or refined themselves to the greatest purity2 there are coloured ones1 in which the elementary hues may be said to fluctuate to and fro4 ,there are some which1 in tending to the higher state1 have only partially emancipated themselves from the green of the plant4 #fbd4 ,flowers of the same genus1 and even of the same kind1 are found of all colours4 ,roses1 and particularly mallows1 for example1 vary through a great portion of the colorific circle from white to yellow1 then through red-yellow to bright red1 and from thence to the darkest hue it can exhibit as it approaches blue4 #fbe4 ,others already begin from a higher degree in the scale1 as1 for example1 the poppy1 which is yellow-red in the first instance1 and which afterwards approaches a violet hue4 #fbf4 ,yet the same colours in species1 varieties1 and even in families and classes1 if not constant1 are still predominant1 especially the yellow colour3 blue is throughout rarer4 #fbg4 ,a process somewhat similar takes place in the juicy capsule of the fruit1 for it increases in colour from the green1 through the yellowish and yellow1 up to the highest red1 the colour of the rind thus indicating the degree of ripeness4 ,some are coloured all round1 some only on the sunny side1 in which last case the augmentation of the yellow into red1--the gradations crowding in and upon each other1--may be very well observed4 #fbh4 ,many fruits1 too1 are coloured internally2 pure red juices1 especially1 are common4 #fbi4 ,the colour which is found superficially in the flower and penetratingly in the fruit1 spreads itself through all the remaining parts1 colouring the roots and the juices of the stem1 and this with a very rich and powerful hue4 #fcj4 ,so1 again1 the colour of the wood passes from yellow through the different degrees of red up to pure red and on to brown4 ,blue woods are unknown to me2 and thus in this degree of organisation the active side exhibits itself powerfully1 although both principles appear balanced in the general green of the plant4 #fca4 ,we have seen above that the germ pushing from the earth is generally white and yellowish1 but that by means of the action of light and air it acquires a green colour4 ,the same happens with young leaves of trees1 as may be seen1 for example1 in the birch1 the young leaves of which are yellowish1 and if boiled1 yield a beautiful yellow juice3 afterwards they become greener1 while the leaves of other trees become gradually blue-green4 #fcb4 ,thus a yellow ingredient appears to belong more essentially to leaves than a blue one2 for this last vanishes in the autumn1 and the yellow of the leaf appears changed to a brown colour4 ,still more remarkable1 however1 are the particular cases where leaves in autumn again become pure yellow1 and others increase to the brightest red4 #fcc4 ,other plants1 again1 may1 by artificial treatment be entirely converted to a colouring matter1 which is as fine1 active1 and infinitely divisible as any other4 ,indigo and madder1 with which so much is effected1 are examples3 lichens are also used for dyes4 #fcd4 ,to this fact another stands immediately opposed2 we can1 namely1 extract the colouring part of plants1 and1 as it were1 exhibit it apart1 while the organisation does not on this account appear to suffer at all4 ,the colours of flowers may be extracted by spirits of wine1 and tinge it2 the petals meanwhile becoming white4 #fce4 ,there are various modes of acting on flowers and their juices by re-agents4 ,this has been done by ,boyle in many experiments4 ,roses are bleached by sulphur1 and may be restored to their first state by other acids2 roses are turned green by the smoke of tobacco4 ,,lii4 ,,worms1 ,,insects1 ,,fishes4 #fcf4 ,with regard to creatures belonging to the lower degrees of organisation1 we may first observe that worms1 which live in the earth and remain in darkness and cold moisture1 are imperfectly negatively coloured2 worms bred in warm moisture and darkness are colourless2 light seems expressly necessary to the definite exhibition of colour4 #fcg4 ,creatures which live in water1 which1 although a very dense medium1 suffers sufficient light to pass through it1 appear more or less coloured4 ,zoophytes1 which appear to animate the purest calcareous earth1 are mostly white2 yet we find corals deepened into the most beautiful yellow-red3 in other cells of worms this colour increases nearly to bright red4 #fch4 ,the shells of the crustaceous tribe are beautifully designed and coloured1 yet it is to be remarked that neither land-snails nor the shells of crustacea of fresh water1 are adorned with such bright colours as those of the sea4 #fci4 ,in examining shells1 particularly such as are spiral1 we find that a series of animal organs1 similar to each other1 must have moved increasingly forward1 and in turning on an axis produced the shell in a series of chambers1 divisions1 tubes1 and prominences1 according to a plan for ever growing larger4 ,we remark1 however1 that a tinging juice must have accompanied the development of these organs1 a juice which marked the surface of the shell1 probably through the immediate co-operation of the sea-water1 with coloured lines1 points1 spots1 and shadings3 this must have taken place at regular intervals1 and thus left the indications of increasing growth lastingly on the exterior2 meanwhile the interior is generally found white or only faintly coloured4 #fdj4 ,that such a juice is to be found in shell-fish is1 besides1 sufficiently proved by experience2 for the creatures furnish it in its liquid and colouring state3 the juice of the ink-fish is an example4 ,but a much stronger is exhibited in the red juice found in many shell-fish1 which was so famous in ancient times1 and has been employed with advantage by the moderns4 ,there is1 it appears1 in the entrails of many of the crustaceous tribe a certain vessel which is filled with a red juice2 this contains a very strong and durable colouring substance1 so much so that the entire creature may be crushed and boiled1 and yet out of this broth a sufficiently strong tinging liquid may be extracted4 ,but the little vessel filled with colour may be separated from the animal1 by which means of course a concentrated juice is gained4 #fda4 ,this juice has the property that when exposed to light and air it appears first yellowish1 then greenish2 it then passes to blue1 then to a violet1 gradually growing redder2 and lastly1 by the action of the sun1 and especially if transferred to cambric1 it assumes a pure bright red colour4 #fdb4 ,thus we should here have an augmentation1 even to culmination1 on the minus side1 which we cannot easily meet with in inorganic cases2 indeed1 we might almost call this example a passage through the whole scale1 and we are persuaded that by due experiments the entire revolution of the circle might really be effected1 for there is no doubt that by acids duly employed1 the pure red may be pushed beyond the culminating point towards scarlet4 #fdc4 ,this juice appears on the one hand to be connected with the phenomena of reproduction1 eggs being found1 the embryos of future shell-fish1 which contain a similar colouring principle4 ,on the other hand1 in animals ranking higher in the scale of being1 the secretion appears to bear some relation to the development of the blood4 ,the blood exhibits similar properties in regard to colour2 in its thinnest state it appears yellow2 thickened1 as it is found in the veins1 it appears red2 while the arterial blood exhibits a brighter red1 probably owing to the oxydation which takes place by means of breathing4 ,the venous blood approaches more to violet1 and by this mutability denotes the tendency to that augmentation and progression which are now familiar to us4 #fdd4 ,before we quit the element whence we derived the foregoing examples1 we may add a few observations on fishes1 whose scaly surface is coloured either altogether in stripes1 or in spots1 and still oftener exhibits a certain iridescent appearance1 indicating the affinity of the scales with the coats of shell-fish1 mother-of-pearl1 and even the pearl itself4 ,at the same time it should not be forgotten that warmer climates1 the influence of which extends to the watery regions1 produce1 embellish1 and enhance these colours in fishes in a still greater degree4 #fde4 ,in ,otaheite1 ,forster observed fishes with beautifully iridescent surfaces1 and this effect was especially apparent at the moment when the fish died4 ,we may here call to mind the hues of the chameleon1 and other similar appearances2 for when similar facts are presented together1 we are better enabled to trace them4 #fdf4 ,lastly1 although not strictly in the same class1 the iridescent appearance of certain mollusc may be mentioned1 as well as the phosphorescence which1 in some marine creatures1 it is said becomes iridescent just before it vanishes4 #fdg4 ,we now turn our attention to those creatures which belong to light1 air and dry warmth1 and it is here that we first find ourselves in the living region of colours4 ,here1 in exquisitely organised parts1 the elementary colours present themselves in their greatest purity and beauty4 ,they indicate1 however1 that the creatures they adorn1 are still low in the scale of organisation1 precisely because these colours can thus appear1 as it were1 unwrought4 ,here1 too1 heat seems to contribute much to their development4 #fdh4 ,we find insects which may be considered altogether as concentrated colouring matter2 among these1 the cochineals especially are celebrated2 with regard to these we observe that their mode of settling on vegetables1 and even nestling in them1 at the same time produces those excrescences which are so useful as mordants in fixing colours4 #fdi4 ,but the power of colour1 accompanied by regular organisation1 exhibits itself in the most striking manner in those insects which require a perfect metamorphosis for their development--in scarab1 and especially in butterflies4 #fej4 ,these last1 which might be called true productions of light and air1 often exhibit the most beautiful colours1 even in their chrysalis state1 indicating the future colours of the butterfly2 a consideration which1 if pursued further hereafter1 must undoubtedly afford a satisfactory insight into many a secret of organised being4 #fea4 ,if1 again1 we examine the wings of the butterfly more accurately1 and in its net-like web discover the rudiments of an arm1 and observe further the mode in which this1 as it were1 flattened arm is covered with tender plumage and constituted an organ of flying2 we believe we recognise a law according to which the great variety of tints is regulated4 ,this will be a subject for further investigation hereafter4 #feb4 ,that1 again1 heat generally has an influence on the size of the creature1 on the accomplishment of the form1 and on the greater beauty of the colours1 hardly needs to be remarked4 ,,liii4 ,,birds4 #fec4 ,the more we approach the higher organisations1 the more it becomes necessary to limit ourselves to a few passing observations2 for all the natural conditions of such organised beings are the result of so many premises1 that1 without having at least hinted at these1 our remarks would only appear daring1 and at the same time insufficient4 #fed4 ,we find in plants1 that the consummate flower and fruit are1 as it were1 rooted in the stem1 and that they are nourished by more perfect juices than the original roots first afforded2 we remark1 too1 that parasitical plants which derive their support from organised structures1 exhibit themselves especially endowed as to their energies and qualities4 ,we might in some sense compare the feathers of birds with plants of this description2 the feathers spring up as a last structural result from the surface of a body which has yet much in reserve for the completion of the external economy1 and thus are very richly endowed organs4 #fee4 ,the quills not only grow proportionally to a considerable size1 but are throughout branched1 by which means they properly become feathers1 and many of these feathered branches are again subdivided2 thus1 again1 recalling the structure of plants4 #fef4 ,the feathers are very different in shape and size1 but each still remains the same organ1 forming and transforming itself according to the constitution of the part of the body from which it springs4 #feg4 ,with the form1 the colour also becomes changed1 and a certain law regulates the general order of hues as well as that particular distribution by which a single feather becomes party coloured1 ,it is from this that all combination of variegated plumage arises1 and whence1 at last1 the eyes in the peacock's tail are produced4 ,it is a result similar to that which we have already unfolded in treating of the metamorphosis of plants1 and which we shall take an early opportunity to prove4 #feh4 ,although time and circumstances compel us here to pass by this organic law1 yet we are bound to refer to the chemical operations which commonly exhibit themselves in the tinting of feathers in a mode now sufficiently known to us4 #fei4 ,plumage is of all colours1 yet1 on the whole1 yellow deepening to red is commoner than blue4 #ffj4 ,the operation of light on the feathers and their colours1 is to be remarked in all cases4 ,thus1 for example1 the feathers on the breast of certain parrots1 are strictly yellow2 the scale-like anterior portion1 which is acted on by the light1 is deepened from yellow to red4 ,the breast of such a bird appears bright-red1 but if we blow into the feathers the yellow appears4 #ffa4 ,the exposed portion of the feathers is in all cases very different from that which1 in a quiet state1 is covered2 it is only the exposed portion1 for instance1 in ravens1 which exhibits the iridescent appearance2 the covered portion does not3 from which indication1 the feathers of the tail when ruffled together1 may be at once placed in the natural order again4 ,,liv4 ,,mammalia ,,and ,,human ,,beings4 #ffb4 ,here the elementary colours begin to leave us altogether4 ,we are arrived at the highest degree of the scale1 and shall not dwell on its characteristics long4 #ffc4 ,an animal of this class is distinguished among the examples of organised being4 ,every thing that exhibits itself about him is living4 ,of the internal structure we do not speak1 but confine ourselves briefly to the surface4 ,the hairs are already distinguished from feathers1 inasmuch as they belong more to the skin1 inasmuch as they are simple1 thread-like1 not branched4 ,they are however1 like feathers1 shorter1 longer1 softer1 and firmer1 colourless or coloured1 and all this in conformity to laws which might be defined4 #ffd4 ,white and black1 yellow1 yellow-red and brown1 alternate in various modifications1 but they never appear in such a state as to remind us of the elementary hues4 ,on the contrary1 they are all broken colours subdued by organic concoction1 and thus denote1 more or less1 the perfection of life in the being they belong to4 #ffe4 ,one of the most important considerations connected with morphology1 so far as it relates to surfaces1 is this1 that even in quadrupeds the spots of the skin have a relation with the parts underneath them4 ,capriciously as nature here appears1 on a hasty examination1 to operate1 she nevertheless consistently observes a secret law4 ,the development and application of this1 it is true1 are reserved only for accurate and careful investigation and sincere co-operation4 #fff4 ,if in some animals portions appear variegated with positive colours1 this of itself shows how far such creatures are removed from a perfect organisation2 for1 it may be said1 the nobler a creature is1 the more all the mere material of which he is composed1 is disguised by being wrought together2 the more essentially his surface corresponds with the internal organisation1 the less can it exhibit the elementary colours4 ,where all tends to make up a perfect whole1 any detached specific developments cannot take place4 #ffg4 ,of man we have little to say1 for he is entirely distinct from the general physiological results of which we now treat4 ,so much in this case is in affinity with the internal structure1 that the surface can only be sparingly endowed4 #ffh4 ,when we consider that brutes are rather encumbered than advantageously provided with intercutaneous muscles2 when we see that much that is superfluous tends to the surface1 as1 for instance1 large ears and tails1 as well as hair1 manes1 tufts2 we see that nature1 in such cases1 had much to give away and to lavish4 #ffi4 ,on the contrary1 the general surface of the human form is smooth and clean1 and thus in the most perfect examples1 the beautiful forms are apparent2 for it may be remarked in passing1 that a superfluity of hair on the chest1 arms1 and lower limbs1 rather indicates weakness than strength4 ,poets only have sometimes been induced1 probably by the example of the ferine nature1 so strong in other respects1 to extol similar attributes in their rough heroes4 #fgj4 ,but we have here chiefly to speak of colour1 and observe that the colour of the human skin1 in all its varieties1 is never an elementary colour1 but presents1 by means of organic concoction1 a highly complicated result4--,note ,x4 #fga4 ,that the colour of the skin and hair has relation with the differences of character1 is beyond question2 and we are led to conjecture that the circumstance of one or other organic system predominating1 produces the varieties we see4 ,a similar hypothesis may be applied to nations1 in which case it might perhaps be observed1 that certain colours correspond with certain confirmations1 which has always been observed of the negro physiognomy4 #fgb4 ,lastly1 we might here consider the problematical question1 whether all human forms and hues are not equally beautiful1 and whether custom and self-conceit are not the causes why one is preferred to another8 ,we venture1 however1 after what has been adduced1 to assert that the white man1 that is1 he whose surface varies from white to reddish1 yellowish1 brownish1 in short1 whose surface appears most neutral in hue and least inclines to any particular or positive colour1 is the most beautiful4 ,on the same principle a similar point of perfection in human conformation may be defined hereafter1 when the question relates to form4 ,we do not imagine that this long-disputed question is to be thus1 once for all1 settled1 for there are persons enough who have reason to leave this significancy of the exterior in doubt2 but we thus express a conclusion1 derived from observation and reflection1 such as might suggest itself to a mind aiming at a satisfactory decision4 ,we subjoin a few observations connected with the elementary chemical doctrine of colours4--,note ,y4 ,,lv4 ,,physical ,,and ,,chemical ,,effects ,,of ,,the ,,transmission ,,of ,,light ,,through ,,coloured ,,mediums4 #fgc4 ,the physical and chemical effects of colourless light are known1 so that it is unnecessary here to describe them at length4 ,colourless light exhibits itself under various conditions as exciting warmth1 as imparting a luminous quality to certain bodies1 as promoting oxydation and de-oxydation4 ,in the modes and degrees of these effects many varieties take place1 but no difference is found indicating a principle of contrast such as we find in the transmission of coloured light4 ,we proceed briefly to advert to this4 #fgd4 ,let the temperature of a dark room be observed by means of a very sensible air-thermometer2 if the bulb is then brought to the direct sun light as it shines into the room1 nothing is more natural than that the fluid should indicate a much higher degree of warmth4 ,if upon this we interpose coloured glasses1 it follows again quite naturally that the degree of warmth must be lowered2 first1 because the operation of the direct light is already somewhat impeded by the glass1 and again1 more especially1 because a coloured glass1 as a dark medium1 admits less light through it4 #fge4 ,but here a difference in the excitation of warmth exhibits itself to the attentive observer1 according to the colour of the glass4 ,the yellow and the yellow-red glasses produce a higher temperature than the blue and blue-red1 the difference being considerable4 #fgf4 ,this experiment may be made with the prismatic spectrum4 ,the temperature of the room being first remarked on the thermometer1 the blue coloured light is made to fall on the bulb1 when a somewhat higher degree of warmth is exhibited1 which still increases as the other colours are gradually brought to act on the mercury4 ,if the experiment is made with the water-prism1 so that the white light can be retained in the centre1 this1 refracted indeed1 but not yet coloured light1 is the warmest2 the other colours1 stand in relation to each other as before4 #fgg4 ,as we here merely describe1 without undertaking to deduce or explain this phenomenon1 we only remark in passing1 that the pure light is by no means abruptly and entirely at an end with the red division in the spectrum1 but that a refracted light is still to be observed deviating from its course and1 as it were1 insinuating itself beyond the prismatic image1 so that on closer examination it will hardly be found necessary to take refuge in invisible rays and their refraction4 #fgh4 ,the communication of light by means of coloured mediums exhibits the same difference4 ,the light communicates itself to ,bologna phosphorus through blue and violet glasses1 but by no means through yellow and yellow-red glasses4 ,it has been even remarked that the phosphori which have been rendered luminous under violet and blue glasses1 become sooner extinguished when afterwards placed under yellow and yellow-red glasses than those which have been suffered to remain in a dark room without any further influence4 #fgi4 ,these experiments1 like the foregoing1 may also be made by means of the prismatic spectrum1 when the same results take place4 #fhj4 ,to ascertain the effect of coloured light on oxydation and de-oxydation1 the following means may be employed3--,let moist1 perfectly white muriate of silver#a be spread on a strip of paper2 place it in the light1 so that it may become to a certain degree grey1 and then cut it in three portions4 ,of these1 one may be preserved in a book1 as a specimen of this state2 let another be placed under a yellow-red1 and the third under a blue-red glass4 ,the last will become a darker grey1 and exhibit a de-oxydation2 the other1 under the yellow-red glass1 will1 on the contrary1 become a lighter grey1 and thus approach nearer to the original state of more perfect oxydation4 ,the change in both may be ascertained by a comparison with the unaltered specimen4 #fha4 ,an excellent apparatus has been contrived to perform these experiments with the prismatic image4 ,the results are analogous to those already mentioned1 and we shall hereafter give the particulars1 making use of the labours of an accurate observer1 who has been for some time carefully prosecuting these experiments4#b #a ,now generally called chloride of silver3 the term in the original is ,hornsilber4--,t4 #b ,the individual alluded to was ,seebeck3 the result of his experiments was published in the second volume4--,t4 ,,lvi4 ,,chemical ,,effect ,,in ,,dioptrical ,,achromatism4 #fhb4 ,we first invite our readers to turn to what has been before observed on this subject 7#bhe1 #bih71 to avoid unnecessary repetition here4 #fhc4 ,we can thus give a glass the property of producing much wider coloured edges without refracting more strongly than before1 that is1 without displacing the object much more perceptibly4 #fhd4 ,this property is communicated to the glass by means of metallic oxydes4 ,minium1 melted and thoroughly united with a pure glass1 produces this effect1 and thus flint-glass 7#bia7 is prepared with oxyde of lead4 ,experiments of this kind have been carried farther1 and the so-called butter of antimony1 which1 according to a new preparation1 may be exhibited as a pure fluid1 has been made use of in hollow lenses and prisms1 producing a very strong appearance of colour with a very moderate refraction1 and presenting the effect which we have called hyperchromatism in a very vivid manner4 #fhe4 ,in common glass1 the alkaline nature obviously preponderates1 since it is chiefly composed of sand and alkaline salts2 hence a series of experiments1 exhibiting the relation of perfectly alkaline fluids to perfect acids1 might lead to useful results4 #fhf4 ,for1 could the maximum and minimum be found1 it would be a question whether a refracting medium could not be discovered1 in which the increasing and diminishing appearance of colour1 7an effect almost independent of refraction17 could not be done away with altogether1 while the displacement of the object would be unaltered4 #fhg4 ,how desirable1 therefore1 it would be with regard to this last point1 as well as for the elucidation of the whole of this third division of our work1 and1 indeed1 for the elucidation of the doctrine of colours generally1 that those who are occupied in chemical researches1 with new views ever opening to them1 should take this subject in hand1 pursuing into more delicate combinations what we have only roughly hinted at1 and prosecuting their inquiries with reference to science as a whole4 ,,part ,,iv4 ,,general ,,characteristics4 #fhh4 ,we have hitherto1 in a manner forcibly1 kept phenomena asunder1 which1 partly from their nature1 partly in accordance with our mental habits1 have1 as it were1 constantly sought to be reunited4 ,we have exhibited them in three divisions4 ,we have considered colours1 first1 as transient1 the result of an action and re-action in the eye itself2 next1 as passing effects of colourless1 light-transmitting1 transparent1 or opaque mediums on light2 especially on the luminous image2 lastly1 we arrived at the point where we could securely pronounce them as permanent1 and actually inherent in bodies4 #fhi4 ,in following this order we have as far as possible endeavoured to define1 to separate1 and to class the appearances4 ,but now that we need no longer be apprehensive of mixing or confounding them1 we may proceed1 first1 to state the general nature of these appearances considered abstractedly1 as an independent circle of facts1 and1 in the next place1 to show how this particular circle is connected with other classes of analogous phenomena in nature4 ,,the ,,facility ,,with ,,which ,,colour ,,appears4 #fij4 ,we have observed that colour under many conditions appears very easily4 ,the susceptibility of the eye with regard to light1 the constant re-action of the retina against it1 produce instantaneously a slight iridescence4 ,every subdued light may be considered as coloured1 nay1 we ought to call any light coloured1 inasmuch as it is seen4 ,colourless light1 colourless surfaces1 are1 in some sort1 abstract ideas2 in actual experience we can hardly be said to be aware of them4--,note ,z4 #fia4 ,if light impinges on a colourless body1 is reflected from it or passes through it1 colour immediately appears2 but it is necessary here to remember what has been so often urged by us1 namely1 that the leading conditions of refraction1 reflection1 c41 are not of themselves sufficient to produce the appearance4 ,sometimes1 it is true1 light acts with these merely as light1 but oftener as a defined1 circumscribed appearance1 as a luminous image4 ,the semi-opacity of the medium is often a necessary condition2 while half1 and double shadows1 are required for many coloured appearances4 ,in all cases1 however1 colour appears instantaneously4 ,we find1 again1 that by means of pressure1 breathing heat 7#dcb1 #dga71 by various kinds of motion and alteration on smooth clean surfaces 7#dfa71 as well as on colourless fluids 7#dgj71 colour is immediately produced4 #fib4 ,the slightest change has only to take place in the component parts of bodies1 whether by immixture with other particles or other such effects1 and colour either makes its appearance or becomes changed4 ,,the ,,force ,,of ,,colour4 #fic4 ,the physical colours1 and especially those of the prism1 were formerly called colores emphatici1 on account of their extraordinary beauty and force4 ,strictly speaking1 however1 a high degree of effect may be ascribed to all appearances of colour1 assuming that they are exhibited under the purest and most perfect conditions4 #fid4 ,the dark nature of colour1 its full rich quality1 is what produces the grave1 and at the same time fascinating impression we sometimes experience1 and as colour is to be considered a condition of light1 so it cannot dispense with light as the co-operating cause of its appearance1 as its basis or ground2 as a power thus displaying and manifesting colour4 ,,the ,,definite ,,nature ,,of ,,colour4 #fie4 ,the existence and the relatively definite character of colour are one and the same thing4 ,light displays itself and the face of nature1 as it were1 with a general indifference1 informing us as to surrounding objects perhaps devoid of interest or importance2 but colour is at all times specific1 characteristic1 significant4 #fif4 ,considered in a general point of view1 colour is determined towards one of two sides4 ,it thus presents a contrast which we call a polarity1 and which we may fitly designate by the expressions plus and minus4 ,plus4 ,minus4 ,yellow4 ,blue4 ,action4 ,negation4#a ,light4 ,shadow4 ,brightness4 ,darkness4 ,force4 ,weakness4 ,warmth4 ,coldness4 ,proximity4 ,distance4 ,repulsion ,attraction4 ,affinity with acids4 ,affinity with alkalis4 ,,combination ,,of ,,the ,,two ,,principles4 #fig4 ,if these specific1 contrasted principles are combined1 the respective qualities do not therefore destroy each other3 for if in this intermixture the ingredients are so perfectly balanced that neither is to be distinctly recognised1 the union again acquires a specific character2 it appears as a quality by itself in which we no longer think of combination4 ,this union we call green4 #fih4 ,thus1 if two opposite phenomena springing from the same source do not destroy each other when combined1 but in their union present a third appreciable and pleasing appearance1 this result at once indicates their harmonious relation4 ,the more perfect result yet remains to be adverted to4 ,,augmentation ,,to ,,red4 #fii4 ,blue and yellow do not admit of increased intensity without presently exhibiting a new appearance in addition to their own4 ,each colour1 in its lightest state1 is a dark2 if condensed it must become darker1 but this effect no sooner takes place than the hue assumes an appearance which we designate by the word reddish4 #gjj4 ,this appearance still increases1 so that when the highest degree of intensity is attained it predominates over the original hue4 ,a powerful impression of light leaves the sensation of red on the retina4 ,in the prismatic yellow-red which springs directly from the yellow1 we hardly recognise the yellow4 #gja4 ,this deepening takes place again by means of colourless semi-transparent mediums1 and here we see the effect in its utmost purity and extent4 ,transparent fluids1 coloured with any given hues1 in a series of glass-vessels1 exhibit it very strikingly4 ,the augmentation is unremittingly rapid and constant2 it is universal1 and obtains in physiological as well as in physical and chemical colours4 ,,junction ,,of ,,the ,,two ,,augmented ,,extremes4 #gjb4 ,as the extremes of the simple contrast produce a beautiful and agreeable appearance by their union1 so the deepened extremes on being united1 will present a still more fascinating colour2 indeed1 it might naturally be expected that we should here find the acme of the whole phenomenon4 ,,completeness ,,the ,,result ,,of ,,variety4 #gjc4 ,and such is the fact1 for pure red appears2 a colour to which1 from its excellence1 we have appropriated the term purpur4#b #gjd4 ,there are various modes in which pure red may appear4 ,by bringing together the violet edge and yellow-red border in prismatic experiments1 by continued augmentation in chemical operations1 and by the organic contrast in physiological effects4 #gje4 ,as a pigment it cannot be produced by intermixture or union1 but only by arresting the hue in substances chemically acted on1 at the high culminating point4 ,hence the painter is justified in assuming that there are three primitive colours from which he combines all the others4 ,the natural philosopher1 on the other hand1 assumes only two elementary colours1 from which he1 in like manner1 developes and combines the rest4 ,,completeness ,,the ,,result ,,of ,,variety ,,in ,,colour4 #gjf4 ,the various appearances of colour arrested in their different degrees1 and seen in juxtaposition1 produce a whole4 ,this totality is harmony to the eye4 #gjg4 ,the chromatic circle has been gradually presented to us2 the various relations of its progression are apparent to us4 ,two pure original principles in contrast1 are the foundation of the whole2 an augmentation manifests itself by means of which both approach a third state2 hence there exists on both sides a lowest and highest1 a simplest and most qualified state4 ,again1 two combinations present themselves2 first that of the simple primitive contrasts1 then that of the deepened contrasts4 ,,harmony ,,of ,,the ,,complete ,,state4 #gjh4 ,the whole ingredients of the chromatic scale1 seen in juxtaposition1 produce an harmonious impression on the eye4 ,the difference between the physical contrast and harmonious opposition in all its extent should not be overlooked4 ,the first resides in the pure restricted original dualism1 considered in its antagonizing elements2 the other results from the fully developed effects of the complete state4 #gji4 ,every single opposition in order to be harmonious must comprehend the whole4 ,the physiological experiments are sufficiently convincing on this point4 ,a development of all the possible contrasts of the chromatic scale will be shortly given4#c ,,facility ,,with ,,which ,,colour ,,may ,,be ,,made ,,to ,,tend ,,either ,,to ,,the ,,plus ,,or ,,minus ,,side4 #gaj4 ,we have already had occasion to take notice of the mutability of colour in considering its so-called augmentation and progressive variations round the whole circle2 but the hues even pass and repass from one side to the other1 rapidly and of necessity4 #gaa4 ,physiological colours are different in appearance as they happen to fall on a dark or on a light ground4 ,in physical colours the combination of the objective and subjective experiments is very remarkable4 ,the epoptical colours1 it appears1 are contrasted according as the light shines through or upon them4 ,to what extent the chemical colours may be changed by fire and alkalis1 has been sufficiently shown in its proper place4 ,,evanescence ,,of ,,colour4 #gab4 ,all that has been adverted to as subsequent to the rapid excitation and definition of colour1 immixture1 augmentation1 combination1 separation1 not forgetting the law of compensatory harmony1 all takes place with the greatest rapidity and facility2 but with equal quickness colour again altogether disappears4 #gac4 ,the physiological appearances are in no wise to be arrested2 the physical last only as long as the external condition lasts2 even the chemical colours have great mutability1 they may be made to pass and repass from one side to the other by means of opposite re-agents1 and may even be annihilated altogether4 ,,permanence ,,of ,,colour4 #gad4 ,the chemical colours afford evidence of very great duration4 ,colours fixed in glass by fusion1 and by nature in gems1 defy all time and re-action4 #gae4 ,the art of dyeing again fixes colour very powerfully4 ,the hues of pigments which might otherwise be easily rendered mutable by re-agents1 may be communicated to substances in the greatest permanency by means of mordants4 #a ,wirkung1 ,beraubung2 the last would be more literally rendered privation4 ,the author has already frequently made use of the terms active and passive as equivalent to plus and minus4--,t4 #b ,wherever this word occurs incidentally it is translated pure red1 the ,english word purple being generally employed to denote a colour similar to violet4--,t4 #c ,no diagram or table of this kind was ever given by the author4--,t4 ,,part ,v4 ,,relation ,,to ,,other ,,pursuits--,,relation ,,to ,,philosophy4 #gaf4 ,the investigator of nature cannot be required to be a philosopher1 but it is expected that he should so far have attained the habit of philosophizing1 as to distinguish himself essentially from the world1 in order to associate himself with it again in a higher sense4 ,he should form to himself a method in accordance with observation1 but he should take heed not to reduce observation to mere notion1 to substitute words for this notion1 and to use and deal with these words as if they were things4 ,he should be acquainted with the labours of philosophers1 in order to follow up the phenomena which have been the subject of his observation1 into the philosophic region4 #gag4 ,it cannot be required that the philosopher should be a naturalist1 and yet his co-operation in physical researches is as necessary as it is desirable4 ,he needs not an acquaintance with details for this1 but only a clear view of those conclusions where insulated facts meet4 #gah4 ,we have before 7#age7 alluded to this important consideration1 and repeat it here where it is in its place4 ,the worst that can happen to physical science as well as to many other kinds of knowledge is1 that men should treat a secondary phenomenon as a primordial one1 and 7since it is impossible to derive the original fact from the secondary state71 seek to explain what is in reality the cause by an effect made to usurp its place4 ,hence arises an endless confusion1 a mere verbiage1 a constant endeavour to seek and to find subterfuges whenever truth presents itself and threatens to be overpowering4 #gai4 ,while the observer1 the investigator of nature1 is thus dissatisfied in finding that the appearances he sees still contradict a received theory1 the philosopher can calmly continue to operate in his abstract department on a false result1 for no result is so false but that it can be made to appear valid1 as form without substance1 by some means or other4 #gbj4 ,if1 on the other hand1 the investigator of nature can attain to the knowledge of that which we have called a primordial phenomenon1 he is safe2 and the philosopher with him4 ,the investigator of nature is safe1 since he is persuaded that he has here arrived at the limits of his science1 that he finds himself at the height of experimental research2 a height whence he can look back upon the details of observation in all its steps1 and forwards into1 if he cannot enter1 the regions of theory4 ,the philosopher is safe1 for he receives from the experimentalist an ultimate fact1 which1 in his hands1 now becomes an elementary one4 ,he now justly pays little attention to appearances which are understood to be secondary1 whether he already finds them scientifically arranged1 or whether they present themselves to his casual observation scattered and confused4 ,should he even be inclined to go over this experimental ground himself1 and not be averse to examination in detail1 he does this conveniently1 instead of lingering too long in the consideration of secondary and intermediate circumstances1 or hastily passing them over without becoming accurately acquainted with them4 #gba4 ,to place the doctrine of colours nearer1 in this sense1 within the philosopher's reach1 was the author's wish2 and although the execution of his purpose1 from various causes1 does not correspond with his intention1 he will still keep this object in view in an intended recapitulation1 as well as in the polemical and historical portions of his work2 for he will have to return to the consideration of this point hereafter1 on an occasion where it will be necessary to speak with less reserve4 ,,relation ,,to ,,mathematics4 #gbb4 ,it may be expected that the investigator of nature1 who proposes to treat the science of natural philosophy in its entire range1 should be a mathematician4 ,in the middle ages1 mathematics was the chief organ by means of which men hoped to master the secrets of nature1 and even now1 geometry in certain departments of physics1 is justly considered of first importance4 #gbc4 ,the author can boast of no attainments of this kind1 and on this account confines himself to departments of science which are independent of geometry2 departments which in modern times have been opened up far and wide4 #gbd4 ,it will be universally allowed that mathematics1 one of the noblest auxiliaries which can be employed by man1 has1 in one point of view1 been of the greatest use to the physical sciences2 but that1 by a false application of its methods1 it has1 in many respects1 been prejudicial to them1 is also not to be denied2 we find it here and there reluctantly admitted4 #gbe4 ,the theory of colours1 in particular1 has suffered much1 and its progress has been incalculably retarded by having been mixed up with optics generally1 a science which cannot dispense with mathematics2 whereas the theory of colours1 in strictness1 may be investigated quite independently of optics4 #gbf4 ,but besides this there was an additional evil4 ,a great mathematician was possessed with an entirely false notion on the physical origin of colours2 yet1 owing to his great authority as a geometer1 the mistakes which he committed as an experimentalist long became sanctioned in the eyes of a world ever fettered in prejudices4 #gbg4 ,the author of the present inquiry has endeavoured throughout to keep the theory of colours distinct from the mathematics1 although there are evidently certain points where the assistance of geometry would be desirable4 ,had not the unprejudiced mathematicians1 with whom he has had1 or still has1 the good fortune to be acquainted1 been prevented by other occupations from making common cause with him1 his work would not have wanted some merit in this respect4 ,but this very want may be in the end advantageous1 since it may now become the object of the enlightened mathematician to ascertain where the doctrine of colours is in need of his aid1 and how he can contribute the means at his command with a view to the complete elucidation of this branch of physics4 #gbh4 ,in general it were to be wished that the ,germans1 who render such good service to science1 while they adopt all that is good from other nations1 could by degrees accustom themselves to work in concert4 ,we live1 it must be confessed1 in an age1 the habits of which are directly opposed to such a wish4 ,every one seeks1 not only to be original in his views1 but to be independent of the labours of others1 or at least to persuade himself that he is so1 even in the course of his life and occupation4 ,it is very often remarked that men who undoubtedly have accomplished much1 quote themselves only1 their own writings1 journals1 and compendiums2 whereas it would be far more advantageous for the individual1 and for the world1 if many were devoted to a common pursuit4 ,the conduct of our neighbours the ,french is1 in this respect1 worthy of imitation2 we have a pleasing instance in ,cuvier's preface to his ,tableau lmentaire de l',histoire ,naturelle des ,animaux4 #gbi4 ,he who has observed science and its progress with an unprejudiced eye1 might even ask whether it is desirable that so many occupations and aims1 though allied to each other1 should be united in one person1 and whether it would not be more suitable for the limited powers of the human mind to distinguish1 for example1 the investigator and inventor1 from him who employs and applies the result of experiment8 ,astronomers1 who devote themselves to the observation of the heavens and the discovery or enumeration of stars1 have in modern times formed1 to a certain extent1 a distinct class from those who calculate the orbits1 consider the universe in its connexion1 and more accurately define its laws4 ,the history of the doctrine of colours will often lead us back to these considerations4 ,,relation ,,to ,,the ,,technical ,,operations ,,of ,,the ,,dyer4 #gcj4 ,if in our labours we have gone out of the province of the mathematician1 we have1 on the other hand1 endeavoured to meet the practical views of the dyer2 and although the chapter which treats of colour in a chemical point of view is not the most complete and circumstantial1 yet in that portion1 as well as in our general observations respecting colour1 the dyer will find his views assisted far more than by the theory hitherto in vogue1 which failed to afford him any assistance4 #gca4 ,it is curious1 in this view1 to take a glance at the works containing directions on the art of dyeing4 ,as the ,catholic1 on entering his temple1 sprinkles himself with holy water1 and after bending the knee1 proceeds perhaps to converse with his friends on his affairs1 without any especial devotion2 so all the treatises on dyeing begin with a respectful allusion to the accredited theory1 without afterwards exhibiting a single trace of any principle deduced from this theory1 or showing that it has thrown light on any part of the art1 or that it offers any useful hints in furtherance of practical methods4 #gcb4 ,on the other hand1 there are men who1 after having become thoroughly and experimentally acquainted with the nature of dyes1 have not been able to reconcile their observations with the received theory2 who have1 in short1 discovered its weak points1 and sought for a general view more consonant to nature and experience4 ,when we come to the names of ,castel and ,glich1 in our historical review1 we shall have occasion to enter into this more fully1 and an opportunity will then present itself to show that an assiduous experience in taking advantage of every accident may1 in fact1 be said almost to exhaust the knowledge of the province to which it is confined4 ,the high and complete result is then submitted to the theorist1 who1 if he examines facts with accuracy1 and reasons with candour1 will find such materials eminently useful as a basis for his conclusions4--,note ,a ,a4 ,,relation ,,to ,,physiology ,,and ,,pathology4 #gcc4 ,if the phenomena adduced in the chapter where colours were considered in a physiological and pathological view are for the most part generally known1 still some new views1 mixed up with them1 will not be unacceptable to the physiologist4 ,we especially hope to have given him cause to be satisfied by classing certain phenomena which stood alone1 under analogous facts1 and thus1 in some measure1 to have prepared the way for his further investigations4 #gcd4 ,the appendix on pathological colours1 again1 is admitted to be scanty and unconnected4 ,we reflect1 however1 that ,germany can boast of men who are not only highly experienced in this department1 but are likewise so distinguished for general cultivation1 that it can cost them but little to revise this portion1 to complete what has been sketched1 and at the same time to connect it with the higher facts of organisation4 ,,relation ,,to ,,natural ,,history4 #gce4 ,if we may at all hope that natural history will gradually be modified by the principle of deducing the ordinary appearances of nature from higher phenomena1 the author believes he may have given some hints and introductory views bearing on this object also4 ,as colour1 in its infinite variety1 exhibits itself on the surface of living beings1 it becomes an important part of the outward indications1 by means of which we can discover what passes underneath4 #gcf4 ,in one point of view it is certainly not to be too much relied on1 on account of its indefinite and mutable nature2 yet even this mutability1 inasmuch as it exhibits itself as a constant quality1 again becomes a criterion of a mutable vitality2 and the author wishes nothing more than that time may be granted him to develop the results of his observations on this subject more fully2 here they would not be in their place4 ,,relation ,,to ,,general ,,physics4 #gcg4 ,the state in which general physics now is1 appears1 again1 particularly favourable to our labours2 for natural philosophy1 owing to indefatigable and variously directed research1 has gradually attained such eminence1 that it appears not impossible to refer a boundless empiricism to one centre4 #gch4 ,without referring to subjects which are too far removed from our own province1 we observe that the formul under which the elementary appearances of nature are expressed1 altogether tend in this direction2 and it is easy to see that through this correspondence of expression1 a correspondence in meaning will necessarily be soon arrived at4 #gci4 ,true observers of nature1 however they may differ in opinion in other respects1 will agree that all which presents itself as appearance1 all that we meet with as phenomenon1 must either indicate an original division which is capable of union1 or an original unity which admits of division1 and that the phenomenon will present itself accordingly4 ,to divide the united1 to unite the divided1 is the life of nature2 this is the eternal systole and diastole1 the eternal collapsion and expansion1 the inspiration and expiration of the world in which we live and move4 #gdj4 ,it is hardly necessary to observe that what we here express as number and restrict to dualism is to be understood in a higher sense2 the appearance of a third1 a fourth order of facts progressively developing themselves is to be similarly understood2 but actual observation should1 above all1 be the basis of all these expressions4 #gda4 ,iron is known to us as a peculiar substance1 different from other substances3 in its ordinary state we look upon it as a mere material remarkable only on account of its fitness for various uses and applications4 ,how little1 however1 is necessary to do away with the comparative insignificancy of this substance4 ,a two-fold power is called forth1#a which1 while it tends again to a state of union1 and1 as it were1 seeks itself1 acquires a kind of magical relation with its like1 and propagates this double property1 which is in fact but a principle of reunion1 throughout all bodies of the same kind4 ,we here first observe the mere substance1 iron2 we see the division that takes place in it propagate itself and disappear1 and again easily become re-excited4 ,this1 according to our mode of thinking1 is a primordial phenomenon in immediate relation with its idea1 and which acknowledges nothing earthly beyond it4 #gdb4 ,electricity is again peculiarly characterised4 ,as a mere quality we are unacquainted with it2 for us it is a nothing1 a zero1 a mere point1 which1 however1 dwells in all apparent existences1 and at the same time is the point of origin whence1 on the slightest stimulus1 a double appearance presents itself1 an appearance which only manifests itself to vanish4 ,the conditions under which this manifestation is excited are infinitely varied1 according to the nature of particular bodies4 ,from the rudest mechanical friction of very different substances with one another1 to the mere contiguity of two entirely similar bodies1 the phenomenon is present and stirring1 nay1 striking and powerful1 and so decided and specific1 that when we employ the terms or formul polarity1 plus and minus1 for north and south1 for glass and resin1 we do so justifiably and in conformity with nature4 #gdc4 ,this phenomenon1 although it especially affects the surface1 is yet by no means superficial4 ,it influences the tendency or determination of material qualities1 and connects itself in immediate co-operation with the important double phenomenon which takes place so universally in chemistry1--oxydation1 and de-oxydation4 #gdd4 ,to introduce and include the appearances of colour in this series1 this circle of phenomena was the object of our labours4 ,what we have not succeeded in others will accomplish4 ,we found a primordial vast contrast between light and darkness1 which may be more generally expressed by light and its absence4 ,we looked for the intermediate state1 and sought by means of it to compose the visible world of light1 shade1 and colour4 ,in the prosecution of this we employed various terms applicable to the development of the phenomena1 terms which we adopted from the theories of magnetism1 of electricity1 and of chemistry4 ,it was necessary1 however1 to extend this terminology1 since we found ourselves in an abstract region1 and had to express more complicated relations4 #gde4 ,if electricity and galvanism1 in their general character1 are distinguished as superior to the more limited exhibition of magnetic phenomena1 it may be said that colour1 although coming under similar laws1 is still superior2 for since it addresses itself to the noble sense of vision1 its perfections are more generally displayed4 ,compare the varied effects which result from the augmentation of yellow and blue to red1 from the combination of these two higher extremes to pure red1 and the union of the two inferior extremes to green4 ,what a far more varied scheme is apparent here than that in which magnetism and electricity are comprehended4 ,these last phenomena may be said to be inferior again on another account2 for though they penetrate and give life to the universe1 they cannot address themselves to man in a higher sense in order to his employing them sthetically4 ,the general1 simple1 physical law must first be elevated and diversified itself in order to be available for elevated uses4 #gdf4 ,if the reader1 in this spirit1 recalls what has been stated by us throughout1 generally and in detail1 with regard to colour1 he will himself pursue and unfold what has been here only lightly hinted at4 ,he will augur well for science1 technical processes1 and art1 if it should prove possible to rescue the attractive subject of the doctrine of colours from the atomic restriction and isolation in which it has been banished1 in order to restore it to the general dynamic flow of life and action which the present age loves to recognise in nature4 ,these considerations will press upon us more strongly when1 in the historical portion1 we shall have to speak of many an enterprising and intelligent man who failed to possess his contemporaries with his convictions4 ,,relation ,,to ,,the ,,theory ,,of ,,music4 #gdg4 ,before we proceed to the moral associations of colour1 and the sthetic influences arising from them1 we have here to say a few words on its relation to melody4 ,that a certain relation exists between the two1 has been always felt2 this is proved by the frequent comparisons we meet with1 sometimes as passing allusions1 sometimes as circumstantial parallels4 ,the error which writers have fallen into in trying to establish this analogy we would thus define3 #gdh4 ,colour and sound do not admit of being directly compared together in any way1 but both are referable to a higher formula1 both are derivable1 although each for itself1 from this higher law4 ,they are like two rivers which have their source in one and the same mountain1 but subsequently pursue their way under totally different conditions in two totally different regions1 so that throughout the whole course of both no two points can be compared4 ,both are general1 elementary effects acting according to the general law of separation and tendency to union1 of undulation and oscillation1 yet acting thus in wholly different provinces1 in different modes1 on different elementary mediums1 for different senses4--,note ,b ,b4 #gdi4 ,could some investigator rightly adopt the method in which we have connected the doctrine of colours with natural philosophy generally1 and happily supply what has escaped or been missed by us1 the theory of sound1 we are persuaded1 might be perfectly connected with general physics3 at present it stands1 as it were1 isolated within the circle of science4 #gej4 ,it is true it would be an undertaking of the greatest difficulty to do away with the positive character which we are now accustomed to attribute to music--a character resulting from the achievements of practical skill1 from accidental1 mathematical1 sthetical influences--and to substitute for all this a merely physical inquiry tending to resolve the science into its first elements4 ,yet considering the point at which science and art are now arrived1 considering the many excellent preparatory investigations that have been made relative to this subject1 we may perhaps still see it accomplished4 ,,concluding ,,observations ,,on ,,terminology4 #gea4 ,we never sufficiently reflect that a language1 strictly speaking1 can only be symbolical and figurative1 that it can never express things directly1 but only1 as it were1 reflectedly4 ,this is especially the case in speaking of qualities which are only imperfectly presented to observation1 which might rather be called powers than objects1 and which are ever in movement throughout nature4 ,they are not to be arrested1 and yet we find it necessary to describe them2 hence we look for all kinds of formul in order1 figuratively at least1 to define them4 #geb4 ,metaphysical formul have breadth as well as depth1 but on this very account they require a corresponding import2 the danger here is vagueness4 ,mathematical expressions may in many cases be very conveniently and happily employed1 but there is always an inflexibility in them1 and we presently feel their inadequacy2 for even in elementary cases we are very soon conscious of an incommensurable idea2 they are1 besides1 only intelligible to those who are especially conversant in the sciences to which such formul are appropriated4 ,the terms of the science of mechanics are more addressed to the ordinary mind1 but they are ordinary in other senses1 and always have something unpolished2 they destroy the inward life to offer from without an insufficient substitute for it4 ,the formul of the corpuscular theories are nearly allied to the last2 through them the mutable becomes rigid1 description and expression uncouth3 while1 again1 moral terms1 which undoubtedly can express nicer relations1 have the effect of mere symbols in the end1 and are in danger of being lost in a play of wit4 #gec4 ,if1 however1 a writer could use all these modes of description and expression with perfect command1 and thus give forth the result of his observations on the phenomena of nature in a diversified language2 if he could preserve himself from predilections1 still embodying a lively meaning in as animated an expression1 we might look for much instruction communicated in the most agreeable of forms4 #ged4 ,yet1 how difficult it is to avoid substituting the sign for the thing2 how difficult to keep the essential quality still living before us1 and not to kill it with the word4 ,with all this1 we are exposed in modern times to a still greater danger by adopting expressions and terminologies from all branches of knowledge and science to embody our views of simple nature4 ,astronomy1 cosmology1 geology1 natural history1 nay religion and mysticism1 are called in in aid2 and how often do we not find a general idea and an elementary state rather hidden and obscured than elucidated and brought nearer to us by the employment of terms1 the application of which is strictly specific and secondary4 ,we are quite aware of the necessity which led to the introduction and general adoption of such a language1 we also know that it has become in a certain sense indispensable2 but it is only a moderate1 unpretending recourse to it1 with an internal conviction of its fitness1 that can recommend it4 #gee4 ,after all1 the most desirable principle would be that writers should borrow the expressions employed to describe the details of a given province of investigation from the province itself2 treating the simplest phenomenon as an elementary formula1 and deriving and developing the more complicated designations from this4 #gef4 ,the necessity and suitableness of such a conventional language where the elementary sign expresses the appearance itself1 has been duly appreciated by extending1 for instance1 the application of the term polarity1 which is borrowed from the magnet to electricity1 c4 ,the plus and minus which may be substituted for this1 have found as suitable an application to many phenomena2 even the musician1 probably without troubling himself about these other departments1 has been naturally led to express the leading difference in the modes of melody by major and minor4 #geg4 ,for ourselves we have long wished to introduce the term polarity into the doctrine of colours2 with what right and in what sense1 the present work may show4 ,perhaps we may hereafter find room to connect the elementary phenomena together according to our mode1 by a similar use of symbolical terms1 terms which must at all times convey the directly corresponding idea2 we shall thus render more explicit what has been here only alluded to generally1 and perhaps too vaguely expressed4 #a ,eine ,entzweyung geht vor2 literally1 a division takes place4 ,according to some1 the two magnetic powers are previously in the bar1 and are then separated at the ends4--,t4 ,,part ,,vi4 ,,effect ,,of ,,colour ,,with ,,reference ,,to ,,moral ,,associations4 #geh4 ,since colour occupies so important a place in the series of elementary phenomena1 filling as it does the limited circle assigned to it with fullest variety1 we shall not be surprised to find that its effects are at all times decided and significant1 and that they are immediately associated with the emotions of the mind4 ,we shall not be surprised to find that these appearances presented singly1 are specific1 that in combination they may produce an harmonious1 characteristic1 often even an inharmonious effect on the eye1 by means of which they act on the mind2 producing this impression in their most general elementary character1 without relation to the nature or form of the object on whose surface they are apparent4 ,hence1 colour considered as an element of art1 may be made subservient to the highest sthetical ends4--,note ,c ,c4 #gei4 ,people experience a great delight in colour1 generally4 ,the eye requires it as much as it requires light4 ,we have only to remember the refreshing sensation we experience1 if on a cloudy day the sun illumines a single portion of the scene before us and displays its colours4 ,that healing powers were ascribed to coloured gems1 may have arisen from the experience of this indefinable pleasure4 #gfj4 ,the colours which we see on objects are not qualities entirely strange to the eye2 the organ is not thus merely habituated to the impression2 no1 it is always predisposed to produce colour of itself1 and experiences a sensation of delight if something analogous to its own nature is offered to it from without2 if its susceptibility is distinctly determined towards a given state4 #gfa4 ,from some of our earlier observations we can conclude1 that general impressions produced by single colours cannot be changed1 that they act specifically1 and must produce definite1 specific states in the living organ4 #gfb4 ,they likewise produce a corresponding influence on the mind4 ,experience teaches us that particular colours excite particular states of feeling4 ,it is related of a witty ,frenchman1 ,il prtendoit que son ton de conversation avec ,madame toit chang depuis qu'elle avoit chang en cramoisi le meuble de son cabinet1 qui toit bleu4 #gfc4 ,in order to experience these influences completely1 the eye should be entirely surrounded with one colour2 we should be in a room of one colour1 or look through a coloured glass4 ,we are then identified with the hue1 it attunes the eye and mind in mere unison with itself4 #gfd4 ,the colours on the plus side are yellow1 red-yellow 7orange71 yellow-red 7minium1 cinnabar74 ,the feelings they excite are quick1 lively1 aspiring4 ,,yellow4 #gfe4 ,this is the colour nearest the light4 ,it appears on the slightest mitigation of light1 whether by semi-transparent mediums or faint reflection from white surfaces4 ,in prismatic experiments it extends itself alone and widely in the light space1 and while the two poles remain separated from each other1 before it mixes with blue to produce green it is to be seen in its utmost purity and beauty4 ,how the chemical yellow developes itself in and upon the white1 has been circumstantially described in its proper place4 #gff4 ,in its highest purity it always carries with it the nature of brightness1 and has a serene1 gay1 softly exciting character4 #gfg4 ,in this state1 applied to dress1 hangings1 carpeting1 c41 it is agreeable4 ,gold in its perfectly unmixed state1 especially when the effect of polish is superadded1 gives us a new and high idea of this colour2 in like manner1 a strong yellow1 as it appears on satin1 has a magnificent and noble effect4 #gfh4 ,we find from experience1 again1 that yellow excites a warm and agreeable impression4 ,hence in painting it belongs to the illumined and emphatic side4 #gfi4 ,this impression of warmth may be experienced in a very lively manner if we look at a landscape through a yellow glass1 particularly on a grey winter's day4 ,the eye is gladdened1 the heart expanded and cheered1 a glow seems at once to breathe towards us4 #ggj4 ,if1 however1 this colour in its pure and bright state is agreeable and gladdening1 and in its utmost power is serene and noble1 it is1 on the other hand1 extremely liable to contamination1 and produces a very disagreeable effect if it is sullied1 or in some degree tends to the minus side4 ,thus1 the colour of sulphur1 which inclines to green1 has a something unpleasant in it4 #gga4 ,when a yellow colour is communicated to dull and coarse surfaces1 such as common cloth1 felt1 or the like1 on which it does not appear with full energy1 the disagreeable effect alluded to is apparent4 ,by a slight and scarcely perceptible change1 the beautiful impression of fire and gold is transformed into one not undeserving the epithet foul2 and the colour of honour and joy reversed to that of ignominy and aversion4 ,to this impression the yellow hats of bankrupts and the yellow circles on the mantles of ,jews1 may have owed their origin4 ,,red-,,yellow4 #ggb4 ,as no colour can be considered as stationary1 so we can very easily augment yellow into reddish by condensing or darkening it4 ,the colour increases in energy1 and appears in red-yellow more powerful and splendid4 #ggc4 ,all that we have said of yellow is applicable here in a higher degree4 ,the red-yellow gives an impression of warmth and gladness1 since it represents the hue of the intenser glow of fire1 and of the milder radiance of the setting sun4 ,hence it is agreeable around us1 and again1 as clothing1 in greater or less degrees is cheerful and magnificent4 ,a slight tendency to red immediately gives a new character to yellow1 and while the ,english and ,germans content themselves with bright pale yellow colours in leather1 the ,french1 as ,castel has remarked1 prefer a yellow enhanced to red2 indeed1 in general1 everything in colour is agreeable to them which belongs to the active side4 ,,yellow-,,red4 #ggd4 ,as pure yellow passes very easily to red-yellow1 so the deepening of this last to yellow-red is not to be arrested4 ,the agreeable1 cheerful sensation which red-yellow excites1 increases to an intolerably powerful impression in bright yellow-red4 #gge1 ,the active side is here in its highest energy1 and it is not to be wondered at that impetuous1 robust1 uneducated men1 should be especially pleased with this colour4 ,among savage nations the inclination for it has been universally remarked1 and when children1 left to themselves1 begin to use tints1 they never spare vermilion and minium4 #ggf4 ,in looking steadfastly at a perfectly yellow-red surface1 the colour seems actually to penetrate the organ4 ,it produces an extreme excitement1 and still acts thus when somewhat darkened4 ,a yellow-red cloth disturbs and enrages animals4 ,i have known men of education to whom its effect was intolerable if they chanced to see a person dressed in a scarlet cloak on a grey1 cloudy day4 #ggg4 ,the colours on the minus side are blue1 red-blue1 and blue-red4 ,they produce a restless1 susceptible1 anxious impression4 ,,blue4 #ggh4 ,as yellow is always accompanied with light1 so it may be said that blue still brings a principle of darkness with it4 #ggi4 ,this colour has a peculiar and almost indescribable effect on the eye4 ,as a hue it is powerful1 but it is on the negative side1 and in its highest purity is1 as it were1 a stimulating negation4 ,its appearance1 then1 is a kind of contradiction between excitement and repose4 #ghj4 ,as the upper sky and distant mountains appear blue1 so a blue surface seems to retire from us4 #gha4 ,but as we readily follow an agreeable object that flies from us1 so we love to contemplate blue1 not because it advances to us1 but because it draws us after it4 #ghb4 ,blue gives us an impression of cold1 and thus1 again1 reminds us of shade4 ,we have before spoken of its affinity with black4 #ghc4 ,rooms which are hung with pure blue1 appear in some degree larger1 but at the same time empty and cold4 #ghd4 ,the appearance of objects seen through a blue glass is gloomy and melancholy4 #ghe4 ,when blue partakes in some degree of the plus side1 the effect is not disagreeable4 ,sea-green is rather a pleasing colour4 ,,red-,,blue4 #ghf4 ,we found yellow very soon tending to the intense state1 and we observe the same progression in blue4 #ghg4 ,blue deepens very mildly into red1 and thus acquires a somewhat active character1 although it is on the passive side4 ,its exciting power is1 however1 of a very different kind from that of the red-yellow4 ,it may be said to disturb rather than enliven4 #ghh4 ,as augmentation itself is not to be arrested1 so we feel an inclination to follow the progress of the colour1 not1 however1 as in the case of the red-yellow1 to see it still increase in the active sense1 but to find a point to rest in4 #ghi4 ,in a very attenuated state1 this colour is known to us under the name of lilac2 but even in this degree it has a something lively without gladness4 #gij4 ,this unquiet feeling increases as the hue progresses1 and it may be safely assumed1 that a carpet of a perfectly pure deep blue-red would be intolerable4 ,on this account1 when it is used for dress1 ribbons1 or other ornaments1 it is employed in a very attenuated and light state1 and thus displays its character as above defined1 in a peculiarly attractive manner4 #gia4 ,as the higher dignitaries of the church have appropriated this unquiet colour to themselves1 we may venture to say that it unceasingly aspires to the cardinal's red through the restless degrees of a still impatient progression4 ,,red4 #gib4 ,we are here to forget everything that borders on yellow or blue4 ,we are to imagine an absolutely pure red1 like fine carmine suffered to dry on white porcelain4 ,we have called this colour purpur by way of distinction1 although we are quite aware that the purple of the ancients inclined more to blue4 #gic4 ,whoever is acquainted with the prismatic origin of red1 will not think it paradoxical if we assert that this colour partly actu1 partly potenti1 includes all the other colours4 #gid4 ,we have remarked a constant progress or augmentation in yellow and blue1 and seen what impressions were produced by the various states2 hence it may naturally be inferred that now1 in the junction of the deepened extremes1 a feeling of satisfaction must succeed2 and thus1 in physical phenomena1 this highest of all appearances of colour arises from the junction of two contrasted extremes which have gradually prepared themselves for a union4 #gie4 ,as a pigment1 on the other hand1 it presents itself to us already formed1 and is most perfect as a hue in cochineal2 a substance which1 however1 by chemical action may be made to tend to the plus or the minus side1 and may be considered to have attained the central point in the best carmine4 #gif4 ,the effect of this colour is as peculiar as its nature4 ,it conveys an impression of gravity and dignity1 and at the same time of grace and attractiveness4 ,the first in its dark deep state1 the latter in its light attenuated tint2 and thus the dignity of age and the amiableness of youth may adorn itself with degrees of the same hue4 #gig4 ,history relates many instances of the jealousy of sovereigns with regard to the quality of red4 ,surrounding accompaniments of this colour have always a grave and magnificent effect4 #gih4 ,the red glass exhibits a bright landscape in so dreadful a hue as to inspire sentiments of awe4 #gii4 ,kermes and cochineal1 the two materials chiefly employed in dyeing to produce this colour1 incline more or less to the plus or minus state1 and may be made to pass and repass the culminating point by the action of acids and alkalis3 it is to be observed that the ,french arrest their operations on the active side1 as is proved by the ,french scarlet1 which inclines to yellow4 ,the ,italians1 on the other hand1 remain on the passive side1 for their scarlet has a tinge of blue4 #hjj4 ,by means of a similar alkaline treatment1 the so-called crimson is produced2 a colour which the ,french must be particularly prejudiced against1 since they employ the expressions--,sot en cramoisi1 mchant en cramoisi1 to mark the extreme of the silly and the reprehensible4 ,,green4 #hja4 ,if yellow and blue1 which we consider as the most fundamental and simple colours1 are united as they first appear1 in the first state of their action1 the colour which we call green is the result4 #hjb4 ,the eye experiences a distinctly grateful impression from this colour4 ,if the two elementary colours are mixed in perfect equality so that neither predominates1 the eye and the mind repose on the result of this junction as upon a simple colour4 ,the beholder has neither the wish nor the power to imagine a state beyond it4 ,hence for rooms to live in constantly1 the green colour is most generally selected4 ,,completeness ,,and ,,harmony4 #hjc4 ,we have hitherto assumed1 for the sake of clearer explanation1 that the eye can be compelled to assimilate or identify itself with a single colour2 but this can only be possible for an instant4 #hjd4 ,for when we find ourselves surrounded by a given colour which excites its corresponding sensation on the eye1 and compels us by its presence to remain in a state identical with it1 this state is soon found to be forced1 and the organ unwillingly remains in it4 #hje4 ,when the eye sees a colour it is immediately excited1 and it is its nature1 spontaneously and of necessity1 at once to produce another1 which with the original colour comprehends the whole chromatic scale4 ,a single colour excites1 by a specific sensation1 the tendency to universality4 #hjf4 ,to experience this completeness1 to satisfy itself1 the eye seeks for a colourless space next every hue in order to produce the complemental hue upon it4 #hjg4 ,in this resides the fundamental law of all harmony of colours1 of which every one may convince himself by making himself accurately acquainted with the experiments which we have described in the chapter on the physiological colours4 #hjh4 ,if1 again1 the entire scale is presented to the eye externally1 the impression is gladdening1 since the result of its own operation is presented to it in reality4 ,we turn our attention therefore1 in the first place1 to this harmonious juxtaposition4 #hji4 ,as a very simple means of comprehending the principle of this1 the reader has only to imagine a moveable diametrical index in the colorific circle4#a ,the index1 as it revolves round the whole circle1 indicates at its two extremes the complemental colours1 which1 after all1 may be reduced to three contrasts4 #haj4 ,yellow demands ,red-blue1 ,blue demands ,red-yellow1 ,red demands ,green1 and contrariwise4 #haa4 ,in proportion as one end of the supposed index deviates from the central intensity of the colours1 arranged as they are in the natural order1 so the opposite end changes its place in the contrasted gradation1 and by such a simple contrivance the complemental colours may be indicated at any given point4 ,a chromatic circle might be made for this purpose1 not confined1 like our own1 to the leading colours1 but exhibiting them with their transitions in an unbroken series4 ,this would not be without its use1 for we are here considering a very important point which deserves all our attention4#b #hab4 ,we before stated that the eye could be in some degree pathologically affected by being long confined to a single colour2 that1 again1 definite moral impressions were thus produced1 at one time lively and aspiring1 at another susceptible and anxious--now exalted to grand associations1 now reduced to ordinary ones4 ,we now observe that the demand for completeness1 which is inherent in the organ1 frees us from this restraint2 the eye relieves itself by producing the opposite of the single colour forced upon it1 and thus attains the entire impression which is so satisfactory to it4 #hac4 ,simple1 therefore1 as these strictly harmonious contrasts are1 as presented to us in the narrow circle1 the hint is important1 that nature tends to emancipate the sense from confined impressions by suggesting and producing the whole1 and that in this instance we have a natural phenomenon immediately applicable to sthetic purposes4 #had4 ,while1 therefore1 we may assert that the chromatic scale1 as given by us1 produces an agreeable impression by its ingredient hues1 we may here remark that those have been mistaken who have hitherto adduced the rainbow as an example of the entire scale2 for the chief colour1 pure red1 is deficient in it1 and cannot be produced1 since in this phenomenon1 as well as in the ordinary prismatic series1 the yellow-red and blue-red cannot attain to a union4 #hae4 ,nature perhaps exhibits no general phenomenon where the scale is in complete combination4 ,by artificial experiments such an appearance may be produced in its perfect splendour4 ,the mode1 however1 in which the entire series is connected in a circle1 is rendered most intelligible by tints on paper1 till after much experience and practice1 aided by due susceptibility of the organ1 we become penetrated with the idea of this harmony1 and feel it present in our minds4 #haf4 ,besides these pure1 harmonious1 self-developed combinations1 which always carry the conditions of completeness with them1 there are others which may be arbitrarily produced1 and which may be most easily described by observing that they are to be found in the colorific circle1 not by diameters1 but by chords1 in such a manner that an intermediate colour is passed over4 #hag4 ,we call these combinations characteristic because they have all a certain significancy and tend to excite a definite impression2 an impression1 however1 which does not altogether satisfy1 inasmuch as every characteristic quality of necessity presents itself only as a part of a whole1 with which it has a relation1 but into which it cannot be resolved4 #hah4 ,as we are acquainted with the impressions produced by the colours singly as well as in their harmonious relations1 we may at once conclude that the character of the arbitrary combinations will be very different from each other as regards their significancy4 ,we proceed to review them separately4 ,,yellow ,,and ,,blue4 #hai4 ,this is the simplest of such combinations4 ,it may be said that it contains too little1 for since every trace of red is wanting in it1 it is defective as compared with the whole scale4 ,in this view it may be called poor1 and as the two contrasting elements are in their lowest state1 may be said to be ordinary2 yet it is recommended by its proximity to green--in short1 by containing the ingredients of an ultimate state4 ,,yellow ,,and ,,red4 #hbj4 ,this is a somewhat preponderating combination1 but it has a serene and magnificent effect4 ,the two extremes of the active side are seen together without conveying any idea of progression from one to the other4 ,as the result of their combination in pigments is yellow-red1 so they in some degree represent this colour4 ,,blue ,,and ,,red4 #hba4 ,the two ends of the passive side1 with the excess of the upper end of the active side4 ,the effect of this juxtaposition approaches that of the blue-red produced by their union4 ,,yellow-,,red ,,and ,,blue-,,red4 #hbb4 ,these1 when placed together1 as the deepened extremes of both sides1 have something exciting1 elevated3 they give us a presentiment of red1 which in physical experiments is produced by their union4 #hbc4 ,these four combinations have also the common quality of producing the intermediate colour of our colorific circle by their union1 a union which actually takes place if they are opposed to each other in small quantities and seen from a distance4 ,a surface covered with narrow blue and yellow stripes appears green at a certain distance4 #hbd4 ,if1 again1 the eye sees blue and yellow next each other1 it finds itself in a peculiar disposition to produce green without accomplishing it1 while it neither experiences a satisfactory sensation in contemplating the detached colours1 nor an impression of completeness in the two4 #hbe4 ,thus it will be seen that it was not without reason we called these combinations characteristic2 the more so1 since the character of each combination must have a relation to that of the single colours of which it consists4 ,,combinations ,,non-,,characteristic4 #hbf4 ,we now turn our attention to the last kind of combinations4 ,these are easily found in the circle2 they are indicated by shorter chords1 for in this case we do not pass over an entire intermediate colour1 but only the transition from one to the other4 #hbg4 ,these combinations may justly be called non-characteristic1 inasmuch as the colours are too nearly alike for their impression to be significant4 ,yet most of these recommend themselves to a certain degree1 since they indicate a progressive state1 though its relations can hardly be appreciable4 #hbh4 ,thus yellow and yellow-red1 yellow-red and red1 blue and blue-red1 blue-red and red1 represent the nearest degrees of augmentation and culmination1 and in certain relations as to quantity may produce no unpleasant effect4 #hbi4 ,the juxtaposition of yellow and green has always something ordinary1 but in a cheerful sense2 blue and green1 on the other hand1 is ordinary in a repulsive sense4 ,our good forefathers called these last fool's colours4 ,,relation ,,of ,,the ,,combinations ,,to ,,light ,,and ,,dark4 #hcj4 ,these combinations may be very much varied by making both colours light or both dark1 or one light and the other dark2 in which modifications1 however1 all that has been found true in a general sense is applicable to each particular case4 ,with regard to the infinite variety thus produced1 we merely observe3 #hca4 ,the colours of the active side placed next to black gain in energy1 those of the passive side lose4 ,the active conjoined with white and brightness lose in strength1 the passive gain in cheerfulness4 ,red and green with black appear dark and grave2 with white they appear gay4 #hcb4 ,to this we may add that all colours may be more or less broken or neutralised1 may to a certain degree be rendered nameless1 and thus combined partly together and partly with pure colours2 but although the relations may thus be varied to infinity1 still all that is applicable with regard to the pure colours will be applicable in these cases4 ,,considerations ,,derived ,,from ,,the ,,evidence ,,of ,,experience ,,and ,,history4 #hcc4 ,the principles of the harmony of colours having been thus far defined1 it may not be irrelevant to review what has been adduced in connexion with experience and historical examples4 #hcd4 ,the principles in question have been derived from the constitution of our nature and the constant relations which are found to obtain in chromatic phenomena4 ,in experience we find much that is in conformity with these principles1 and much that is opposed to them4 #hce4 ,men in a state of nature1 uncivilised nations1 children1 have a great fondness for colours in their utmost brightness1 and especially for yellow-red3 they are also pleased with the motley4 ,by this expression we understand the juxtaposition of vivid colours without an harmonious balance2 but if this balance is observed1 through instinct or accident1 an agreeable effect may be produced4 ,i remember a ,hessian officer1 returned from ,america1 who had painted his face with the positive colours1 in the manner of the ,indians2 a kind of completeness or due balance was thus produced1 the effect of which was not disagreeable4 #hcf4 ,the inhabitants of the south of ,europe make use of very brilliant colours for their dresses4 ,the circumstance of their procuring silk stuffs at a cheap rate is favourable to this propensity4 ,the women1 especially1 with their bright-coloured bodices and ribbons1 are always in harmony with the scenery1 since they cannot possibly surpass the splendour of the sky and landscape4 #hcg4 ,the history of dyeing teaches us that certain technical conveniences and advantages have had great influence on the costume of nations4 ,we find that the ,germans wear blue very generally because it is a permanent colour in cloth2 so in many districts all the country people wear green twill1 because that material takes a green dye well4 ,if a traveller were to pay attention to these circumstances1 he might collect some amusing and curious facts4 #hch4 ,colours1 as connected with particular frames of mind1 are again a consequence of peculiar character and circumstances4 ,lively nations1 the ,french for instance1 love intense colours1 especially on the active side2 sedate nations1 like the ,english and ,germans1 wear straw-coloured or leather-coloured yellow accompanied with dark blue4 ,nations aiming at dignity of appearance1 the ,spaniards and ,italians for instance1 suffer the red colour of their mantles to incline to the passive side4 #hci4 ,in dress we associate the character of the colour with the character of the person4 ,we may thus observe the relation of colours singly1 and in combination1 to the colour of the complexion1 age1 and station4 #hdj4 ,the female sex in youth is attached to rose-colour and sea-green1 in age to violet and dark-green4 ,the fair-haired prefer violet1 as opposed to light yellow1 the brunettes1 blue1 as opposed to yellow-red1 and all on good grounds4 ,the ,roman emperors were extremely jealous with regard to their purple4 ,the robe of the ,chinese ,emperor is orange embroidered with red2 his attendants and the ministers of religion wear citron-yellow4 #hda4 ,people of refinement have a disinclination to colours4 ,this may be owing partly to weakness of sight1 partly to the uncertainty of taste1 which readily takes refuge in absolute negation4 ,women now appear almost universally in white and men in black4 #hdb4 ,an observation1 very generally applicable1 may not be out of place here1 namely1 that man1 desirous as he is of being distinguished1 is quite as willing to be lost among his fellows4 #hdc4 ,black was intended to remind the ,venetian noblemen of republican equality4 #hdd4 ,to what degree the cloudy sky of northern climates may have gradually banished colour may also admit of explanation4 #hde4 ,the scale of positive colours is obviously soon exhausted2 on the other hand1 the neutral1 subdued1 so-called fashionable colours present infinitely varying degrees and shades1 most of which are not unpleasing4 #hdf4 ,it is also to be remarked that ladies1 in wearing positive colours1 are in danger of making a complexion which may not be very bright still less so1 and thus to preserve a due balance with such brilliant accompaniments1 they are induced to heighten their complexions artificially4 #hdg4 ,an amusing inquiry might be made which would lead to a critique of uniforms1 liveries1 cockades1 and other distinctions1 according to the principles above hinted at4 ,it might be observed1 generally1 that such dresses and insignia should not be composed of harmonious colours4 ,uniforms should be characteristic and dignified2 liveries might be ordinary and striking to the eye4 ,examples both good and bad would not be wanting1 since the scale of colours usually employed for such purposes is limited1 and its varieties have been often enough tried4#c ,,sthetic ,,influence4 #hdh4 ,from the moral associations connected with the appearance of colours1 single or combined1 their sthetic influence may now be deduced for the artist4 ,we shall touch the most essential points to be attended to after first considering the general condition of pictorial representation1 light and shade1 with which the appearance of colour is immediately connected4 ,,chiaro-,,scuro4 #hdi4 ,we apply the term chiaro-scuro 7,helldunkel7 to the appearance of material objects when the mere effect produced on them by light and shade is considered4--,note ,d ,d4 #hej4 ,in a narrower sense a mass of shadow lighted by reflexes is often thus designated2 but we here use the expression in its first and more general sense4 #hea4 ,the separation of light and dark from all appearance of colour is possible and necessary4 ,the artist will solve the mystery of imitation sooner by first considering light and dark independently of colour1 and making himself acquainted with it in its whole extent4 #heb4 ,chiaro-scuro exhibits the substance as substance1 inasmuch as light and shade inform us as to degrees of density4 #hec4 ,we have here to consider the highest light1 the middle tint1 and the shadow1 and in the last the shadow of the object itself1 the shadow it casts on other objects1 and the illumined shadow or reflexion4 #hed4 ,the globe is well adapted for the general exemplification of the nature of chiaro-scuro1 but it is not altogether sufficient4 ,the softened unity of such complete rotundity tends to the vapoury1 and in order to serve as a principle for effects of art1 it should be composed of plane surfaces1 so as to define the gradations more4 #hee4 ,the ,italians call this manner il piazzoso2 in ,german it might be called das ,flchenhafte4#d ,if1 therefore1 the sphere is a perfect example of natural chiaro-scuro1 a polygon would exhibit the artist-like treatment in which all kinds of lights1 half-lights1 shadows1 and reflexions1 would be appreciable4--,note ,e ,e4 #hef4 ,the bunch of grapes is recognised as a good example of a picturesque completeness in chiaro-scuro1 the more so as it is fitted1 from its form1 to represent a principal group2 but it is only available for the master who can see in it what he has the power of producing4 #heg4 ,in order to make the first idea intelligible to the beginner1 7for it is difficult to consider it abstractedly even in a polygon17 we may take a cube1 the three sides of which that are seen represent the light1 the middle tint1 and the shadow in distinct order4 #heh4 ,to proceed again to the chiaro-scuro of a more complicated figure1 we might select the example of an open book1 which presents a greater diversity4 #hei4 ,we find the antique statues of the best time treated very much with reference to these effects4 ,the parts intended to receive the light are wrought with simplicity1 the portion originally in shade is1 on the other hand1 in more distinct surfaces to make them susceptible of a variety of reflexions2 here the example of the polygon will be remembered4--,note ,f ,f4 #hfj4 ,the pictures of ,herculaneum and the ,aldobrandini marriage are examples of antique painting in the same style4 #hfa4 ,modern examples may be found in single figures by ,raphael1 in entire works by ,correggio1 and also by the ,flemish masters1 especially ,rubens4 ,,tendency ,,to ,,colour4 #hfb4 ,a picture in black and white seldom makes its appearance2 some works of ,polidoro are examples of this kind of art4 ,such works1 inasmuch as they can attain form and keeping1 are estimable1 but they have little attraction for the eye1 since their very existence supposes a violent abstraction4 #hfc4 ,if the artist abandons himself to his feeling1 colour presently announces itself4 ,black no sooner inclines to blue than the eye demands yellow1 which the artist instinctively modifies1 and introduces partly pure in the light1 partly reddened and subdued as brown1 in the reflexes1 thus enlivening the whole4--,note ,g ,g4 #hfd4 ,all kinds of camayeu1 or colour on similar colour1 end in the introduction either of a complemental contrast1 or some variety of hue4 ,thus1 ,polidoro in his black and white frescoes sometimes introduced a yellow vase1 or something of the kind4 #hfe4 ,in general it may be observed that men have at all times instinctively striven after colour in the practice of the art4 ,we need only observe daily1 how soon amateurs proceed from colourless to coloured materials4 ,paolo ,uccello painted coloured landscapes to colourless figures4--,note ,h ,h4 #hff4 ,even the sculpture of the ancients could not be exempt from the influence of this propensity4 ,the ,egyptians painted their bas-reliefs2 statues had eyes of coloured stones4 ,porphyry draperies were added to marble heads and extremities1 and variegated stalactites were used for the pedestals of busts4 ,the ,jesuits did not fail to compose the statue of their ,s4 ,luigi1 in ,rome1 in this manner1 and the most modern sculpture distinguishes the flesh from the drapery by staining the latter4 ,,keeping4 #hfg4 ,if linear perspective displays the gradation of objects in their apparent size as affected by distance1 arial perspective shows us their gradation in greater or less distinctness1 as affected by the same cause4 #hfh4 ,although from the nature of the organ of sight1 we cannot see distant objects so distinctly as nearer ones1 yet arial perspective is grounded strictly on the important fact that all mediums called transparent are in some degree dim4 #hfi4 ,the atmosphere is thus always1 more or less1 semi-transparent4 ,this quality is remarkable in southern climates1 even when the barometer is high1 the weather dry1 and the sky cloudless1 for a very pronounced gradation is observable between objects but little removed from each other4 #hgj4 ,the appearance on a large scale is known to every one2 the painter1 however1 sees or believes he sees1 the gradation in the slightest varieties of distance4 ,he exemplifies it practically by making a distinction1 for instance1 in the features of a face according to their relative position as regards the plane of the picture4 ,the direction of the light is attended to in like manner4 ,this is considered to produce a gradation from side to side1 while keeping has reference to depth1 to the comparative distinctness of near and distant things4 #hga4 ,in proceeding to consider this subject1 we assume that the painter is generally acquainted with our sketch of the theory of colours1 and that he has made himself well acquainted with certain chapters and rubrics which especially concern him4 ,he will thus be enabled to make use of theory as well as practice in recognising the principles of effect in nature1 and in employing the means of art4 ,,colour ,,in ,,general ,,nature4 #hgb4 ,the first indication of colour announces itself in nature together with the gradations of arial perspective2 for arial perspective is intimately connected with the doctrine of semi-transparent mediums4 ,we see the sky1 distant objects and even comparatively near shadows1 blue4 ,at the same moment1 the illuminating and illuminated objects appear yellow1 gradually deepening to red4 ,in many cases the physiological suggestion of contrasts comes into the account1 and an entirely colourless landscape1 by means of these assisting and counteracting tendencies1 appears to our eyes completely coloured4 #hgc4 ,local colours are composed of the general elementary colours2 but these are determined or specified according to the properties of substances and surfaces on which they appear3 this specification is infinite4 #hgd4 ,thus1 there is at once a great difference between silk and wool similarly dyed4 ,every kind of preparation and texture produces corresponding modifications4 ,roughness1 smoothness1 polish1 all are to be considered4 #hge4 ,it is therefore one of the pernicious prejudices of art that the skilful painter must never attend to the material of draperies1 but always represent1 as it were1 only abstract folds4 ,is not all characteristic variety thus done away with1 and is the portrait of ,leo ,x4 less excellent because velvet1 satin1 and moreen1 are imitated in their relative effect8 #hgf4 ,in the productions of nature1 colours appear more or less modified1 specified1 even individualised3 this may be readily observed in minerals and plants1 in the feathers of birds and the skins of beasts4 #hgg4 ,the chief art of the painter is always to imitate the actual appearance of the definite hue1 doing away with the recollection of the elementary ingredients of colour4 ,this difficulty is in no instance greater than in the imitation of the surface of the human figure4 #hgh4 ,the colour of flesh1 as a whole1 belongs to the active side1 yet the bluish of the passive side mingles with it4 ,the colour is altogether removed from the elementary state and neutralised by organisation4 #hgi4 ,to bring the colouring of general nature into harmony with the colouring of a given object1 will perhaps be more attainable for the judicious artist after the consideration of what has been pointed out in the foregoing theory4 ,for the most fancifully beautiful and varied appearances may still be made true to the principles of nature4 ,,characteristic ,,colouring4 #hhj4 ,the combination of coloured objects1 as well as the colour of their ground1 should depend on considerations which the artist pre-establishes for himself4 ,here a reference to the effect of colours singly or combined1 on the feelings1 is especially necessary4 ,on this account the painter should possess himself with the idea of the general dualism1 as well as of particular contrasts1 not forgetting what has been adverted to with regard to the qualities of colours4 #hha4 ,the characteristic in colour may be comprehended under three leading rubrics1 which we here define as the powerful1 the soft1 and the splendid4 #hhb4 ,the first is produced by the preponderance of the active side1 the second by that of the passive side1 and the third by completeness1 by the exhibition of the whole chromatic scale in due balance4 #hhc4 ,the powerful impression is attained by yellow1 yellow-red1 and red1 which last colour is to be arrested on the plus side4 ,but little violet and blue1 still less green1 are admissible4 ,the soft effect is produced by blue1 violet1 and red1 which in this case is arrested on the minus side2 a moderate addition of yellow and yellow-red1 but much green may be admitted4 #hhd4 ,if it is proposed to produce both these effects in their full significancy1 the complemental colours may be excluded to a minimum1 and only so much of them may be suffered to appear as is indispensable to convey an impression of completeness4 ,,harmonious ,,colouring4 #hhe4 ,although the two characteristic divisions as above defined may in some sense be also called harmonious1 the harmonious effect1 properly so called1 only takes place when all the colours are exhibited together in due balance4 #hhf4 ,in this way the splendid as well as the agreeable may be produced2 both of these1 however1 have of necessity a certain generalised effect1 and in this sense may be considered the reverse of the characteristic4 #hhg4 ,this is the reason why the colouring of most modern painters is without character1 for1 while they follow their general instinctive feeling only1 the last result of such a tendency must be mere completeness2 this1 they more or less attain1 but thus at the same time neglect the characteristic impression which the subject might demand4 #hhh4 ,but if the principles before alluded to are kept in view1 it must be apparent that a distinct style of colour may be adopted on safe grounds for every subject4 ,the application requires1 it is true1 infinite modifications1 which can only succeed in the hands of genius4 ,,genuine ,,tone4 #hhi4 ,if the word tone1 or rather tune1 is to be still borrowed in future from music1 and applied to colouring1 it might be used in a better sense than heretofore4 #hij4 ,for it would not be unreasonable to compare a painting of powerful effect1 with a piece of music in a sharp key2 a painting of soft effect with a piece of music in a flat key1 while other equivalents might be found for the modifications of these two leading modes4 ,,false ,,tone4 #hia4 ,the word tone has been hitherto understood to mean a veil of a particular colour spread over the whole picture2 it was generally yellow1 for the painter instinctively pushed the effect towards the powerful side4 #hib4 ,if we look at a picture through a yellow glass it will appear in this tone4 ,it is worth while to make this experiment again and again1 in order to observe what takes place in such an operation4 ,it is a sort of artificial light1 deepening1 and at the same time darkening the plus side1 and neutralising the minus side4 #hic4 ,this spurious tone is produced instinctively through uncertainty as to the means of attaining a genuine effect2 so that instead of completeness1 monotony is the result4 ,,weak ,,colouring4 #hid4 ,it is owing to the same uncertainty that the colours are sometimes so much broken as to have the effect of a grey camayeu1 the handling being at the same time as delicate as possible4 #hie4 ,the harmonious contrasts are often found to be very happily felt in such pictures1 but without spirit1 owing to a dread of the motley4 ,,the ,,motley4 #hif4 ,a picture may easily become party-coloured or motley1 when the colours are placed next each other in their full force1 as it were only mechanically and according to uncertain impressions4 #hig4 ,if1 on the other hand1 weak colours are combined1 even although they may be dissonant1 the effect1 as a matter of course1 is not striking4 ,the uncertainty of the artist is communicated to the spectator1 who1 on his side1 can neither praise nor censure4 #hih4 ,it is also important to observe that the colours may be disposed rightly in themselves1 but that a work may still appear motley1 if they are falsely arranged in relation to light and shade4 #hii4 ,this may the more easily occur as light and shade are already defined in the drawing1 and are1 as it were1 comprehended in it1 while the colour still remains open to selection4 ,,dread ,,of ,,theory4 #ijj4 ,a dread of1 nay1 a decided aversion for all theoretical views respecting colour and everything belonging to it1 has been hitherto found to exist among painters2 a prejudice for which1 after all1 they were not to be blamed2 for what has been hitherto called theory was groundless1 vacillating1 and akin to empiricism4 ,we hope that our labours may tend to diminish this prejudice1 and stimulate the artist practically to prove and embody the principles that have been explained4 ,,ultimate ,,aim4 #ija4 ,but without a comprehensive view of the whole of our theory1 the ultimate object will not be attained4 ,let the artist penetrate himself with all that we have stated4 ,it is only by means of harmonious relations in light and shade1 in keeping1 in true and characteristic colouring1 that a picture can be considered complete1 in the sense we have now learnt to attach to the term4 ,,grounds4 #ijb4 ,it was the practice of the earlier artists to paint on light grounds4 ,this ground consisted of gypsum1 and was thickly spread on linen or panel1 and then levigated4 ,after the outline was drawn1 the subject was washed in with a blackish or brownish colour4 ,pictures prepared in this manner for colouring are still in existence1 by ,leonardo da ,vinci1 and ,fra ,bartolomeo2 there are also several by ,guido4--,note ,i ,i4 #ijc4 ,when the artist proceeded to colour1 and had to represent white draperies1 he sometimes suffered the ground to remain untouched4 ,titian did this latterly when he had attained the greatest certainty in practice1 and could accomplish much with little labour4 ,the whitish ground was left as a middle tint1 the shadows painted in1 and the high lights touched on4--,note ,k ,k4 #ijd4 ,in the process of colouring1 the preparation merely washed as it were underneath1 was always effective4 ,a drapery1 for example1 was painted with a transparent colour1 the white ground shone through it and gave the colour life1 so the parts previously prepared for shadows exhibited the colour subdued1 without being mixed or sullied4 #ije4 ,this method had many advantages2 for the painter had a light ground for the light portions of his work and a dark ground for the shadowed portions4 ,the whole picture was prepared2 the artist could work with thin colours in the shadows1 and had always an internal light to give value to his tints4 ,in our own time painting in water colours depends on the same principles4 #ijf4 ,indeed a light ground is now generally employed in oil-painting1 because middle tints are thus found to be more transparent1 and are in some degree enlivened by a bright ground2 the shadows1 again1 do not so easily become black4 #ijg4 ,it was the practice for a time to paint on dark grounds4 ,tintoret probably introduced them4 ,titian's best pictures are not painted on a dark ground4 #ijh4 ,the ground in question was red-brown1 and when the subject was drawn upon it1 the strongest shadows were laid in2 the colours of the lights impasted very thickly in the bright parts1 and scumbled towards the shadows1 so that the dark ground appeared through the thin colour as a middle tint4 ,effect was attained in finishing by frequently going over the bright parts and touching on the high lights4 #iji4 ,if this method especially recommended itself in practice on account of the rapidity it allowed of1 yet it had pernicious consequences4 ,the strong ground increased and became darker1 and the light colours losing their brightness by degrees1 gave the shadowed portions more and more preponderance4 ,the middle tints became darker and darker1 and the shadows at last quite obscure4 ,the strongly impasted lights alone remained bright1 and we now see only light spots on the painting4 ,the pictures of the ,bolognese school1 and of ,caravaggio1 afford sufficient examples of these results4 #iaj4 ,we may here in conclusion observe1 that glazing derives its effect from treating the prepared colour underneath as a light ground4 ,by this operation colours may have the effect of being mixed to the eye1 may be enhanced1 and may acquire what is called tone2 but they thus necessarily become darker4 ,,pigments4 #iaa4 ,we receive these from the hands of the chemist and the investigator of nature4 ,much has been recorded respecting colouring substances1 which is familiar to all by means of the press4 ,but such directions require to be revised from time to time4 ,the master meanwhile communicates his experience in these matters to his scholar1 and artists generally to each other4 #iab4 ,those pigments which according to their nature are the most permanent1 are naturally much sought after1 but the mode of employing them also contributes much to the duration of a picture4 ,the fewest possible colouring materials are to be employed1 and the simplest methods of using them cannot be sufficiently recommended4 #iac4 ,for from the multitude of pigments colouring has suffered much4 ,every pigment has its peculiar nature as regards its effect on the eye2 besides this it has its peculiar quality1 requiring a corresponding technical method in its application4 ,the former circumstance is a reason why harmony is more difficult of attainment with many materials than with few1 the latter1 why chemical action and re-action may take place among the colouring substances4 #iad4 ,we may refer1 besides1 to some false tendencies which the artists suffer themselves to be led away with4 ,painters are always looking for new colouring substances1 and believe when such a substance is discovered that they have made an advance in the art4 ,they have a great curiosity to know the practical methods of the old masters1 and lose much time in the search4 ,towards the end of the last century we were thus long tormented with wax-painting4 ,others turn their attention to the discovery of new methods1 through which nothing new is accomplished2 for1 after all1 it is the feeling of the artist only that informs every kind of technical process4 ,,allegorical1 ,,symbolical1 ,,mystical ,,application ,,of ,,colour4 #iae4 ,it has been circumstantially shown above1 that every colour produces a distinct impression on the mind1 and thus addresses at once the eye and feelings4 ,hence it follows that colour may be employed for certain moral and sthetic ends4 #iaf4 ,such an application1 coinciding entirely with nature1 might be called symbolical1 since the colour would be employed in conformity with its effect1 and would at once express its meaning4 ,if1 for example1 pure red were assumed to designate majesty1 there can be no doubt that this would be admitted to be a just and expressive symbol4 ,all this has been already sufficiently entered into4 #iag4 ,another application is nearly allied to this2 it might be called the allegorical application4 ,in this there is more of accident and caprice1 inasmuch as the meaning of the sign must be first communicated to us before we know what it is to signify2 what idea1 for instance1 is attached to the green colour1 which has been appropriated to hope8 #iah4 ,that1 lastly1 colour may have a mystical allusion1 may be readily surmised1 for since every diagram in which the variety of colours may be represented points to those primordial relations which belong both to nature and the organ of vision1 there can be no doubt that these may be made use of as a language1 in cases where it is proposed to express similar primordial relations which do not present themselves to the senses in so powerful and varied a manner4 ,the mathematician extols the value and applicability of the triangle2 the triangle is revered by the mystic2 much admits of being expressed in it by diagrams1 and1 among other things1 the law of the phenomena of colours2 in this case1 indeed1 we presently arrive at the ancient mysterious hexagon4 #iai4 ,when the distinction of yellow and blue is duly comprehended1 and especially the augmentation into red1 by means of which the opposite qualities tend towards each other and become united in a third2 then1 certainly1 an especially mysterious interpretation will suggest itself1 since a spiritual meaning may be connected with these facts2 and when we find the two separate principles producing green on the one hand and red in their intenser state1 we can hardly refrain from thinking in the first case on the earthly1 in the last on the heavenly1 generation of the ,elohim4--,note ,l ,l4 #ibj4 ,but we shall do better not to expose ourselves1 in conclusion1 to the suspicion of enthusiasm2 since1 if our doctrine of colours finds favour1 applications and allusions1 allegorical1 symbolical1 and mystical1 will not fail to be made1 in conformity with the spirit of the age4 ,,concluding ,,observations4 ,in reviewing this labour1 which has occupied me long1 and which at last ,i give but as a sketch1 ,i am reminded of a wish once expressed by a careful writer1 who observed that he would gladly see his works printed at once as he conceived them1 in order then to go to the task with a fresh eye2 since everything defective presents itself to us more obviously in print than even in the cleanest manuscript4 ,this feeling may be imagined to be stronger in my case1 since ,i had not even an opportunity of going through a fair transcript of my work before its publication1 these pages having been put together at a time when a quiet1 collected state of mind was out of the question4#e ,some of the explanations ,i was desirous of giving are to be found in the introduction1 but in the portion of my work to be devoted to the history of the doctrine of colours1 ,i hope to give a more detailed account of my investigations and the vicissitudes they underwent4 ,one inquiry1 however1 may not be out of place here2 the consideration1 namely1 of the question1 what can a man accomplish who cannot devote his whole life to scientific pursuits8 what can he perform as a temporary guest on an estate not his own1 for the advantage of the proprietor8 ,when we consider art in its higher character1 we might wish that masters only had to do with it1 that scholars should be trained by the severest study1 that amateurs might feel themselves happy in reverentially approaching its precincts4 ,for a work of art should be the effusion of genius1 the artist should evoke its substance and form from his inmost being1 treat his materials with sovereign command1 and make use of external influences only to accomplish his powers4 ,but if the professor in this case has many reasons for respecting the dilettante1 the man of science has every motive to be still more indulgent1 since the amateur here is capable of contributing what may be satisfactory and useful4 ,the sciences depend much more on experiment than art1 and for mere experiment many a votary is qualified4 ,scientific results are arrived at by many means1 and cannot dispense with many hands1 many heads4 ,science may be communicated1 the treasure may be inherited1 and what is acquired by one may be appropriated by many4 ,hence no one perhaps ought to be reluctant to offer his contributions4 ,how much do we not owe to accident1 to mere practice1 to momentary observation4 ,all who are endowed only with habits of attention1 women1 children1 are capable of communicating striking and true remarks4 ,in science it cannot therefore be required1 that he who endeavours to furnish something in its aid should devote his whole life to it1 should survey and investigate it in all its extent2 for this1 in most cases1 would be a severe condition even for the initiated4 ,but if we look through the history of science in general1 especially the history of physics1 we shall find that many important acquisitions have been made by single inquirers1 in single departments1 and very often by unprofessional observers4 ,to whatever direction a man may be determined by inclination or accident1 whatever class of phenomena especially strike him1 excite his interest1 fix his attention1 and occupy him1 the result will still be for the advantage of science3 for every new relation that comes to light1 every new mode of investigation1 even the imperfect attempt1 even error itself is available2 it may stimulate other observers and is never without its use as influencing future inquiry4 ,with this feeling the author himself may look back without regret on his endeavours4 ,from this consideration he can derive some encouragement for the prosecution of the remainder of his task2 and although not satisfied with the result of his efforts1 yet re-assured by the sincerity of his intentions1 he ventures to recommend his past and future labours to the interest of his contemporaries and posterity4 ,multi pertransibunt et augebitur scientia4 #a ,plate #a1 fig4 #c4 #b ,see ,note ,c4 #c ,some early ,italian writers1 ,sicillo1 ,occolti1 ,rinaldi1 and others1 have treated this subject in connexion with the supposed signification of colours4--,t4 #d ,the ,english technical expressions flat and square have an association of mannerism4--,t #e ,towards the close of #ahjf1 when ,weimar was occupied by ,napoleon after the battle of ,jena4--,t4 ,,notes4 ,,note ,a4--,par4 #ah4 ,leonardo da ,vinci observes that a light object relieved on a dark ground appears magnified2 and again1 ,objects seen at a distance appear out of proportion2 this is because the light parts transmit their rays to the eye more powerfully than the dark4 ,a woman's white head-dress once appeared to me much wider than her shoulders1 owing to their being dressed in black4#a ,it is now generally admitted that the excitation produced by light is propagated on the retina a little beyond the outline of the image4 ,professor ,plateau1 of ,ghent1 has devoted a very interesting special memoir to the description and explanation of phenomena of this nature4 ,see his ',mmoire sur l',irradiation1' published in the #aath vol4 of the ,transactions of the ,royal ,academy of ,sciences at ,brussels4#b--,s4 ,f4 ,,note ,b4--,par4 #bc4 ,the duration of ocular spectra produced by strongly exciting the retina1 may be conveniently measured by minutes and seconds2 but to ascertain the duration of more evanescent phenomena1 recourse must be had to other means4 ,the ,chevalier d',arcy 7,mm4 de l',acad4 des ,sc4 #agfe17 endeavoured to ascertain the duration of the impression produced by a glowing coal in the following manner4 ,he attached it to the circumference of a wheel1 the velocity of which was gradually increased until the apparent trace of the object formed a complete circle1 and then measured the duration of a revolution1 which was obviously that of the impression4 ,to ascertain the duration of a revolution it is sufficient merely to know the number of revolutions described in a given time4 ,recently more refined experiments of the same kind have been made by ,professors ,plateau and ,wheatstone4--,s4 ,f4 #a ,trattato della ,pittura1 ,roma1 #ahag1 p4 #adc-bbc4 ,this edition1 published from a ,vatican ,,ms41 contains many observations not included in former editions4 #b ,a few notes 7marked with inverted commas and with the signature ,s4 ,f47 have been kindly furnished by a scientific friend4 ,,note ,c4--,par4 #ej4 ,every treatise on the harmonious combination of colours contains the diagram of the chromatic circle more or less elaborately constructed4 ,these diagrams1 if intended to exhibit the contrasts produced by the action and re-action of the retina1 have one common defect4 ,the opposite colours are made equal in intensity2 whereas the complemental colour pictured on the retina is always less vivid1 and always darker or lighter than the original colour4 ,this variety undoubtedly accords more with harmonious effects in painting4 ,the opposition of two pure hues of equal intensity1 differing only in the abstract quality of colour1 would immediately be pronounced crude and inharmonious4 ,it would not1 however1 be strictly correct to say that such a contrast is too violent2 on the contrary1 it appears the contrast is not carried far enough1 for though differing in colour1 the two hues may be exactly similar in purity and intensity4 ,complete contrast1 on the other hand1 supposes dissimilarity in all respects4 ,in addition to the mere difference of hue1 the eye1 it seems1 requires difference in the lightness or darkness of the hue4 ,the spectrum of a colour relieved as a dark on a light ground1 is a light colour on a dark ground1 and vice vers4 ,thus1 if we look at a bright red wafer on the whitest surface1 the complemental image will be still lighter than the white surface2 if the same wafer is placed on a black surface1 the complemental image will be still darker4 ,the colour of both these spectra may be called greenish1 but it is evident that a colour must be scarcely appreciable as such1 if it is lighter than white and darker than black4 ,it is1 however1 to be remarked1 that the white surface round the light greenish image seems tinged with a reddish hue1 and the black surface round the dark image becomes slightly illuminated with the same colour1 thus in both cases assisting to render the image apparent 7#eh74 ,the difficulty or impossibility of describing degrees of colour in words1 has also had a tendency to mislead1 by conveying the idea of more positive hues than the physiological contrast warrants4 ,thus1 supposing scarlet to be relieved as a dark1 the complemental colour is so light in degree and so faint in colour1 that it should be called a pearly grey2 whereas the theorists1 looking at the quality of colour abstractedly1 would call it a green-blue1 and the diagram would falsely present such a hue equal in intensity to scarlet1 or as nearly equal as possible4 ,even the difference of mass which good taste requires may be suggested by the physiological phenomena1 for unless the complemental image is suffered to fall on a surface precisely as near to the eye as that on which the original colour was displayed1 it appears larger or smaller than the original object 7#bb71 and this in a rapidly increasing proportion4 ,lastly1 the shape itself soon becomes changed 7#bf74 ,that vivid colour demands the comparative absence of colour1 either on a lighter or darker scale1 as its contrast1 may be inferred again from the fact that bright colourless objects produce strongly coloured spectra4 ,in darkness1 the spectrum which is first white1 or nearly white1 is followed by red3 in light1 the spectrum which is first black1 is followed by green 7#ci-dd74 ,all colour1 as the author observes 7#bei71 is to be considered as half-light1 inasmuch as it is in every case lighter than black and darker than white4 ,hence no contrast of colour with colour1 or even of colour with black or white1 can be so great 7as regards lightness or darkness7 as the contrast of black and white1 or light and dark abstractedly4 ,this distinction between the differences of degree and the differences of kind is important1 since a just application of contrast in colour may be counteracted by an undue difference in lightness or darkness4 ,the mere contrast of colour is happily employed in some of ,guido's lighter pictures1 but if intense darks had been opposed to his delicate carnations1 their comparative whiteness would have been unpleasantly apparent4 ,on the other hand1 the flesh-colour in ,giorgione1 ,sebastian del ,piombo 7his best imitator71 and ,titian1 was sometimes so extremely glowing#a that the deepest colours1 and black1 were indispensable accompaniments4 ,the manner of ,titian as distinguished from his imitation of ,giorgione1 is golden rather than fiery1 and his biographers are quite correct in saying that he was fond of opposing red 7lake7 and blue to his flesh#b4 ,the correspondence of these contrasts with the physiological phenomena will be immediately apparent1 while the occasional practice of ,rubens in opposing bright red to a still cooler flesh-colour1 will be seen to be equally consistent4 ,the effect of white drapery 7the comparative absence of colour7 in enhancing the glow of ,titian's flesh-colour1 has been frequently pointed out3#c the shadows of white thus opposed to flesh1 often present1 again1 the physiological contrast1 however delicately1 according to the hue of the carnation4 ,the lights1 on the other hand1 are not1 and probably never were1 quite white1 but from the first1 partook of the quality of depth1 a quality assumed by the colourists to pervade every part of a picture more or less4#d ,it was before observed that the description of colours in words may often convey ideas of too positive a nature1 and it may be remarked generally that the colours employed by the great masters are1 in their ultimate effect1 more or less subdued or broken4 ,the physiological contrasts are1 however1 still applicable in the most comparatively neutral scale4 ,again1 the works of the colourists show that these oppositions are not confined to large masses 7except perhaps in works to be seen only at a great distance72 on the contrary1 they are more or less apparent in every part1 and when at last the direct and intentional operations of the artist may have been insufficient to produce them in their minuter degrees1 the accidental results of glazing and other methods may be said to extend the contrasts to infinity4 ,in such productions1 where every smallest portion is an epitome of the whole1 the eye still appreciates the fascinating effect of contrast1 and the work is pronounced to be true and complete1 in the best sense of the words4 ,the ,venetian method of scumbling and glazing exhibits these minuter contrasts within each other1 and is thus generally considered more refined than the system of breaking the colours1 since it ensures a fuller gradation of hues1 and produces another class of contrasts1 those1 namely1 which result from degrees of transparence and opacity4 ,in some of the ,flemish and ,dutch masters1 and sometimes in ,reynolds1 the two methods are combined in great perfection4 ,the chromatic diagram does not appear to be older than the last century4 ,it is one of those happy adaptations of exacter principles to the objects of taste which might have been expected from ,leonardo da ,vinci4 ,that its true principle was duly felt is abundantly evident from the works of the colourists1 as well as from the general observations of early writers4#e ,the more practical directions occasionally to be met with in the treatises of ,leon ,battista ,alberti1 ,leonardo da ,vinci and others1 are conformable to the same system4 ,some ,italian works1 not written by painters1 which pretend to describe this harmony1 are1 however1 very imperfect4#f ,a passage in ,lodovico ,dolce's ,dialogue on ,colours is perhaps the only one worth quoting4 ,he1 says that writer1 who wishes to combine colours that are agreeable to the eye1 will put grey next dusky orange2 yellow-green next rose-colour2 blue next orange2 dark purple1 black1 next dark-green2 white next black1 and white next flesh-colour4#g ,the ,dialogue on ,painting1 by the same author1 has the reputation of containing some of ,titian's precepts3 if the above passage may be traced to the same source1 it must be confessed that it is almost the only one of the kind in the treatise from which it is taken4 #a ,ardito veramente alquanto1 sanguigno1 e quasi fiammeggiante4--,zanetti della ,pittura ,veneziana1 ,ven4 #agga1 p4 #ij4 ,warm as the flesh colour of the colourists is1 it still never approaches a positive hue1 if we except some examples in frescoes and other works intended to be seen at a great distance4 ,zanetti1 speaking of a fresco by ,giorgione1 now almost obliterated1 compares the colour to un vivo raggio di cocente sole4---,varie ,pitture a fresco dei ,principali ,maestri ,veneziani4 ,ven4 #agfj4 #b ,ridolfi4 #c ,zanetti1 ,i4 ii4 #d ,two great authorities1 divided by more than three centuries1 ,leon ,battista ,alberti and ,reynolds1 have recommended this subdued treatment of white4 ,it is to be remembered1 says the first1 that no surface should be made so white that it cannot be made more so4 ,in white dresses again1 it is necessary to stop far short of the last degree of whiteness4--,della ,pittura1 ,i4 ii41 compare with ,reynolds1 vol4 i4 dis4 #h4 #e ,vasari observes1 ,l'unione nella pittura una discordanza dicolori diversi accordati insime4--,vol4 i4 c4 #ah4 ,this observation is repeated by various writers on art in nearly the same words1 and at last appears in ,sandrart3 ,concordia1 potissimum pictur decus1 in discordi consistit1 et quasi litigio colorum4--,p4 i4 c4 #e4 ,the source1 perhaps1 is ,aristotle3 he observes1 ,we are delighted with harmony1 because it is the union of contrary principles having a ratio to each other4--,problem4 #f ,see ,occolti ,trattato de' ,colori4 ,parma1 #aefh4 #g ,volendo l'uomo accoppiare insime colori che all'occhio dilettino--porr insime il berrettino col leonato2 il verde-giallo con l'incarnato e rosso2 il turchino con l'arangi2 il morello col verde oscuro2 il nero col bianco2 il bianco con l'incarnato4--,dialogo di ,m4 ,lodovico ,dolce nel quale si ragiona della qualit1 diversit1 e propriet de' colori4 ,venezia1 #aefe4 ,,note ,d4--,par4 #ff4 ,in some of these cases there can be no doubt that ,goethe attributes the contrast too exclusively to the physiological cause1 without making sufficient allowance for the actual difference in the colour of the lights4 ,the purely physical nature of some coloured shadows was pointed out by ,pohlmann2 and ,dr4 ,eckermann took some pains to convince ,goethe of the necessity of making such a distinction4 ,goethe at first adhered to his extreme view1 but some time afterwards confessed to ,dr4 ,eckermann1 that in the case of the blue shadows of snow 7#gd71 the reflection of the sky was undoubtedly to be taken into the account4 ,both causes may1 however1 operate together1 he observed1 and the contrast which a warm yellow light demands may heighten the effect of the blue4 ,this was all his opponent contended4#a ,with a few such exceptions1 the general theory of ,goethe with regard to coloured shadows is undoubtedly correct2 the experiments with two candles 7#fh71 and with coloured glass and fluids 7#hj71 as well as the observations on the shadows of snow 7#ge71 are conclusive1 for in all these cases only one light is actually changed in colour1 while the other still assumes the complemental hue4 ,coloured shadows1 ,dr4 ,j4 ,mller observes1 are usually ascribed to the physiological influence of contrast2 the complementary colour presented by the shadow being regarded as the effect of internal causes acting on that part of the retina1 and not of the impression of coloured rays from without4 ,this explanation is the one adopted by ,rumford1 ,goethe1 ,grotthuss1 ,brandes1 ,tourtual1 ,pohlmann1 and most authors who have studied the subject4#b ,in the ,historical ,part the author gives an account of a scarce ,french work1 ,observations sur les ,ombres ,colores1 ,paris1 #aghb4 ,the writer#c concludes that the colour of shadows is as much owing to the light that causes them as to that which 7more faintly7 illumines them4 #a ,eckermann's ,gesprche mit ,goethe1 vol4 ii4 p4 #gf and #bhj4 #b ,elements of ,physiology1 by ,j4 ,mller1 ,m4 ,d41 translated from the ,german by ,william ,baly1 ,m4,d4 ,london1 #ahci4 #c ,anonymous1 having only given the initials ,h4 ,f4 ,t4 ,,note ,e4--,par4 #fi4 ,this opinion of the author is frequently repeated 7#bja1 #cab1 #eia71 and as it seems at first sight to be at variance with a received principle of art1 it may be as well at once to examine it4 ,in order to see the general proposition in its true point of view1 it will be necessary to forget the arbitrary distinctions of light and shade1 and to consider all such modifications between highest brightness and absolute darkness only as so many lesser degrees of light4#a ,the author1 indeed1 by the word shadow1 always understands a lesser light4 ,the received notion1 as stated by ,du ,fresnoy1#b is much too positive and unconditional1 and is only true when we understand the displaying light to comprehend certain degrees of half or reflected light1 and the destroying shade to mean the intensest degree of obscurity4 ,there are degrees of brightness which destroy colour as well as degrees of darkness4#c ,in general1 colour resides in a mitigated light1 but a very little observation shows us that different colours require different degrees of light to display them4 ,leonardo da ,vinci frequently inculcates the general principle above alluded to1 but he as frequently qualifies it2 for he not only remarks that the highest light may be comparative privation of colour1 but observes1 with great truth1 that some hues are best displayed in their fully illumined parts1 some in their reflections1 and some in their half-lights2 and again1 that every colour is most beautiful when lit by reflections from its own surface1 or from a hue similar to its own4#d ,the ,venetians went further than ,leonardo in this view and practice2 and he seems to allude to them when he criticises certain painters1 who1 in aiming at clearness and fulness of colour1 neglected what1 in his eyes1 was of superior importance1 namely1 gradation and force of chiaro-scuro4#e ,that increase of colour supposes increase of darkness1 as so often stated by ,goethe1 may be granted without difficulty4 ,to what extent1 on the other hand1 increase of darkness1 or rather diminution of light1 is accompanied by increase of colour1 is a question which has been variously answered by various schools4 ,examples of the total negation of the principle are not wanting1 nor are they confined to the infancy of the art4 ,instances1 again1 of the opposite tendency are frequent in ,venetian and early ,flemish pictures resembling the augmenting richness of gems or of stained glass3#f indeed1 it is not impossible that the increase of colour in shade1 which is so remarkable in the pictures alluded to1 may have been originally suggested by the rich and fascinating effect of stained glass2 and the ,venetians1 in this as in many other respects1 may have improved on a hint borrowed from the early ,german painters1 many of whom painted on glass4#g ,at all events1 the principle of still increasing in colour in certain hues seems to have been adopted in ,flanders and in ,venice at an early period2#h while ,giorgione1 in carrying the style to the most daring extent1 still recommended it by corresponding grandeur of treatment in other respects4 ,the same general tendency1 except that the technical methods are less transparent1 is1 however1 very striking in some of the painters of the school of ,umbria1 the instructors or early companions of ,raphael4#i ,the influence of these examples1 as well as that of ,fra ,bartolommeo1 in ,florence1 is distinctly to be traced in the works of the great artist just named1 but neither is so marked as the effect of his emulation of a ,venetian painter at a later period4 ,the glowing colour1 sometimes bordering on exaggeration1 which ,raphael adopted in ,rome1 is undoubtedly to be attributed to the rivalry of ,sebastian del ,piombo4 ,this painter1 the best of ,giorgione's imitators1 arrived in ,rome1 invited by ,agostini ,chigi1 in #aeaa1 and the most powerful of ,raphael's frescoes1 the ,heliodorus and ,mass of ,bolsena1 as well as some portraits in the same style1 were painted in the two following years4 ,in the hands of some of ,raphael's scholars1 again1 this extreme warmth was occasionally carried to excess1 particularly by ,pierino del ,vaga1 with whom it often degenerated into redness4 ,the representative of the glowing manner in ,florence was ,fra ,bartolommeo1 and1 in the same quality1 considered abstractedly1 some painters of the school of ,ferrara were second to none4 ,in another ,note 7par4 #agg7 some further considerations are offered1 which may partly explain the prevalence of this style in the beginning of the sixteenth century2 here we merely add1 that the conditions under which the appearance itself is most apparent in nature are perhaps more obvious in ,venice than elsewhere4 ,the colour of general nature may be observed in all places with almost equal convenience1 but with regard to an important quality in living nature1 namely1 the colour of flesh1 perhaps there are no circumstances in which its effects at different distances can be so conveniently compared as when the observer and the observed gradually approach and glide past each other on so smooth an element and in so undisturbed a manner as on the canals and in the gondolas of ,venice2#aj the complexions1 from the peculiar mellow carnations of the ,italian women to the sun-burnt features and limbs of the mariners1 presenting at the same time the fullest variety in another sense4 ,at a certain distance--the colour being always assumed to be unimpaired by interposed atmosphere--the reflections appear kindled to intenser warmth2 the fiery glow of ,giorgione is strikingly apparent2 the colour is seen in its largest relation2 the macchia1#aa an expression so emphatically used by ,italian writers1 appears in all its quantity1 and the reflections being the focus of warmth1 the hue seems to deepen in shade4 ,a nearer view gives the detail of cooler tints more perceptibly1#ab and the forms are at the same time more distinct4 ,hence ,lanzi is quite correct when1 in distinguishing the style of ,titian from that of ,giorgione1 he says that ,titian's was at once more defined and less fiery4#ac ,in a still nearer observation the eye detects the minute lights which ,leonardo da ,vinci says are incompatible with effects such as those we have described#ad and which1 accordingly1 we never find in ,giorgione and ,titian4 ,this large impression of colour1 which seems to require the condition of comparative distance for its full effect1 was most fitly employed by the same great artists in works painted in the open air or for large altar-pieces4 ,their celebrated frescoes on the exterior of the ,fondaco de' ,tedeschi at ,venice1 to judge from their faint remains and the descriptions of earlier writers1 were remarkable for extreme warmth in the shadows4 ,the old frescoes in the open air throughout ,friuli have often the same character1 and1 owing to the fulness of effect which this treatment ensures1 are conspicuous at a very great distance4#ae ,in assuming that the ,venetian painters may have acquired a taste for this breadth#af of colour under the circumstances above alluded to1 it is moreover to be remembered that the time for this agreeable study was the evening2 when the sun had already set behind the hills of ,bassano2 when the light was glowing but diffused2 when shadows were soft--conditions all agreeing with the character of their colouring3#ag above all1 when the hour invited the fairer portion of the population to betake themselves in their gondolas to the lagunes4 ,the scene of this promenade was to the north of ,venice1 the quarter in which ,titian at one time lived4 ,a letter exists written by ,francesco ,priscianese1 giving an account of his supping with the great painter in company with ,jacopo ,nardi1 ,pietro ,aretino1 the sculptor ,sansovino1 and others4 ,the writer speaks of the beauty of the garden1 where the table was prepared1 looking over the lagunes towards ,murano1 which part of the sea1 he continues1 as soon as the sun was down1 was covered with a thousand gondolas1 graced with beautiful women1 and enlivened by the harmony of voices and instruments1 which lasted till midnight1 forming a pleasing accompaniment to our cheerful repast4#ah ,to return to ,goethe3 perhaps the foregoing remarks may warrant the conclusion that his idea of colour in shadow is not irreconcileable with the occasional practice of the best painters4 ,the highest examples of the style thus defined are1 or were1 to be found in the works of ,giorgione#ai and ,titian1 and hence the style itself1 though within that circle few dare walk is to be considered the grandest and most perfect4 ,its possible defects or abuse are not to be dissembled3 in addition to the danger of exaggeration#bj it is seldom united with the plenitude of light and shade1 or with roundness2 yet1 where fine examples of both modes of treatment may be compared1 the charm of colour has perhaps the advantage4#ba ,the difficulty of uniting qualities so different in their nature1 is proved by the very rare instances in which it has been accomplished4 ,tintoret in endeavouring to add chiaro-scuro to ,venetian colour1 in almost every instance fell short of the glowing richness of ,titian4#bb ,giacomo ,bassan and his imitators1 even in their dark effects1 still had the principle of the gem in view3 their light1 in certain hues1 is the minimum of colour1 their lower tones are rich1 their darks intense1 and all is sparkling4#bc ,of the great painters who1 beginning1 on the other hand1 with chiaro-scuro1 sought to combine with it the full richness of colour1 ,correggio1 in the opinion of many1 approached perfection nearest2 but we may perhaps conclude with greater justice that the desired excellence was more completely attained by ,rembrandt than by any of the ,italians4 #a ,leonardo da ,vinci observes3 ,l'ombra diminuzione di luce1 tenebre privazione di luce4 ,and again3 ,sempre il minor lume ombra del lume maggiore4--,trattato della ,pittura1 pp4 #bgd-bii4 ,n4 ,b4 ,the same edition before described has been consulted throughout4 #b ,lux varium vivumque dabit1 nullum umbra colorem4 ,de ,arte ,graphic4 ,know first that light displays and shade destroys ,refulgent nature's variegated dies4--,mason's ,translation4 #c ,a ,spanish writer1 ,diego de ,carvalho e ,sampayo1 quoted by ,goethe 7,farbenlehre1 vol4 ii471 has a similar observation4 ,this destroying effect of light is striking in climates where the sun is powerful1 and was not likely to escape the notice of a ,spaniard4 #d ,trattato1 pp4 #ajc1 #aba1 #abc1 #cbd1 c4 #e ,ib4 pp4 #he1 #acd4 #f ,absolute opacity1 to judge from the older specimens of stained glass1 seems to have been considered inadmissible4 ,the window was to admit light1 however modified and varied1 in the form prescribed by the architect1 and that form was to be preserved4 ,this has been unfortunately lost sight of in some modern glass-painting1 which1 by excluding the light in large masses1 and adopting the opacity of pictures 7the reverse of the influence above alluded to71 has interfered with the architectural symmetry in a manner far from desirable4 ,on the other hand1 if we suppose painting at any period to have aimed at the imitation of stained glass1 such an imitation must of necessity have led to extreme force2 for the painter sets out by substituting a mere white ground for the real light of the sky1 and would thus be compelled to subdue every tone accordingly4 ,in such an imitation his colour would soon deepen to its intensest state2 indeed1 considerable portions of the darker hues would be lost in obscurity4 ,the early ,flemish pictures seldom err on the side of a gay superabundance of colour2 on the contrary1 they are generally remarkable for comparatively cool lights1 for extreme depth1 and a certain subdued splendour1 qualities which would necessarily result from the imitation or influence in question4 #g ,see ,langlois1 ,peinture sur ,verre4 ,rouen1 #ahcb2 ,descamps1 ,la ,vie des ,peintres ,flamands2 and ,gessert1 ,geschichte der ,glasmalerei4 ,stutgard1 #ahci4 ,the antiquity of the glass manufactory of ,murano 7,venice7 is also not to be forgotten4 ,vasari objects to the ,venetian glass1 because it was darker in colour than that of ,flanders1 ,france1 and ,england2 but this very quality was more likely to have an advantageous influence on the style of the early oil-painters4 ,the use of stained glass was1 however1 at no period very general in ,italy4 #h ,zanetti1 ,della ,pittura ,veneziana1 marks the progress of the early ,venetian painters by the gradual use of the warm outline4 ,there are some mosaics in ,st4 ,mark's which have the effect of flesh-colour1 but on examination1 the only red colour used is found to be in the outlines and markings4 ,many of the drawings of the old masters1 heightened with red in the shadows1 have the same effect4 ,in these drawings the artists judiciously avoided colouring the lips and cheeks much1 for this would only have betrayed the want of general colour1 as is observable when statues are so treated4 #i ,andrea di ,luigi1 called ,l',ingegno1 and ,niccolo di ,fuligno1 are cited as the most prominent examples4 ,see ,rumohr1 ,italienische ,forschungen4 ,perogino himself occasionally adopted a very glowing colour4 ,the early ,italian schools which adhered most to the ,byzantine types appear to have been also the most remarkable for depth1 or rather darkness1 of colour4 ,this fidelity to customary representation was sometimes1 as in the schools of ,umbria1 and to a certain extent in those of ,siena and ,bologna1 the result of a religious veneration for the ancient examples2 in others1 as in ,venice1 the circumstance of frequent intercourse with the ,levant is also to be taken into the account4 ,the ,greek pictures of the ,madonna1 not to mention other representations1 were extremely dark1 in exaggerated conformity1 it is supposed1 with the tradition respecting her real complexion 7see ,d',agincourt1 vol4 iv4 p4 #a72 a belief which obtained so late as ,lomazzo's time1 for1 speaking of the ,madonna1 he observes1 ,leggesi per che fu alquanto bruna4 ,giotto1 who with the independence of genius betrayed a certain contempt for these traditions1 failed perhaps to unite improvement with novelty when he substituted a pale white flesh-colour for the traditional brown4 ,some specimens of his works1 still existing at ,padua1 present a remarkable contrast in this respect with the earliest productions of the ,venetian and ,paduan artists4 ,his works at ,florence differ as widely from those of the earlier painters of ,tuscany4 ,this peculiarity was inherited by his imitators1 and at one time almost characterised the ,florentine school4 ,leon ,battista ,alberti was not perhaps the first who objected to it 7,vorrei io che dai pittori fosse comperato il color bianco assai pi caro che le presiosissime gemme4--,della ,pittura1 ,i4 ii47 ,the attachment of ,fra ,bartolommeo to the grave character of the ,christian types is exemplified in his deep colouring1 as well as in other respects4 #aj ,holland might be excepted1 and in ,holland similar causes may have had a similar influence4 #aa ,local colour2 literally1 the blot4 #ab ,zanetti ventures to single out the picture of ,tobit and the ,angel in ,s4 ,marziale as the first example of ,titian's own manner1 and in which a direct imitation of ,giorgione is no longer apparent4 ,in this picture the lights are cool and the blood-tint very effective4 #ac ,meno sfumato1 men focoso4--,storia ,pittorica4 #ad ,la prima cosa che de' colori si perde nelle distante il lustro1 loro minima parte4--,trattato1 p4 #bac2 and elsewhere1 ,i lumi principali in picciol luogo son quelli che in picciola distanza sono i primi che si perdono all' occhio4--p4 #abh4 #ae ,a colossal ,st4 ,christopher1 the usual subject1 is frequently seen occupying the whole height of the external wall of a church4 ,we have here an example of the influence of religion1 such as it was1 even on the style of colouring and practical methods of the art4 ,the mere sight of the image of ,st4 ,christopher1 the type of strength1 was considered sufficient to reinvigorate those who were exhausted by the labours of husbandry4 ,the following is a specimen of the inscriptions inculcating this belief3-- ,christophori ,sancti speciem quicumque tuetur1 ,illo namque die nullo languore tenetur4 ,hence the practice of painting the figure on the outside of churches1 hence its colossal size1 and hence the powerful qualities in colour above described4 ,see ,maniago1 ,storia delle ,belle ,arti ,friulane4 #af ,the authority of ,fuseli sufficiently warrants the application of the term breadth to colour2 he speaks of ,titian's breadth of local tint4 #ag ,zanetti quotes an opinion of the painters of his time to the same effect3--,teneano essi 7alcuni maestri7 per cosa certa1 che in molte opere ,tiziano volesse fingere il lume--quale si vede nell' inclinarsi del sole verso la sera4 ,gli orizzonti assai luminosi dietro le montagne1 le ombre incerte e pi le carnagioni brunette e rosseggianti delle figure1 gl'induceano a creder questo4--,lib4 ii4 ,leonardo da ,vinci observes1 ,quel corpo che si trover in mediocre lume fia in lui poca differenza da' lumi all' ombre4 ,e questo accade sul far della sera--e queste opere sono dolci ed hacci grazia ogni qualit di volto1 c4--p4 #ccf4 ,elsewhere1 ,le ombre fatte dal sole od altri lumi particolari sono senza grazia4--p4 #ceg2 see also p4 #bdg4 #ah ,see ,francesco ,priscianese ,de' ,primi ,principii della ,lingua ,latina1 ,venice1 #aeej4 ,the letter is at the end of the work4 ,it is quoted in ,ticozzi's ,vite de' ,pittori ,vecelli1 ,milan1 #ahag4 #ai ,the works of ,giorgione are extremely rare4 ,the pictures best calculated to give an idea of the glowing manner for which he is celebrated1 are the somewhat early works and several of the altar-pieces of ,titian1 the best specimens of ,palma ,vecchio1 and the portraits of ,sebastian del ,piombo4 #bj ,zanetti and ,lodovico ,dolce mention ,lorenzo ,lotto as an instance of the excess of ,giorgione's style4 ,titian himself sometimes overstepped the mark1 as his biographers confess1 and as appears1 among other instances1 from the head of ,st4 ,peter in the picture 7now in the ,vatican7 in which the celebrated ,st4 ,sebastian is introduced4 ,raphael was criticised by some cardinals for a similar defect4 ,see ,castiglione1 ,il ,cortigiano1 #a4 ii4 ,in the same paragraph to which the present observations refer1 the authority of ,kircher is quoted2 his treatise1 ,ars magna lucis et umbrae1 was published in ,rome in #afdf4 ,in a portrait of ,nicholas ,poussin1 engraved by ,clouet1 the painter is represented holding a book1 which1 from the title and the circumstance of ,poussin having lived in ,rome in ,kircher's time1 ,goethe supposes to be the work in question4 ,the abuse of the principle above alluded to1 is perhaps exemplified in the red half-tints observable in some of ,poussin's figures4 ,the augmentation of colour in subdued light was still more directly taught by ,lomazzo4 ,he composes the half-tints of flesh merely by diminishing the quantity of white1 the proportions of the other colours employed 7for he enters into minute details7 remaining unaltered4 ,see his ,trattato della arte della ,pittura1 ,milan1 #aehd1 p4 #cja4 #ba ,in the ,dresden ,gallery1 a picture attributed to ,titian--at all events a lucid ,venetian picture--hangs next the ,st4 ,george of ,correggio4 ,after looking at the latter1 the ,venetian work appears glassy and unsubstantial1 but on reversing the order of comparison1 the ,correggio may be said to suffer more1 and for a moment its fine transitions of light and shade seem changed to heaviness4 #bb ,the finest works of ,tintoret---the ,crucifixion and the ,miracolo del ,servo 7considered here merely with reference to their colour17 may be said to combine the excellences of ,titian and ,giacomo ,bassan1 on a grand scale2 the sparkling clearness of the latter is one of the prominent characteristics of these pictures4 ,tintoret is reported to have once said that a union of his own knowledge of form with ,bassan's colour would be the perfection of painting4 ,see ,verei ,notizie de' ,pittori di ,bassano2 ,ven4 #agge1 p4 #fa4 #bc ,that this last quality1 the characteristic of ,bassan's best pictures1 was held in high estimation by ,paul ,veronese1 is not only evident from that painter's own works1 but from the circumstance of his preferring to place his sons with ,bassan rather than with any other painter4 7,see ,boschini ,carta del ,navegar1 p4 #bhj47 ,the ,baptism of ,sta4 ,lucilla1 in ,boschini's time considered the finest of ,giacomo's works1 is still in the church of ,s4 ,valentino1 at ,bassano1 and may be considered the type of the lucid and sparkling manner4 ,,note ,f4--,par4 #hc4 ,the author1 in these instances1 seems to be anticipating his subsequent explanations on the effect of semi-transparent mediums4 ,for an explanation of the general view contained in these paragraphs respecting the gradual increase of colour from high light1 see the last ,note4 ,the anonymous ,french work before alluded to1 among other interesting examples1 contains a chapter on shadows cast by the upper light of the sky and coloured by the setting sun4 ,the effect of this remarkable combination is1 that the light on a wall is most coloured immediately under a projecting roof1 and becomes comparatively neutralised in proportion to its distance from the edge of the darkest shade4 ,,note ,g4--,par4 #ih4 ,the simplest case of the phenomenon1 which ,goethe calls a subjective halo1 and one which at once explains its cause1 is the following4 ,regard a red wafer on a sheet of white paper1 keeping the eye stedfastly fixed on a point at its center4 ,when the retina is fatigued1 withdraw the head a little from the paper1 and a green halo will appear to surround the wafer4 ,by this slight increase of distance the image of the wafer itself on the retina becomes smaller1 and the ocular spectrum which before coincided with the direct image1 being now relatively larger1 is seen as a surrounding ring4--,s4 ,f4 ,goethe mentions cases of this kind1 but does not class them with subjective halos4 ,see ,par4 #cj4 ,,note ,h4--,par4 #aac4 ,cases of this kind are by no means uncommon4 ,several interesting ones are related in ,sir ,john ,herschell's article on ,light in the ,encyclopdia ,metropolitana4 ,careful investigation has1 however1 shown that this defect of vision arises in most1 if not in all cases1 from an inability to perceive the red1 not the blue rays4 ,the terms are so confounded by the individuals thus affected1 that the comparison of colours in their presence is the only criterion4--,s4 ,f4 ,,note ,i4--,par4 #ace4 ,the author more than once admits that this chapter on ,pathological ,colours is very incomplete1 and expresses a wish 7,par4 #gcd7 that some medical physiologists would investigate the subject further4 ,this was afterwards in a great degree accomplished by ,dr4 ,johannes ,mller1 in his memoir ber die ,phantastischen ,gesichtserscheinungen4 ,coblentz1 #ahbf4 ,similar phenomena have been also investigated with great labour and success by ,purkinje4 ,for a collection of extraordinary facts of the kind recorded by these writers1 the reader may consult ,scott's ,letters on ,demonology and ,witchcraft4#a ,the instances adduced by ,mller and others are1 however1 intended to prove the inherent capacity of the organ of vision to produce light and colours4 ,in some maladies of the eye1 the patient1 it seems1 suffers the constant presence of light without external light4 ,the exciting principle in this case is thus proved to be within1 and the conclusion of the physiologists is that external light is only one of the causes which produce luminous and coloured impressions4 ,that this view was anticipated by ,newton may be gathered from the concluding query in the third book of his ,optics4 #a ,see also a curious passage on the beatific vision of the monks of ,mount ,athos1 in ,gibbon1 chap4 #fc4 ,,note ,k4--,par4 #adj4 ,catoptrical colours4 ,the colours included under this head are principally those of fibres and grooved surfaces2 they can be produced artificially by cutting parallel grooves on a surface of metal from #bjjj to #aj1jjj in the inch4 ,see ',brewster's ,optics1' p4 #abj4 ,the colours called by ,goethe paroptical1 correspond with those produced by the diffraction or inflection of light in the received theory4--,see ,brewster1 p4 #ie4 ,the phenomena included under the title ',epoptical ,colours1' are generally known as the colours of thin plates4 ,they vary with the thickness of the film1 and the colour seen by reflection always differs from that seen by transmission4 ,the laws of these phenomena have been thoroughly investigated4 ,see ,nobili1 and ,brewster1 p4 #ajj4--,s4 ,f4 ,the colours produced by the transmission of polarised light through chrystalised mediums1 were described by ,goethe1 in his mode1 subsequently to the publication of his general theory1 under the name of ,entoptic ,colours4 ,see note to ,par4 #dhe4 ,,note ,l4--,par4 #aej4 ,we have in this and the next paragraph the outline of ,goethe's system4 ,the examples that follow seem to establish the doctrine here laid down1 but there are many cases which it appears cannot be explained on such principles3 hence1 philosophers generally prefer the theory of absorption1 according to which it appears that certain mediums have the property of absorbing some of the component rays of white light1 while they allow the passage of others4#a ,whether all the facts adduced by ,goethe--for instance1 that recorded in ,par4 #agb1 are to be explained by this doctrine1 we leave to the investigators of nature to determine4 ,dr4 ,eckermann1 in conversing with ,goethe1 thus described the two leading phenomena 7#aef1 #aeh7 as seen by him in the ,alps4 ,at a distance of eighteen or twenty miles at mid-day in bright sunshine1 the snow appeared yellow or even reddish1 while the dark parts of the mountain1 free from snow1 were of the most decided blue4 ,the appearances did not surprise me1 for ,i could have predicted that the mass of the interposed medium would give a deep yellow tone to the white snow1 but ,i was pleased to witness the effect1 since it so entirely contradicted the erroneous views of some philosophers1 who assert that the air has a blue-tinging quality4 ,the observation1 said ,goethe1 is of importance1 and contradicts the error you allude to completely4#b ,the same writer has some observations to the same effect on the colour of the ,rhone at ,geneva4 ,a circumstance of an amusing nature which he relates in confirmation of ,goethe's theory1 deserves to be inserted4 ,here 7at ,strasburg71 passing by a shop1 ,i saw a little glass bust of ,napoleon1 which1 relieved as it was against the dark interior of the room1 exhibited every gradation of blue1 from milky light blue to deep violet4 ,i foresaw that the bust seen from within the shop with the light behind it1 would present every degree of yellow1 and ,i could not resist walking in and addressing the owner1 though perfectly unknown to me4 ,my first glance was directed to the bust1 in which1 to my great joy1 ,i saw at once the most brilliant colours of the warmer kind1 from the palest yellow to dark ruby red4 ,i eagerly asked if ,i might be allowed to purchase the bust2 the owner replied that he had only lately brought it with him from ,paris1 from a similar attachment to the emperor to that which ,i appeared to feel1 but1 as my ardour seemed far to surpass his1 ,i deserved to possess it4 ,so invaluable did this treasure seem in my eyes1 that ,i could not help looking at the good man with wonder as he put the bust into my hands for a few franks4 ,i sent it1 together with a curious medal which ,i had bought in ,milan1 as a present to ,goethe1 and when at ,frankfort received the following letter from him4 ,the letter1 which ,dr4 ,eckermann gives entire1 thus concludes--,when you return to ,weimar you shall see the bust in bright sunshine1 and while the transparent countenance exhibits a quiet blue1#c the thick mass of the breast and epaulettes glows with every gradation of warmth1 from the most powerful ruby-red downwards2 and as the granite statue of ,memnon uttered harmonious sounds1 so the dim glass image displays itself in the pomp of colours4 ,the hero is victorious still in supporting the ,farbenlehre4#d ,one effect of ,goethe's theory has been to invite the attention of scientific men to facts and appearances which had before been unnoticed or unexplained4 ,to the above cases may be added the very common1 but very important1 fact in painting1 that a light warm colour1 passed in a semi-transparent state over a dark one1 produces a cold1 bluish hue1 while the operation reversed1 produces extreme warmth4 ,on the judicious application of both these effects1 but especially of the latter1 the richness and brilliancy of the best-coloured pictures greatly depends4 ,the principle is to be recognised in the productions of schools apparently opposite in their methods4 ,thus the practice of leaving the ground1 through which a light colour is apparent1 as a means of ensuring warmth and depth1 is very common among the ,dutch and ,flemish painters4 ,the ,italians1 again1 who preferred a solid under-painting1 speak of internal light as the most fascinating quality in colour4 ,when the ground is entirely covered by solid painting1 as in the works of some colourists1 the warmest tints in shadows and reflections have been found necessary to represent it4 ,this was the practice of ,rembrandt frequently1 and of ,reynolds universally1 but the glow of their general colour is still owing to its being repeatedly or ultimately enriched on the above principle4 ,lastly1 the works of those masters who were accustomed to paint on dark grounds are often heavy and opaque2 and even where this influence of the ground was overcome1 the effects of time must be constantly diminishing the warmth of their colouring as the surface becomes rubbed and the dark ground more apparent through it4 ,the practice of painting on dark grounds was intended by the ,carracci to compel the students of their school to aim at the direct imitation of the model1 and to acquire the use of the brush2 for the dark ground could only be overcome by very solid painting4 ,the result answered their expectations as far as dexterity of pencil was concerned1 but the method was fatal to brilliancy of colour4 ,an intelligent writer of the seventeenth century#e relates that ,guido adopted his extremely light style from seeing the rapid change in some works of the ,carracci soon after they were done4 ,it is important1 however1 to remark1 that ,guido's remedy was external rather than internal brilliancy2 and it is evident that so powerless a brightness as white paint can only acquire the splendour of light by great contrast1 and1 above all1 by being seen through external darkness4 ,the secret of ,van ,eyck and his contemporaries is always assumed to consist in the vehicle 7varnish or oils7 he employed2 but a far more important condition of the splendour of colour in the works of those masters was the careful preservation of internal light by painting thinly1 but ultimately with great force1 on white grounds4 ,in some of the early ,flemish pictures in the ,royal ,gallery at ,munich1 it may be observed1 that wherever an alteration was made by the painter1 so that a light colour is painted over a dark one1 the colour is as opaque as in any of the more modern pictures which are generally contrasted with such works4 ,no quality in the vehicle could prevent this opacity under such circumstances2 and on the other hand1 provided the internal splendour is by any means preserved1 the vehicle is comparatively unimportant4 ,it matters not 7say the authorities on these points7 whether the effect in question is attained by painting thinly over the ground1 in the manner of the early ,flemish painters and sometimes of ,rubens1 or by painting a solid light preparation to be afterwards toned to richness in the manner of the ,venetians4 ,among the mechanical causes of the clearness of colours superposed on a light preparation may be mentioned that of careful grinding4 ,all writers on art who have descended to practical details have insisted on this4 ,from the appearance of some ,venetian pictures it may be conjectured that the colours of the solid under-painting were sometimes less perfectly ground than the scumbling colours 7the light having to pass through the one and to be reflected from the other74 ,the ,flemish painters appear to have used carefully-ground pigments universally4 ,this is very evident in ,flemish copies from ,raphael1 which1 though equally impasted with the originals1 are to be detected1 among other indications1 by the finely-ground colours employed4 #a ,see ,mller's ,elements of ,physiology1 translated from the ,german by ,william ,baly1 ,m4,d4 ,the laws of absorption1 it has been observed1 have not been studied with so much success as those of other phenomena of physical optics1 but some excellent observations on the subject will be found in ,herschell's ,treatise on ,light in the ,encyclopdia ,metropolitana1 ,,iii4 #b ,eckermann's ,gesprche mit ,goethe1 vol4 ii4 p4 #bhj4 ,leonardo da ,vinci had made precisely the same observation4 ,a distant mountain will appear of a more beautiful blue in proportion as it is dark in colour4 ,the illumined air1 interposed between the eye and the dark mass1 being thinner towards the summit of the mountain1 will exhibit the darkness as a deeper blue and vice vers4--,trattato della ,pittura1 p4 #adc4 ,elsewhere--,the air which intervenes between the eye and dark mountains becomes blue2 but it does not become blue in 7before7 the light part1 and much less in 7before7 the portion that is covered with snow4--p4 #bdd4 #c ,this supposes either that the mass was considerably thicker1 or that there was a dark ground behind the head1 and a light ground behind the rest of the figure4 #d ,eckermann's ,gesprche mit ,goethe1 vol4 ii4 p4 #bdb4 #e ,scanelli1 ,microcosmo della ,pittura1 ,cesena1 #afeg1 p4 #aad4 ,,note ,m4--,par4 #agg4 ,without entering further into the scientific merits or demerits of this chapter on the ,first ,class of ,dioptrical ,colours1 it is to be observed that several of the examples correspond with the observations of ,leonardo da ,vinci1 and again with those of a much older authority1 namely1 ,aristotle4 ,goethe himself admits1 and it has been remarked by others1 that his theory1 in many respects1 closely resembles that of ,aristotle3 indeed he confesses#a that at one time he had an intention of merely paraphrasing that philosopher's ,treatise on ,colours4#b ,we have already remarked 7,note on par4 #aej7 that ,goethe's notion with regard to the production of warm colours1 by the interposition of dark transparent mediums before a light ground1 agrees with the practice of the best schools in colouring2 and it is not impossible that the same reasons which may make this part of the doctrine generally acceptable to artists now1 may have recommended the very similar theory of ,aristotle to the painters of the fifteenth and sixteenth centuries3 at all events1 it appears that the ancient theory was known to those painters4 ,it is unnecessary to dwell on the fact that the doctrines of ,aristotle were enthusiastically embraced and generally inculcated at the period in question2#c but it has not been observed that the ,italian writers who translated1 paraphrased1 and commented on ,aristotle's ,treatise on ,colours in particular1 were in several instances the personal friends of distinguished painters4 ,celio ,calcagnini#d had the highest admiration for ,raphael2 ,lodovico ,dolce#e was the eulogist of ,titian2 ,portius1#f whose amicable relations with the ,florentine painters may be inferred from various circumstances1 lectured at ,florence on the ,aristotelian doctrines early in the sixteenth century4 ,the ,italian translations were later1 but still prove that these studies were undertaken with reference to the arts1 for one of them is dedicated to the painter ,cigoli4#g ,the writers on art1 from ,leon ,battista ,alberti to ,borghini1 without mentioning later authorities1 either tacitly coincide with the ,aristotelian doctrine1 or openly profess to explain it4 ,it is true this is not always done in the clearest manner1 and some of these writers might say with ,lodovico ,dolce1 ,i speak of colours1 not as a painter1 for that would be the province of the divine ,titian4 ,leonardo da ,vinci in his writings1 as in everything else1 appears as an original genius4 ,he now and then alludes generally to opinions of philosophers1 but he quotes no authority ancient or modern4 ,nevertheless1 a passage on the nature of colours1 particularly where he speaks of the colours of the elements1 appears to be copied from ,leon ,battista ,alberti1#h and from the mode in which some of ,leonardo's propositions are stated1 it has been supposed#i that he had been accustomed at ,florence to the form of the ,aristotelian philosophy4 ,at all events1 some of the most important of his observations respecting light and colours1 have a great analogy with those contained in the treatise in question4 ,the following examples will be sufficient to prove this coincidence2 the corresponding passages in ,goethe are indicated1 as usual1 by the numbers of the paragraphs2 the references to ,leonardo's treatise are given at the bottom of the page4 ,aristotle4 ,a vivid and brilliant red appears when the weak rays of the sun are tempered by subdued and shadowy white1--#aed4 ,leonardo ,the air which is between the sun and the earth at sun-rise or sun-set1 always invests what is beyond it more than any other 7higher7 portion of the air3 this is because it is whiter4#aj ,a bright object loses its whiteness in proportion to its distance from the eye much more when it is illuminated by the sun1 for it partakes of the colour of the sun mingled with the colour 7tempered by the mass7 of the air interposed between the eye and the brightness4#aa ,aristotle4 ,if light is overspread with much obscurity1 a red colour appears2 if the light is brilliant and vivid1 this red changes to a flame-colour4#ab--aej1 #afj4 ,leonardo4 ,this 7the effect of transparent colours on various grounds7 is evident in smoke1 which is blue when seen against black1 but when it is opposed to the 7light7 blue sky1 it appears brownish and reddening4#ac ,aristotle4 ,white surfaces as a ground for colours1 have the effect of making the pigments#ad appear in greater splendour4--#eid1 #ijb4 ,leonardo4 ,to exhibit colours in their beauty1 the whitest ground should be prepared4 ,i speak of colours that are 7more or less7 transparent4#ae ,aristotle4 ,the air near us appears colourless2 but when seen in depth1 owing to its thinness it appears blue2#af for where the light is deficient 7beyond it71 the air is affected by the darkness and appears blue3 in a very accumulated state1 however1 it appears1 as is the case with water1 quite white4--#aee1 #aeh4 ,leonardo4 ,the blue of the atmosphere is owing to the mass of illuminated air interposed between the darkness above and the earth4 ,the air in itself has no colour1 but assumes qualities according to the nature of the objects which are beyond it4 ,the blue of the atmosphere will be the more intense in proportion to the degree of darkness beyond it3 elsewhere--if the air had not darkness beyond it1 it would be white4#ag ,aristotle4 ,we see no colour in its pure state1 but every hue is variously intermingled with others3 even when it is uninfluenced by other colours1 the effect of light and shade modifies it in various ways1 so that it undergoes alterations and appears unlike itself4 ,thus1 bodies seen in shade or in light1 in more pronounced or softer sun-shine1 with their surfaces inclined this way or that1 with every change exhibit a different colour4 ,leonardo4 ,no substance will ever exhibit its own hue unless the light which illumines it is entirely similar in colour4 ,it very rarely happens that the shadows of opaque bodies are really similar 7in colour7 to the illumined parts4 ,the surface of every substance partakes of as many hues as are reflected from surrounding objects4#ah ,aristotle4 ,so1 again1 with regard to the light of fire1 of the moon1 or of lamps1 each has a different colour1 which is variously combined with differently coloured objects4 ,leonardo4 ,we can scarcely ever say that the surface of illumined bodies exhibits the real colour of those bodies4 ,take a white band and place it in the dark1 and let it receive light by means of three apertures from the sun1 from fire1 and from the sky3 the white band will be tricoloured4#ai ,aristotle4 ,when the light falls on any object and assumes 7for example7 a red or green tint1 it is again reflected on other substances1 thus undergoing a new change4 ,but this effect1 though it really takes place1 is not appreciable by the eye3 though the light thus reflected to the eye is composed of a variety of colours1 the principal of these only are distinguishable4 ,leonardo4 ,no colour reflected on the surface of another colour1 tinges that surface with its own colour 7merely71 but will be mixed with various other reflections impinging on the same surface3 but such effects1 he observes elsewhere1 are scarcely1 if at all1 distinguishable in a very diffused light4#bj ,aristotle4 ,thus1 all combinations of colours are owing to three causes3 the light1 the medium through which the light appears1 such as water or air1 and lastly the local colour from which the light happens to be reflected4 ,leonardo4 ,all illumined objects partake of the colour of the light they receive4 ,every opaque surface partakes of the colour of the intervening transparent medium1 according to the density of such medium and the distance between the eye and the object4 ,the medium is of two kinds2 either it has a surface1 like water1 c41 or it is without a common surface1 like the air4#ba ,in the observations on trees and plants more points of resemblance might be quoted2 the passages corresponding with ,goethe's views are much more numerous4 ,it is remarkable that ,leonardo1 in opposition1 it seems to some authorities1#bb agrees with ,aristotle in reckoning black and white as colours1 placing them at the beginning and end of the scale4#bc ,like ,aristotle1 again1 he frequently makes use of the term black1 for obscurity2 he even goes further1 for he seems to consider that blue may be produced by the actual mixture of black and white1 provided they are pure4#bd ,the ancient author1 however1 explains himself on this point as follows--,we must not attempt to make our observations on these effects by mixing colours as painters mix them1 but by remarking the appearances as produced by the rays of light mingling with each other4#be ,when we consider that ,leonardo's ,treatise professes to embrace the subject of imitation in painting1 and that ,aristotle's briefly examines the physical nature and appearance of colours1 it must be admitted that the latter sustains the above comparison with advantage2 and it is somewhat extraordinary that observations indicating so refined a knowledge of nature1 as regards the picturesque1 should not have been taken into the account1 for such appears to be the fact1 in the various opinions and conjectures that have been expressed from time to time on the painting of the ,greeks4 ,the treatise in question must have been written when ,apelles painted1 or immediately before2 and as a proof that ,aristotle's remarks on the effect of semi-transparent mediums were not lost on the artists of his time1 the following passage from ,pliny is subjoined1 for1 though it is well known1 it acquires additional interest from the foregoing extracts4 ,he 7,apelles7 passed a dark colour over his pictures when finished1 so thin that it increased the splendour of the tints1 while it protected the surface from dust and dirt3 it could only be seen on looking into the picture4 ,the effect of this operation1 judiciously managed1 was to prevent the colours from being too glaring1 and to give the spectator the impression of looking through a transparent crystal4 ,at the same time it seemed almost imperceptibly to add a certain dignity of tone to colours that were too florid4 ,this1 says ,reynolds1 is a true and artist-like description of glazing or scumbling1 such as was practised by ,titian and the rest of the ,venetian painters4 ,the account of ,pliny has1 in this instance1 internal evidence of truth1 but it is fully confirmed by the following passage in ,aristotle3--,another mode in which the effect of colours is exhibited is when they appear through each other1 as painters employ them when they glaze 77#bf a 7dark7 colour over a lighter one2 just as the sun1 which is in itself white1 assumes a red colour when seen through darkness and smoke4 ,this operation also ensures a variety of colours1 for there will be a certain ratio between those which are on the surface and those which are in depth4--,de ,sensu et ,sensili4 ,aristotle's notion respecting the derivation of colours from white and black may perhaps be illustrated by the following opinion on the very similar theory of ,goethe4 ,goethe and ,seebeck regard colour as resulting from the mixture of white and black1 and ascribe to the different colours a quality of darkness 771 by the different degrees of which they are distinguished1 passing from white to black through the gradations of yellow1 orange1 red1 violet1 and blue1 while green appears to be intermediate again between yellow and blue4 ,this remark1 though it has no influence in weakening the theory of colours proposed by ,newton1 is certainly correct1 having been confirmed experimentally by the researches of ,herschell1 who ascertained the relative intensity of the different coloured rays by illuminating objects under the microscope by their means1 c4 ,another certain proof of the difference in brightness of the different coloured rays is afforded by the phenomena of ocular spectra4 ,if1 after gazing at the sun1 the eyes are closed so as to exclude the light1 the image of the sun appears at first as a luminous or white spectrum upon a dark ground1 but it gradually passes through the series of colours to black1 that is to say1 until it can no longer be distinguished from the dark field of vision2 and the colours which it assumes are successively those intermediate between white and black in the order of their illuminating power or brightness1 namely1 yellow1 orange1 red1 violet1 and blue4 ,if1 on the other hand1 after looking for some time at the sun we turn our eyes towards a white surface1 the image of the sun is seen at first as a black spectrum upon the white surface1 and gradually passes through the different colours from the darkest to the lightest1 and at last becomes white1 so that it can no longer be distinguished from the white surface#bg--,see par #dj1 #dd4 ,it is not impossible that ,aristotle's enumeration of the colours may have been derived from1 or confirmed by1 this very experiment4 ,speaking of the after-image of colours he says1 ,the impression not only exists in the sensorium in the act of perceiving1 but remains when the organ is at rest4 ,thus if we look long and intently on any object1 when we change the direction of the eyes a responding colour follows4 ,if we look at the sun1 or any other very bright object1 and afterwards shut our eyes1 we shall1 as if in ordinary vision1 first see a colour of the same kind2 this will presently be changed to a red colour1 then to purple1 and so on till it ends in black and disappears4--,de ,insomniis4 #a ,geschichte der ,farbenlehre1 in the ,nachgelassene ,werke4 ,cotta1 #ahcc4 #b ,the treatise in question is ascribed by ,goethe to ,theophrastus1 but it is included in most editions of ,aristotle1 and even attributed to him in those which contain the works of both philosophers2 for instance1 in the ,aldine ,princeps edition1 #adif4 ,calcagnini says1 the treatise is made up of two separate works on the subject1 both by ,aristotle4 #c ,his authority seems to have been equally great on subjects connected with the phenomena of vision2 the ,italian translator of a ,latin treatise1 by ,portius1 on the structure and colours of the eye1 thus opens his dedication to the ,cardinal ,ercole ,gonzaga1 of ,mantua3--,grande anzi quasi infinito l'obligo che ha il mondo con quel pi divino che umano spirito di ,aristotile4 #d ,in a letter to ,ziegler the mathematician1 ,calcagnini speaks of ,raphael as the first of painters in the theory as well as in the practice of his art4 ,this expression may1 however1 have had reference to a remarkable circumstance mentioned in the same letter1 namely1 that ,raphael entertained the learned ,fabius of ,ravenna as a constant guest1 and employed him to translate ,vitruvius into ,italian4 ,this ,,ms4 translation1 with marginal notes1 written by ,raphael1 is now in the library at ,munich4 ,passavant1 ,rafael von ,urbino4 #e ,lodovico ,dolce's ,treatise on ,colours 7#aefe7 is in the form of a dialogue1 like his ,aretino4 ,the abridged theory of ,aristotle is followed by a translation of the ,treatise of ,antonius ,thylesius on ,colours2 this is adapted to the same colloquial form1 and the author is not acknowledged3 the book ends with an absurd catalogue of emblems4 ,the ,somma della ,filosofia d',aristotile1 published earlier by the same author1 is a very careless performance4 #f ,a ,latin translation of ,aristotle's ,treatise on ,colours1 with comments by ,simon ,portius1 was first published1 according to ,goethe1 at ,naples in #aecg4 ,in a later ,florentine edition1 #aedh1 dedicated to ,cosmo ,i41 ,portius alludes to his having lectured at an earlier period in ,florence on the doctrines of ,aristotle1 at which time he translated the treatise in question4 ,another ,latin translation1 with notes1 was published later in the same century at ,padua--,emanuele ,marguino ,interprete3 but by far the clearest view of the ,aristotelian theory is to be found in the treatise of ,antonio ,vidi ,scarmiglione of ,fuligno 7,de ,coloribus1 ,marpurgi1 #aeia74 ,it is dedicated to the ,emperor ,rudolph ,,ii4 ,of all the paraphrases of the ancient doctrine this comes nearest to the system of ,goethe2 but neither this nor any other of the works alluded to throughout this ,note are mentioned by the author in his ,history of the ,doctrine of ,colours1 except that of ,portius4 #g ,an earlier ,italian translation appeared in ,rome1 #aece4 ,see ,argelatus ,biblioteca degli ,volgarizzatori4 #h ,della ,pittura e della ,statua1 ,lib4 ,i1 p4 #af1 ,milan edition1 #ahjd4 ,compare with the ,trattato della ,pittura1 p4 #ada4 ,other points of resemblance are to be met with4 ,the notion of certain colours appropriated to the four elements1 occurs in ,aristotle1 and is indeed attributed to older writers4 #i ,see the notes to the ,roman edition of the ,trattato della ,pittura4 #aj ,page #bcg4 #aa ,page #cja4 #ab ,in the ,treatise ,de ,igne1 by ,theophrastus1 we find the same notion thus expressed3 ,brightness 7 7 seen through a dark coloured medium 7 7 appears red2 as the sun seen through smoke or soot3 hence the coal is redder than the flame4 ,scarmiglione1 from whom ,kircher seems to have copied1 observes3--,itaque color realis est lux opaca2 licet id e plurimis apparentiis colligere4 ,luna enim in magn solis eclipsi rubra conspicitur1 quia tenebris lux prpeditur ac veluti tegitur4--,de ,coloribus4 #ac ,page #abb4 #ad 3 translated flores by ,calcagnini and the rest1 by ,goethe1 die ,blthe1 the bloom4 ,that the word sometimes signified pigments is sufficiently apparent from the following passage of ,suidas 7quoted by ,emeric ,david1 ,discours ,historiques sur la ,peinture ,moderne7 1 4 ,variis pigmentis ornat1 ut ceruss1 fuco1 et aliis similibus4 7,suid4 in voc4 47 ,a panel prepared for painting1 with a white ground consolidated with wax1 and perhaps mastic1 was found in ,herculaneum4 #ae ,page #aad4 #af 4 ,but when seen in depth1 it appears 7even7 in its nearest colour1 blue1 owing to its thinness4 ,the ,latin interpretations vary very much throughout4 ,the point which is chiefly important is however plain enough1 viz4 that darkness seen through a light medium is blue4 #ag ,page #acf-dcj4 #ah ,page #aba1 #cjf1 #cbf1 #chg4 #ai ,page #cjf4 #bj ,page #ajd1 #cfi4 #ba ,page #bcf1 #bfj1 #cbh4 #bb ,de' semplici colori il primo il bianco3 beuch i filosofi non accettano n il bianco n il nero nel numero de' colori4--p4 #abe1 #ada4 ,elsewhere1 however1 he sometimes adopts the received opinion4 #bc ,leon ,battista ,alberti1 in like manner observes3--,affermano 7i filosofi7 che le spezie de' colori sono sette1 cio1 che il bianco ed il nero sono i duoi estremi1 infra i quali ve n' uno nel mezzo 7rosso7 e che infra ciascuno di questi duoi estremi e quel del mezzo1 da ogni parte ve ne sono due altri4 ,an absurd statement of ,lomazzo1 p4 #aij1 is copied verbatim from ,lodovico ,dolce 7,somma della ,filos4 d',arist472 but elsewhere1 p4 #cjf1 ,lomazzo agrees with ,alberti4 ,aristotle seems to have misled the two first1 for after saying there are seven colours1 he appears only to mention six3 he says--,there are seven colours1 if brown is to be considered equivalent to black1 which seems reasonable4 ,yellow1 again1 may be said to be a modification of white4 ,between these we find red1 purple1 green1 and blue4--,de ,sensu et ,sensili4 ,perhaps it is in accordance with this passage that ,leonardo da ,vinci reckons eight colours4--,trattato1 p4 #abf4 #bd ,page #abb1 #adb1 #bcg4 #be ,on the authority of this explanation the word has sometimes been translated in the foregoing extracts obscurity1 darkness4 ,raffaello ,borghini1 in his attempt to describe the doctrine of ,aristotle with a view to painting1 observes--,there are two principles which concur in the production of colour1 namely1 light and transparence4 ,but he soon loses this clue to the best part of the ancient theory1 and when he has to speak of the derivation of colours from white and black1 he evidently understands it in a mere atomic sense1 and adds--,i shall not at present pursue the opinion of ,aristotle1 who assumes black and white as principal colours1 and considers all the rest as intermediate between them4--,il ,riposo1 #a4 ii4 ,accordingly1 like ,lodovico ,dolce1 he proceeds to a subject where he was more at home1 namely1 the symbolical meaning of colours4 #bf ,this word is only strictly applied to unctuous substances1 and may confirm the views of those writers who have conjectured that asphaltum was a chief ingredient in the atramentum of the ancients4 #bg ,elements of ,physiology1 by ,j4 ,mller1 ,m4,d41 translated from the ,german by ,william ,baly1 ,m4,d4 ,london1 #ahci4 ,,note ,n4--,par4 #bdf4 ,the appearance of white in the centre1 according to the ,newtonian theory1 arises from each line of rays forming its own spectrum4 ,these spectra1 superposing each other on all the middle part1 leave uncorrected 7unneutralised7 colours only at the two edges4--,s4 ,f4#a #a ,this was objected to ,goethe when his ,beytrge sur ,optik first appeared2 he answered the objection by a coloured diagram in the plates to the ,farbenlehre3 in this he undertakes to show that the assumed gradual correction of the colours would produce results different from the actual appearance in nature4 ,,note ,o4--,par4 #beb4 ,these experiments with grey objects1 which exhibit different colours as they are on dark or light grounds1 were suggested1 ,goethe tells us1 by an observation of ,antonius ,lucas1 of ,lttich1 one of ,newton's opponents1 and1 in the opinion of the author1 one of the few who made any well-founded objections4 ,lucas remarks1 that the sun acts merely as a circumscribed image in the prismatic experiments1 and that if the same sun had a lighter background than itself1 the colours of the prism would be reversed4 ,thus in ,goethe's experiments1 when the grey disk is on a dark ground1 it is edged with blue on being magnified2 when on a light ground it is edged with yellow4 ,goethe acknowledges that ,lucas had in some measure anticipated his own theory4--,vol4 ii4 p4 #ddj4 ,,note ,p4--,par4 #bhd4 ,the earnestness and pertinacity with which ,goethe insisted that the different colours are not subject to different degrees of refrangibility are at least calculated to prove that he was himself convinced on the subject1 and1 however extraordinary it may seem1 his conviction appears to have been the result of infinite experiments and the fullest ocular evidence4 ,he returns to the question in the controversial division of his work1 in the historical part1 and again in the description of the plates4 ,in the first he endeavours to show that ,newton's experiment with the blue and red paper depends entirely on the colours being so contrived as to appear elongated or curtailed by the prismatic borders4 ,if1 he says1 we take a light-blue instead of a dark one1 the illusion 7in the latter case7 is at once evident4 ,according to the ,newtonian theory the yellow-red 7red7 is the least refrangible colour1 the violet the most refrangible4 ,why1 then1 does ,newton place a blue paper instead of a violet next the red8 ,if the fact were as he states it1 the difference in the refrangibility of the yellow-red and violet would be greater than in the case of the yellow-red and blue4 ,but here comes in the circumstance that a violet paper conceals the prismatic borders less than a dark-blue paper1 as every observer may now easily convince himself1 c4--,polemischer ,theil1 par4 #de4 ,desaguliers1 in repeating the experiment1 confessed that if the ground of the colours was not black1 the effect did not take place so well4 ,goethe adds1 not only not so well1 but not at all4--,historischer ,theil1 p4 #dei4 ,lucas of ,lttich1 one of ,newton's first opponents1 denied that two differently-coloured silks are different in distinctness when seen in the microscope4 ,another experiment proposed by him1 to show the unsoundness of the doctrine of various refrangibility1 was the following3--,let a tin plate painted with the prismatic colours in stripes be placed in an empty cubical vessel1 so that from the spectator's point of view the colours may be just hidden by the rim4 ,on pouring water into this vessel1 all the colours become visible in the same degree2 whereas1 it was contended1 if the ,newtonian doctrine were true1 some colours would be apparent before others4--,historischer ,theil1 p4 #dcd4 ,such are the arguments and experiments adduced by ,goethe on this subject2 they have all probably been answered4 ,in his analysis of ,newton's celebrated ,experimentum ,crucis1 he shows again that by reversing the prismatic colours 7refracting a dark instead of a light object71 the colours that are the most refrangible in ,newton's experiment become the least so1 and vice vers4 ,without reference to this objection1 it is now admitted that the difference of colour is not a test of difference of refrangibility1 and the conclusion deduced by ,newton is no longer admissible as a general truth1 that to the same degree of refrangibility ever belongs the same colour1 and to the same colour ever belongs the same degree of refrangibility4--,brewster's ,optics1 p4 #gb4 ,,note ,q--,par4 #chg4 ,with the exception of two very inconclusive letters to ,sulpice ,boissere1 and some incidental observations in the conclusion of the historical portion under the head of entoptic colours1 ,goethe never returned to the rainbow4 ,among the plates he gave the diagram of ,antonius de ,dominis4 ,an interesting chapter on halos1 parhelia1 and paraselen1 will be found in ,brewster's ,optics1 p4 #bgj4 ,,note ,r4--,par4 #dgh4 ,the most complete exhibition of the colouring or mantling of metals was attained by the late ,cav4 ,nobili1 professor of physical science in ,florence4 ,the general mode in which these colours are produced is thus explained by him3#a-- ,a point of platinum is placed vertically at the distance of about half a line above a lamina of the same metal laid horizontally at the bottom of a vessel of glass or porcelain4 ,into this vessel a solution of acetate of lead is poured so as to cover not only the lamina of platinum1 but two or three lines of the point as well4 ,lastly1 the point is put in communication with the negative pole of a battery1 and the lamina with the positive pole4 ,at the moment in which the circuit is completed a series of coloured rings is produced on the lamina under the point similar to those observed by ,newton in lenses pressed together4 ,the scale of colours thus produced corresponds very nearly with that observed by ,newton and others in thin plates and films1 but it is fuller1 for it extends to forty-four tints4 ,the following list1 as given by ,nobili1 is divided by him into four series to agree with those of ,newton3 the numbers in brackets are those of ,newton's scale4 ,the ,italian terms are untranslated1 because the colours in some cases present very delicate transitions4#b ,first ,series4 #a4 ,biondo argentino 7#d74c #f4 ,fulvo acceso4 #b4 ,biondo4 #g4 ,rosso di rame 7#f74 #c4 ,biondo d'oro4 #h4 ,ocria4 #d4 ,biondo acceso 7#e74 #i4 ,ocria violacea4 #e4 ,fulvo4 #aj4 ,rosso violaceo 7#g74 ,second ,series4 #aa4 ,violetto 7#h74 #bj4 ,giallo acceso4 #ab4 ,indaco 7#aj74 #ba4 ,giallo-rancio4 #ac4 ,blu carico4 #bb4 ,rancio 7#ac74 #ad4 ,blu4 #bc4 ,rancio-rossiccio4 #ae4 ,blu chiaro 7#aa7 #bd4 ,rancio-rosso4 #af4 ,celeste4 #be4 ,rosso-rancio4 #ag4 ,celeste giallognolo4 #bf4 ,lacca-rancia 7#ad74 #ah4 ,giallo chiarissimo 7#ab74 #bg4 ,lacca4 #ai4 ,giallo4 #bh4 ,lacca accesa 7#ae74 ,third ,series4 #bi4 ,lacca-purpurea 7#af74 #cd4 ,verde-giallo 7#bj74 #cj4 ,lacca-turchiniccia 7#ag74 #ce4 ,verde-rancio4 #ca4 ,porpora-verdognola 7#ah74 #cf4 ,rancio-verde 7#ba74 #cb4 ,verde 7#ai74 #cg4 ,rancio-roseo4 #cc4 ,verde giallognolo4 #ch4 ,lacca-rosea 7#bb74 ,fourth ,series4 #ci4 ,lacca-violacea 7#bd74 #dc4 ,verde-giallo rossiccio 7#bh74 #dj4 ,violaceo-verdognolo 7#be74 #dd4 ,lacca-rosea 7#cj74 #da4 ,verde 7#bf74 #db4 ,verde-giallo 7#bg74 ,these tints1 ,professor ,nobili observes1 are disposed according to the order of the thin mantlings which occasion them2 the colour of the thinnest film is numbered #a2 then follow in order those produced by a gradual thickening of the medium4 ,i cannot deceive myself in this arrangement1 for the thin films which produce the colours are all applied with the same electro-chemical process4 ,the battery1 the solution1 the distances1 c41 are always the same2 the only difference is the time the effect is suffered to last4 ,this is a mere instant for the colour of ,no4 #a1 a little longer for ,no4 #b1 and so on1 increasing for the succeeding numbers4 ,other criterions1 however1 are not wanting to ascertain the place to which each tint belongs4 ,the scale differs from that of ,newton1 inasmuch as there is no blue in ,nobili's first series and no green in the second3 green only appears in the third and fourth series4 ,the first series1 says the ,professor1 is remarkable for the fire and metallic appearance of its tints1 the second for clearness and brilliancy1 the third and fourth for force and richness4 ,the fourth1 he observes1 has the qualities of the third in a somewhat lesser degree1 but the two greens are very nearly alike4 ,it is to be observed1 that red and green are the principal ingredients in the third and fourth series1 blue and yellow in the second and first4 #a ,see ,memorie ed ,osservazioni1 edite et inedite del ,cav4 ,professor ,nobili1 ,firenze1 #ahcd4 #b ,the colours in some of the compound terms are in a manner mutually neutralising2 such terms might1 no doubt1 be amended4 #c ,the three first numbers in ,newton's scale are black1 blue1 and white4 ,,note ,s4--,par4 #dhe4 ,a chapter on entoptic colours1 contained in the supplement to ,goethe's works1 was translated with the intention of inserting it among the notes1 but on the whole it was thought most advisable to omit it4 ,like many other parts of the ,doctrine of ,colours it might have served as a specimen of what may be achieved by accurate observation unassisted by a mathematical foundation4 ,the whole theory of the polarization of light has1 however1 been so fully investigated since ,goethe's time1 that the chapter in question would probably have been found to contain very little to interest scientific readers1 for whom it seems chiefly to have been intended4 ,one observation occurs in it which indeed has more reference to the arts2 in order to make this intelligible1 the leading experiment must be first described1 and for this purpose the following extracts may serve4 #c4a ,the experiment1 in its simplest form1 is to be made as follows3--let a tolerably thick piece of plate-glass be cut into several squares of an inch and a half2 let these be heated to a red heat and then suddenly cooled4 ,the squares of glass which do not split in this operation are now fit to produce the entoptic colours4 #d4 ,in our mode of exhibiting the phenomenon1 the observer is1 above all1 to betake himself1 with his apparatus to the open air4 ,all dark rooms1 all small apertures 7foramina exigua71#b are again to be given up4 ,a pure1 cloudless sky is the source whence we are derive a satisfactory insight into the appearances4 #e4 ,the atmosphere being clear1 let the observer lay the squares above described on a black surface1 so placing them that two sides may be parallel with the plane of vision4 ,when the sun is low1 let him hold the squares so as to reflect to the eye that portion of the sky opposite to the sun1 and he will then perceive four dark points in the four corners of a light space4 ,if1 after this1 he turn towards the quarters of the sky at right angles with that where his first observation was made1 he will see four bright points on a dark ground3 between the two regions the figures appear to fluctuate4 #f4 ,from this simple reflection we now proceed to another1 which1 but little more complicated1 exhibits the appearance much more distinctly4 ,a solid cube of glass1 or in its stead a cube composed of several plates1 is placed on a black mirror1 or held a little inclined above it1 at sun-rise or sun-set4 ,the reflection of the sky being now suffered to fall through the cube on the mirror1 the appearance above described will appear more distinctly4 ,the reflection of the sky opposite to the sun presents four dark points on a light ground2 the two lateral portions of the sky present the contrary appearance1 namely1 four light points on a dark ground4 ,the space not occupied by the corner points appears in the first case as a white cross1 in the other as a black cross1 expressions hereafter employed in describing the phenomena4 ,before sun-rise or after sun-set1 in a very subdued light1 the white cross appears on the side of the sun also4#c ,we thus conclude that the direct reflection of the sun produces a light figure1 which we call a white cross2 the oblique reflection gives a dark figure1 which we call a black cross4 ,if we make the experiment all round the sky1 we shall find that a fluctuation takes place in the intermediate regions4 ,we pass over a variety of observations on the modes of exhibiting this phenomenon1 the natural transparent substances which exhibit it best1 and the detail of the colours seen within#d them1 and proceed to an instance where the author was enabled to distinguish the direct from the oblique reflection by means of the entoptic apparatus1 in a painter's study4 #dj4 ,an excellent artist1 unfortunately too soon taken from us1 ,ferdinand ,jagemann1 who1 with other qualifications1 had a fine eye for light and shade1 colour and keeping1 had built himself a painting-room for large as well as small works4 ,the single high window was to the north1 facing the most open sky1 and it was thought that all necessary requisites had been sufficiently attended to4 ,but after our friend had worked for some time1 it appeared to him1 in painting portraits1 that the faces he copied were not equally well lighted at all hours of the day1 and yet his sitters always occupied the same place1 and the serenity of the atmosphere was unaltered4 ,the variations of the favourable and unfavourable light had their periods during the day4 ,early in the morning the light appeared most unpleasantly grey and unsatisfactory2 it became better1 till at last1 about an hour before noon1 the objects had acquired a totally different appearance4 ,everything presented itself to the eye of the artist in its greatest perfection1 as he would most wish to transfer it to canvas4 ,in the afternoon this beautiful appearance vanished--the light became worse1 even in the brightest day1 without any change having taken place in the atmosphere4 ,as soon as ,i heard of this circumstance1 ,i at once connected it in my own mind with the phenomena which ,i had been so long observing1 and hastened to prove1 by a physical experiment1 what a clear-sighted artist had discovered entirely of himself1 to his own surprise and astonishment4 ,i had the second#e entoptic apparatus brought to the spot1 and the effect on this was what might be conjectured from the above statement4 ,at mid-day1 when the artist saw his model best lighted1 the north1 direct reflection gave the white cross2 in the morning and evening1 on the other hand1 when the unfavourable oblique light was so unpleasant to him1 the cube showed the black cross2 in the intermediate hours the state of transition was apparent4 ,the author proceeds to recall to his memory instances where works of art had struck him by the beauty of their appearance owing to the light coming from the quarter opposite the sun1 in direct reflection1 and adds1 ,since these decided effects are thus traceable to their cause1 the friends of art1 in looking at and exhibiting pictures1 may enhance the enjoyment to themselves and others by attending to a fortunate reflection4 #a ,the numbers1 as usual1 indicate the corresponding paragraphs in the original4 #b ,in the historical part1 ,goethe has to speak of so many followers of ,newton who begin their statements with ,si per foramen exiguum1 that the term is a sort of by-word with him4 #c ,at mid-day on the #bdth of ,june the author observed the white cross reflected from every part of the horizon4 ,at a certain distance from the sun1 corresponding1 he supposes1 with the extent of halos1 the black cross appeared4 #d ,whence the term entoptic4 #e ,before described3 the author describes several others more or less complicated1 and suggests a portable one4 ,such plates1 which need only be an inch and a quarter square1 placed on each other to form a cube1 might be set in a brass case1 open above and below4 ,at one end of this case a black mirror with a hinge1 acting like a cover1 might be fastened4 ,we recommend this simple apparatus1 with which the principal and original experiment may be readily made4 ,with this we could1 in the longest days1 better define the circle round the sun where the black cross appears1 c4 ,,note ,t4--,par4 #dif4 ,since ,goethe wrote1 all the earths have been decomposed1 and have been shown to be metallic bases united with oxygen2 but this does not invalidate his statement4--,s4 ,f4 ,,note ,u4--,par4 #ejb4 ,the cold nature of black and its affinity to blue are assumed by the author throughout2 if the quality is opaque1 and consequently greyish1 such an affinity is obvious1 but in many fine pictures1 intense black seems to be considered as the last effect of heat1 and in accompanying crimson and orange may be said rather to present a difference of degree than a difference of kind4 ,in looking at the great picture of the globe1 we find this last result produced in climates where the sun has greatest power1 as we find it the immediate effect of fire4 ,the light parts of black animals are often of a mellow colour2 the spots and stripes on skins and shells are generally surrounded by a warm hue1 and are brown before they are absolutely black4 ,in combustion1 the blackness which announces the complete ignition1 is preceded always by the same mellow1 orange colour4 ,the representation of this process was probably intended by the ,greeks in the black and subdued orange of their vases3 indeed1 the very colours may have been first produced in the kiln4 ,but without supposing that they were retained merely from this accident1 the fact that the combination itself is extremely harmonious1 would be sufficient to account for its adoption4 ,many of the remarks of ,aristotle#a and ,theophrastus#b on the production of black1 are derived from the observation of the action of fire1 and on one occasion1 the former distinctly alludes to the terracotta kiln4 ,that the above opinion as to the nature of black was prevalent in the sixteenth century1 may be inferred from ,lomazzo1 who observes1--,quanto all' origine e generazione de' colori1 la frigidit la madre della bianchezza3 il calore padre del nero4#c ,the positive coldness of black may be said to begin when it approaches grey4 ,when ,leonardo da ,vinci says that black is most beautiful in shade1 he probably means to define its most intense and transparent state1 when it is furthest removed from grey4 #a ,de ,coloribus4 #b ,de ,igne4 #c ,trattato1 c4 p4 #aia1 the rest of the passage1 it must be admitted1 abounds with absurdities4 ,,note ,v4--,par4 #eee4 ,the nature of vehicles or liquid mediums to combine with the substance of colours1 has been frequently discussed by modern writers on art1 and may perhaps be said to have received as much attention as it deserves4 ,reynolds smiles at the notion of our not having materials equal to those of former times1 and indeed1 although the methods of individuals will always differ1 there seems no reason to suppose that any great technical secret has been lost4 ,in these inquiries1 however1 which relate merely to the mechanical causes of bright and durable colouring1 the skill of the painter in the adequate employment of the higher resources of his art is1 as if by common consent1 left out of the account1 and without departing from this mode of considering the question1 we would merely repeat a conviction before expressed1 viz4 that the preservation of internal brightness1 a quality compatible with various methods1 has had more to do with the splendour and durability of finely coloured pictures than any vehicle4 ,the observations that follow are therefore merely intended to show how far the older written authorities on this subject agree with the results of modern investigation1 without at all assuming that the old methods1 if known1 need be implicitly followed4 ,on a careful examination of the earlier pictures1 it is said that a resinous substance appears to have been mingled with the colours together with the oil2 that the fracture of the indurated pigment is shining1 and that the surface resists the ordinary solvents4#a ,this admixture of resinous solutions or varnishes with the solid is not alluded to1 as far as we have seen1 by any of the writers on ,italian practice1 but as the method corresponds with that now prevalent in ,england1 the above hypothesis is not likely to be objected to for the present4 ,various local circumstances and relations might seem to warrant the supposition that the ,venetian painters used resinous substances4 ,an important branch of commerce between the mountains of ,friuli and ,venice still consists in the turpentine or fir-resin4#b ,similar substances produced from various trees1 and known under the common name of balsams1#c were imported from the ,east through ,venice1 for general use1 before the ,american balsams#d in some degree superseded them2 and a ,venetian painter1 ,marco ,boschini1 in his description of the ,archipelago1 does not omit to speak of the abundance of mastic produced in the island of ,scio4#e ,the testimonies1 direct or indirect1 against the employment of any such substances by the ,venetian painters1 in the solid part of their work1 seem1 notwithstanding1 very conclusive2 we begin with the writer just named4 ,in his principal composition1 a poem#f describing the practice and the productions of the ,venetian painters1 ,boschini speaks of certain colours which they shunned1 and adds3--,in like manner 7they avoided7 shining liquids and varnishes1 which ,i should rather call lackers2#g for the surface of flesh1 if natural and unadorned1 assuredly does not shine1 nature speaks as to this plainly4 ,after alluding to the possible alteration of this natural appearance by means of cosmetics1 he continues3 ,foreign artists set such great store by these varnishes1 that a shining surface seems to them the only desirable quality in art4 ,what trash it is they prize6 fir-resin1 mastic1 and sandarach1 and larch-resin 7not to say treacle71 stuff fit to polish boots4#h ,if those great painters of ours had to represent armour1 a gold vase1 a mirror1 or anything of the kind1 they made it shine with 7simple7 colours4#i ,this writer so frequently alludes to the ,flemish painters1 of whose great reputation he sometimes seems jealous1 that the above strong expression of opinion may have been pointed at them4 ,on the other hand it is to be observed that the term forestieri1 strangers1 does not necessarily mean transalpine foreigners1 but includes those ,italians who were not of the ,venetian state4#aj ,the directions given by ,raphael ,borghini1#aa and after him by ,armenini1#ab respecting the use and preparation of varnishes made from the very materials in question1 may thus have been comprehended in the censure1 especially as some of these recipes were copied and republished in ,venice by ,bisagno1#ac in #afdb--that is1 only six years before ,boschini's poem appeared4 ,ridolfi's ,lives of the ,venetian ,painters#ad 7#afdh7 may be mentioned with the two last4 ,his only observation respecting the vehicle is1 that ,giovanni ,bellini1 after introducing himself by an artifice into the painting-room of ,antonello da ,messina1 saw that painter dip his brush from time to time in linseed oil4 ,this story1 related about two hundred years after the supposed event1 is certainly not to be adduced as very striking evidence in any way4#ae ,among the next writers1 in order of time prior to ,bisagno1 may be mentioned ,canepario#af 7#afai74 ,his work1 ,de ,atramentis contains a variety of recipes for different purposes3 one chapter1 ,de atramentis diversicoloribus1 has a more direct reference to painting4 ,his observations under this head are by no means confined to the preparation of transparent colours1 but he says little on the subject of varnishes4 ,after describing a mode of preserving white of egg1 he says1 ,others are accustomed to mix colours in liquid varnish and linseed1 or nut-oil2 for a liquid and oily varnish binds the 7different layers of7 colours better together1 and thus forms a very fit glazing material4#ag ,on the subject of oils he observes1 that linseed oil was in great request among painters2 who1 however1 were of opinion that nut-oil-excelled it in giving brilliancy to pictures1 in preserving them better1 and in rendering the colours more vivid4#ah ,lomazzo 7a ,milanese7 says nothing on the subject of vehicles in his principal work1 but in his ,idea del ,tempio della ,pittura1#ai he speaks of grinding the colours in nut-oil1 and spike-oil1 and other things1 the and here evidently means or1 and by other things we are perhaps to understand other oils1 poppy oil1 drying oils1 c4 ,the directions of ,raphael ,borghini and ,vasari#bj cannot certainly be considered conclusive as to the practice of the ,venetians1 but they are very clear on the subject of varnish4 ,these writers may be considered the earliest ,italian authorities who have entered much into practical methods4 ,in the few observations on the subject of vehicles in ,leonardo da ,vinci's treatise1 there is nothing1 as ,m4 ,merime observes1 to show that he was in the habit of mixing varnish with his colours4 ,cennini says but little on the subject of oil-painting2 ,leon ,battista ,alberti is theoretical rather than practical1 and the published extracts of ,lorenzo ,ghiberti's ,,ms4 chiefly relate to sculpture4 ,borghini and ,vasari agree in recommending nut-oil in preference to linseed-oil2 both recommend adding varnish to the colours in painting on walls in oil1 because the work does not then require to be varnished afterwards1 but in the ordinary modes of painting on panel or cloth1 the varnish is omitted4 ,borghini expressly says1 that oil alone 7senza pi7 is to be employed2 he also recommends a very sparing use of it4 ,the treatise of ,armenini 7#aehg7 was published at ,ravenna1 and he himself was of ,faenza1 so that his authority1 again1 cannot be considered decisive as to the ,venetian practice4 ,after all1 he recommends the addition of common varnish only for the ground or preparation1 as a consolidating medium1 for the glazing colours1 and for those dark pigments which are slow in drying4 ,many of his directions are copied from the writers last named2 the recipes for varnishes1 in particular1 are to be found in ,borghini4 ,christoforo ,sorte#ba 7#aehj7 briefly alludes to the subject in question4 ,after speaking of the methods of distemper1 he observes that the same colours may be used in oil1 except that instead of mixing them with size1 they are mixed on the palette with nut-oil1 or 7if slow in drying7 with boiled linseed-oil3 he does not mention varnish4 ,the ,italian writers next in order are earlier than ,vasari1 and may therefore be considered original1 but they are all very concise4 ,the treatise of ,michael ,angelo ,biondo#bb 7#aedi71 remarkable for its historical mistakes1 is not without interest in other respects4 ,the list of colours he gives is1 in all probability1 a catalogue of those in general use in ,venice at the period he wrote4 ,with regard to the vehicle1 he merely mentions oil and size as the mediums for the two distinct methods of oil-painting and distemper1 and does not speak of varnish4 ,the passages in the ,dialogue of ,doni#bc 7#aedi71 which relate to the subject in question1 are to the same effect4 ,in colouring in oil1 he observes1 the most brilliant colours 7that we see in pictures7 are prepared by merely mixing them with the end of a knife on the palette4 ,speaking of the perishable nature of works in oil-painting as compared with sculpture1 he says1 that the plaster of ,paris 7gesso7 and mastic1 with other ingredients of which the ground is prepared1 are liable to decay1 c42 and elsewhere1 in comparing painting in general with mosaic1 that in the former the colours must of necessity be mixed with various things1 such as oils1 gums1 white or yolk of egg1 and juice of figs1 all which tend to impair the beauty of the tints4 ,this catalogue of vehicles is derived from all kinds of painting to enforce the argument1 and is by no means to be understood as belonging to one and the same method4 ,an interesting little work1#bd still in the form of a dialogue 7,fabio and ,lauro71 appeared a year earlier2 the author1 ,paolo ,pino1 was a ,venetian painter4 ,in speaking of the practical methods ,fabio observes1 as usual1 that oil-painting is of all modes of imitation the most perfect1 but his reasons for this opinion seem to have a reference to the ,venetian practice of going over the work repeatedly4 ,lauro asks whether it is not possible to paint in oil on the dry wall1 as ,sebastian del ,piombo did4 ,fabio answers1 the work cannot last1 for the solidity of the plaster is impenetrable1 and the colours1 whether in oil or distemper1 cannot pass the surface4 ,this might seem to warrant the inference that absorbent grounds were prepared for oil-painting1 but there are proofs enough that resins as well as oil were used with the gesso to make the preparation compact4 ,see ,doni1 ,armenini1 c4 ,this writer1 again1 does not speak of varnish4 ,these appear to be the chief ,venetian and ,italian authorities#be of the sixteenth and part of the following century2 and although ,boschini wrote latest1 he appears to have had his information from good sources1 and more than once distinctly quotes ,palma ,giovane4 ,in all these instances it will be seen that there is no allusion to the immixture of varnishes with the solid colours1 except in painting on walls in oil1 and that the processes of distemper and oil are always considered as separate arts4#bf ,on the other hand1 the prohibition of ,boschini cannot be understood to be universal1 for it is quite certain that the ,venetians varnished their pictures when done4#bg ,after ,titian had finished his whole-length portrait of ,pope ,paul ,,iii4 it was placed in the sun to be varnished4#bh ,again1 in the archives of the church of ,s4 ,niccolo at ,treviso a sum is noted 7,sept4 #ba1 #aeba 71 per far la vernise da invernisar la ,pala dell' altar grando1 and the same day a second entry appears of a payment to a painter1 per esser venuto a dar la vernise alla ,pala1 c4#bi ,it is to be observed that in both these cases the pictures were varnished as soon as done2#cj the varnish employed was perhaps the thin compound of naphtha 7oglio di sasso7 and melted turpentine 7oglio d'abezzo71 described by ,borghini1 and after him by ,armenini3 the last-named writer remarks that he had seen this varnish used by the best painters in ,lombardy1 and had heard that it was preferred by ,correggio4 ,the consequence of this immediate varnishing may have been that the warm resinous liquid1 whatever it was1 became united with the colours1 and thus at a future time the pigment may have acquired a consistency capable of resisting the ordinary solvents4 ,not only was the surface of the picture required to be warm1 but the varnish was applied soon after it was taken from the fire4#ca ,many of the treatises above quoted contain directions for making the colours dry3#cb some of these recipes1 and many in addition1 are to be found in ,palomino1 who1 however defective as an historian1#cc has left very copious practical details1 evidently of ancient date4 ,his drying recipes are numerous1 and although sugar of lead does not appear1 cardenillo 7verdigris71 which is perhaps as objectionable1 is admitted to be the best of all dryers4 ,it may excite some surprise that the ,spanish painters should have bestowed so much attention on this subject in a climate like theirs1 but the rapidity of their execution must have often required such an assistance4#cd ,one circumstance alluded to by ,palomino1 in his very minute practical directions1 deserves to be mentioned4 ,after saying what colours should be preserved in their saucers under water1 and what colours should be merely covered with oiled paper because the water injures them1 he proceeds to communicate a curious mode of preserving oil-colours1 and of transporting them from place to place4 ,the important secret is to tie them in bladders1 the mode of doing which he enters into with great minuteness1 as if the invention was recent4 ,it is true1 ,christoforo ,sorte1 in describing his practice in water-colour drawing1 says he was in the habit of preserving a certain vegetable green with gum-water in a bladder2 but as the method was obviously new to ,palomino1 there seems sufficient reason to believe that oil-colours1 when once ground1 had1 up to his time1 been kept in saucers and preserved under water4#ce ,among the items of expense in the ,treviso document before alluded to1 we find a pan and saucers for the painters4#cf ,this is in accordance with ,cennini's directions1 and the same system appears to have been followed till after #agjj4cg ,the ,flemish accounts of the early practice of oil-painting are all later than ,vasari4 ,van ,mander1 in correcting the ,italian historian in his dates1 still follows his narrative in other respects verbatim4 ,if ,vasari's story is to be accepted as true1 it might be inferred that the ,flemish secret consisted in an oil varnish like copal4#ch ,vasari says1 that ,van ,eyck boiled the oils with other ingredients2 that the colours1 when mixed with this kind of oil1 had a very firm consistence2 that the surface of the pictures so executed had a lustre1 so that they needed no varnish when done2 and that the colours were in no danger from water4#ci ,certain colours1 as is well known1 if mixed with oil alone1 may be washed off after a considerable time4 ,leonardo da ,vinci remarks1 that verdigris may be thus removed4 ,carmine1 ,palomino observes1 may be washed off after six years4 ,it is on this account the ,italian writers recommend the use of varnish with certain colours1 and it appears the ,venetians1 and perhaps the ,italians generally1 employed it solely in such cases4 ,but it is somewhat extraordinary that ,vasari should teach a mode of painting in oil so different in its results 7inasmuch as the work thus required varnish at last7 from the ,flemish method which he so much extols--a method which he says the ,italians long endeavoured to find out in vain4 ,if they knew it1 it is evident1 assuming his account to be correct1 that they did not practice it4 #a ,see ,marcucci ,saggio ,analitico-chimico sopra i colori1 c4 ,rome1 #ahaf1 and ,taylor's ,translation of ,merime on ,oil-painting1 ,london1 #ahci4 ,the last-named work contains much useful information4 #b ,italian writers of the #afth century speak of three kinds4 ,cardanus says1 that of the abies was esteemed most1 that of the larix next1 and that of the picea least4 ,the resin extracted by incision from the last 7the pinus abies ,linni7 is known by the name of ,burgundy pitch2 when extracted by fire it is black4 ,the three varieties occur in ,italian treatises on art1 under the names of oglio di abezzo1 trementina and pece ,greca4 #c ,the concrete balsam benzoe1 called by the ,italians beluzino1 and belzoino1 is sometimes spoken of as a varnish4 #d ,marcucci supposes that balsam of copaiba was mixed with the pigments by the 7later7 ,venetians4 #e ,l',archipelago con tutte le ,isole1 ,ven4 #afeh4 ,the incidental notices of the remains of antiquity in this work would be curious and important if they could be relied on4 ,in describing the island of ,samos1 for instance1 the author asserts that the temple of ,juno was in tolerable preservation1 and that the statue was still there4 #f ,la ,carta del ,navegar ,pitoresco1 ,ven4 #affj4 ,it is in the ,venetian dialect4 #g ,inveriadure 7invetriature71 literally the glazing applied to earthenware4 #h ,o de che strazze se fan cavedal6 ,d'ogio d'avezzo1 mastici e sandraca2 ,e trementina 7per no'dir triaca7 ,robe1 che ilustrerave ogni stival4--p4 #cch4 ,the alliteration of the words trementina and triaca is of course lost in a translation4 #i ,i li ha fati straluser co' i colori4 ,boschini was at least constant in his opinion4 ,in the second edition of his ,ricche ,minere della ,pittura ,veneziana1 which appeared fourteen years after the publication of his poem1 he repeats that the ,venetian painters avoided some colours in flesh e similmente i lustri e le vernici4 #aj ,thus1 in the introduction to the ,ricche ,minere1 ,boschini calls the ,milanese1 ,florentine1 ,lombard1 and ,bolognese painters1 forestieri4 #aa ,il ,riposo1 ,firenze1 #aehd4 #ab ,de' ,veri ,precetti della ,pittura1 ,ravenna1 #aehg4 #ac ,trattato della ,pittura fondato nell' autorit di molti eccellenti in questa professione4 ,venezia1 #afdb4 ,bisagno remarks in his preface1 that the books on art were few1 and that painters were in the habit of keeping them secret4 ,he acknowledges that he has availed himself of the labours of others1 but without mentioning his sources3 some passages are copied from ,lomazzo4 ,he1 however1 lays claim to some original observations1 and says he had seen much and discoursed with many excellent painters4 #ad ,le ,meraviglie dell' ,arte1 ,venezia1 #afdh4 #ae ,it has been conjectured by some that this story proved the immixture of varnishes with the colours1 and that the oil was only used to dilute them4 ,the epitaph on ,antonello da ,messina which existed in ,vasari's time1 alludes to his having mixed the colours with oil4 #af ,petri ,mari ,caneparii ,de ,atramentis cujuscumque generis1 ,venet4 #afai4 ,it was republished at ,rotterdam in #agah4 #ag ,ita quod magis ex hiis evadit atramentum pictur summopere idoneum4 ,thus1 if atramentum is to be understood1 as usual1 to mean a glazing colour1 the passage can only refer to the immixture of varnish with the transparent colours applied last in order4 #ah ,in a passage that follows respecting the mode of extracting nut-oil1 ,caneparius appears to mistranslate ,galen1 c4 #g--;,de ,simplicium ,medicamentorum facultatibus4 ,the observations of ,galen on this subject1 and on the drying property of linseed1 may have given the first hint to the inventors of oil-painting4 ,the custom of dating the origin of this art from ,van ,eyck is like that of dating the commencement of modern painting from ,cimabue4 ,the improver is often assumed to be the inventor4 #ai ,milan1 #aeij4 #bj ,the particulars here alluded to are to be found in the first edition of ,vasari 7#aeej7 as well as the second4--v4 i4 c4 #ba1 c4 #ba ,osservasioni nella ,pittura4 ,in ,venezia1 #aehj4 ,sorte1 who1 it appears1 was a native of ,verona1 had worked in his youth with ,giulio ,romano1 at ,mantua1 and communicates the methods taught him by that painter1 for giving the true effects of perspective in compositions of figures4 ,he is1 perhaps1 the earliest who describes the process of water-colour painting as distinguished from distemper and as adapted to landscape1 if the art he describes deserves the name4 #bb ,della nobilissima ,pittura e sua ,arte1 ,venezia1 #aedi4 ,biondo is so ignorant as to attribute the ,last ,supper1 by ,leonardo da ,vinci1 to ,mantegna4 #bc ,disegno del ,doni1 in ,venezia1 #aedi4 #bd ,dialogo di ,pittura1 ,venezia1 #aedh4 ,pino1 in enumerating the celebrated contemporary artists1 does not include ,paul ,veronese1 for a very obvious reason1 that painter being at the time only about #ag years of age4 ,sorte1 who wrote thirty years later1 mentions l'eccellente ,messer ,paulino nostro1 alone4 #be ,the ,dialogues of ,lodovico ,dolce1 and various other works1 are not referred to here1 as they contain nothing on the subject in question4 ,the latest authority at all connected with the traditions of ,venetian practice1 is a certain ,giambatista ,volpato1 of ,bassano3 he died in #agjf1 and had been intimate with ,ridolfi4 ,the only circumstance he has transmitted relating to practical details is that ,giacomo ,bassan1 in retouching on a dry surface1 sometimes adopted a method commonly practised1 he says1 by ,paul ,veronese 7and commonly practised still71 namely1 that of dipping his brush in spirits of turpentine2 at other times he oiled out the surface in the usual manner4 ,volpato left a ,,ms4 which was announced for publication in ,vicenza in #afhe1 but it never appeared2 it1 however1 afterwards formed the ground-work of ,verci's ,notizie intorno alla ,vita e alle ,opere de' ,pittori di ,bassano4 ,venezia1 #agge4 ,see also ,lettera di ,giambatista ,roberti sopra ,giacomo da ,ponte1 ,lugano1 #aggg4 ,another ,,ms4 by ,natale ,melchiori1 of about the same date1 is preserved at ,treviso and ,castel ,franco3 it abounds with historical mistakes2 the author says1 for instance1 that the ,pietro ,martyre was begun by ,giorgione and finished by ,titian4 ,the recipes for varnishes and colours are very numerous1 but they are mostly copied from earlier works4 #bf ,that distemper was not very highly esteemed by the ,venetians may be inferred from the following observation of ,pino3--,il modo di colorir guazzo imperfetto et pi fragile et me non diletta onde lasciamolo all' oltremontani i quali sono privi della vera via4 ,it is1 however1 certain that the ,venetians sometimes painted in this style1 and ,volpato mentions several works of the kind by ,bassan1 but he never hints that he began his oil pictures in distemper4 #bg ,boschini says1 that the ,venetians 7he especially means ,titian7 rendered their pictures sparkling by finally touching on a dry surface 7 secco74 ,the absence of varnish in the solid colours1 the retouching with spirit of turpentine1 and even secco1 all suppose a dull surface1 which would require varnish4 ,the latter method1 alluded to by ,boschini1 was an exception to the general practice1 and not likely to be followed on account of its difficulty4 ,carlo ,maratti1 on the authority of ,palomino1 used to say1 ,he must be a skilful painter who can retouch without oiling out4 #bh ,see a letter by ,francesco ,bocchi1 and another by ,vasari1 in the ,lettere ,pittoriche of ,bottari4 ,the circumstance is mentioned incidentally2 the point chiefly dwelt on is1 that some persons who passed were deceived1 and bowed to the picture1 supposing it to be the pope4 #bi ,federici1 ,memorie ,trevigiane1 ,venezia1 #ahjc4 ,the altar-piece of ,s4 ,niccolo at ,treviso is attributed1 in the document alluded to1 to ,fra ,marco ,pensabene1 a name unknown2 the painting is so excellent as to have been thought worthy of ,sebastian del ,piombo3 for this opinion1 however1 there are no historical grounds4 ,it was begun in #aebj1 but before it was quite finished the painter1 whoever he was1 absconded3 it was therefore completed by another4 #cj ,titian's stay in ,rome was short1 and with respect to the ,treviso altar-piece1 a week or two only1 at most1 can have elapsed between the completion and the varnishing4 ,cennini1 who recommends delaying a year at least before varnishing1 speaks of pictures in distemper4 #ca ,see ,borghini1 ,armenini1 their ,venetian copyist ,bisagno1 and ,palomino4 ,the last-named writer1 though of another school and much more modern1 was evidently well acquainted with the ancient methods3 he says1 ,se advierte que siempre que se huviere de barnizar alguna cosa conviene que la pintura y el barniz estn calientes4--,el ,museo ,pictorico1 v4 ii4 #cb ,burnt alum1 one of the ingredients recommended1 might perhaps account for a shining fracture in the indurated pigment in some old pictures4 #cc ,of the earlier ,spanish writers ,pacheco may be mentioned next to ,palomino as containing most practical information4 ,carducho1 ,de ,butron1 and others1 seldom descend to such details4 ,palomino contains all the directions of ,pacheco1 and many in addition4 #cd ,see ,cean ,bermudez1 ,sobre la ,escuela ,sevillana1 ,cadiz1 #ahjf4 ,the same reasons induced the later ,venetian machinists to paint on dark grounds1 and to make use of 7drying7 oil in excess4 ,see ,zanetti1 ,della ,pittura ,veneziana1 #a4 iv4 #ce ,borghini1 in describing the method of making a gold-size 7the same as ,cennini's71 speaks of boiling the buccie de' colori in oil2 this only means the skin or pellicle of the colour itself--in fact1 he proceeds to say that they dissolve in boiling4 ,vasari1 in describing the same process1 uses the expression colori seccaticci4 #cf ,maggio #d 7#aebj7 ,per un cadin 7catino7 per depentori4 ,per scudellini per li depentori4--,mem4 ,trev41 vol4 i4 p4 #aca4 ,pungileoni 7,memorie ,istoriche di ,antonio ,allegri7 quotes a note of expenses relating to two oil-pictures by ,paolo ,gianotti2 among the items we find colori1 telari1 et brocchette4--vol4 ii4 p4 #ge4 #cg ,salmon1 in his ,polygraphice 7#agja71 gives the following direction3--,oyl colors1 if not presently used1 will have a skin grow over them1 to prevent which put them into a glass1 and put the glass three or four inches under water1 c4 #ch ,this varnish appears to have been known some centuries before ,van ,eyck's time1 but he may have been the first to mix it with the colours4 #ci ,see ,vasari1 ,life of ,antonello da ,messina4 ,,note ,w4--,par4 #fjh4 ,in the second volume ,goethe gives the nomenclature of the ,greeks and ,romans at some length4 ,the general notions of the ancients with regard to colours are thus described3--,the ancients derive all colours from white and black1 from light and darkness4 ,they say1 all colours are between white and black1 and are mixed out of these4 ,we must not1 however1 suppose that they understand by this a mere atomic mixture1 although they occasionally use the word 2#a for in the remarkable passages1 where they wish to express a kind of reciprocal 7dynamic7 action of the two contrasting principles1 they employ the words 1 union1 1 combination2 thus1 again1 the mutual influence of light and darkness1 and of colours among each other1 is described by the word 1 an expression of similar import4 ,the varieties of colours are differently enumerated2 some mention seven1 others twelve1 but without giving the complete list4 ,from a consideration of the terminology both of the ,greeks and ,romans1 it appears that they sometimes employed general for specific terms1 and vice vers4 ,their denominations of colours are not permanently and precisely defined1 but mutable and fluctuating1 for they are employed even with regard to similar colours both on the plus and minus side4 ,their yellow1 on the one hand1 inclines to red1 on the other to blue2 the blue is sometimes green1 sometimes red2 the red is at one time yellow1 at another blue4 ,pure red 7purpur7 fluctuates between warm red and blue1 sometimes inclining to scarlet1 sometimes to violet4 ,thus the ancients not only seem to have looked upon colour as a mutable and fleeting quality1 but appear to have had a presentiment of the 7physical and chemical7 effects of augmentation and re-action4 ,in speaking of colours they make use of expressions which indicate this knowledge2 they make yellow redden1 because its augmentation tends to red2 they make red become yellow1 for it often returns thus to its origin4 ,the hues thus specified undergo new modifications4 ,the colours arrested at a given point are attenuated by a stronger light darkened by a shadow1 nay1 deepened and condensed in themselves4 ,for the gradations which thus arise the name of the species only is often given1 but the more generic terms are also employed4 ,every colour1 of whatever kind1 can1 according to the same view1 be multiplied into itself1 condensed1 enriched1 and will in consequence appear more or less dark4 ,the ancients called colour in this state1 c4 ,then follow the designations of general states of colour and those of specific hues4 ,another essay on the notions of the ancients respecting the origin and nature of colour generally1 shows how nearly ,goethe himself has followed in the same track4 ,the dilating effect of light objects1 the action and reaction of the retina1 the coloured after-image1 the general law of contrast1 the effect of semi-transparent mediums in producing warm or cold colours as they are interposed before a dark or light background--all this is either distinctly expressed or hinted at2 but1 continues ,goethe1 how a single element divides itself into two1 remained a secret for them4 ,they knew the nature of the magnet1 in amber1 only as attraction2 polarity was not yet distinctly evident to them4 ,and in very modern times have we not found that scientific men have still given their almost exclusive attention to attraction1 and considered the immediately excited repulsion only as a mere after-action8 ,an essay on the ,painting of the ,ancients#b was contributed by ,heinrich ,meyer4 #a ,see ,note on ,par4 #agg4 #b ,vol4 ii4 p4 #fi1 first edition4 ,,note ,x4--,par4 #fgj4 ,this agrees with the general recommendation so often given by high authorities in art1 to avoid a tinted look in the colour of flesh4 ,the great example of ,rubens1 whose practice was sometimes an exception to this1 may however show that no rule of art is to be blindly or exclusively adhered to4 ,reynolds1 nevertheless1 in the midst of his admiration for this great painter1 considered the example dangerous1 and more than once expresses himself to this effect1 observing on one occasion that ,rubens1 like ,baroccio1 is sometimes open to the criticism made on an ancient painter1 namely1 that his figures looked as if they fed on roses4 ,lodovico ,dolce1 who is supposed to have given the viv voce precepts of ,titian in his ,dialogue1#a makes ,aretino say3 ,i would generally banish from my pictures those vermilion cheeks with coral lips2 for faces thus treated look like masks4 ,propertius1 reproving his ,cynthia for using cosmetics1 desires that her complexion might exhibit the simplicity and purity of colour which is seen in the works of ,apelles4 ,those who have written on the practice of painting have always recommended the use of few colours for flesh4 ,reynolds and others quote even ancient authorities as recorded by ,pliny1 and ,boschini gives several descriptions of the method of the ,venetians1 and particularly of ,titian1 to the same effect4 ,they used1 he says1 earths more than any other colour1 and at the utmost only added a little vermilion1 minium1 and lake1 abhorring as a pestilence biadetti1 gialli santi1 smaltini1 verdi-azzurri1 giallolini4#b ,elsewhere he says1#c ,earths should be used rather than other colours3 after repeating the above prohibited list he adds1 ,i speak of the imitation of flesh1 for in other things every colour is good2 again1 ,our great ,titian used to say that he who wishes to be a painter should be acquainted with three colours1 white1 black1 and red4#d ,assuming this account to be a little exaggerated1 it is still to be observed that the monotony to which the use of few colours would seem to tend1 is prevented by the nature of the ,venetian process1 which was sufficiently conformable to ,goethe's doctrine2 the gradations being multiplied1 and the effect of the colours heightened by using them as semi-opaque mediums4 ,immediately after the passage last quoted we read1 ,he also gave this true precept1 that to produce a lively colouring in flesh it is not possible to finish at once4#e ,as these particulars may not be known to all1 we add some further abridged extracts explaining the order and methods of these different operations4 ,the ,venetian painters1 says this writer1#f after having drawn in their subject1 got in the masses with very solid colour1 without making use of nature or statues4 ,their great object in this stage of their work was to distinguish the advancing and retiring portions1 that the figures might be relieved by means of chiaro-scuro--one of the most important departments of colour and form1 and indeed of invention4 ,having decided on their scheme of effect1 when this preparation was dry1 they consulted nature and the antique2 not servilely1 but with the aid of a few lines on paper 7quattro segni in carta7 they corrected their figures without any other model4 ,then returning to their brushes1 they began to paint smartly on this preparation1 producing the colour of flesh4 ,the passage before quoted follows1 stating that they used earths chiefly1 that they carefully avoided certain colours1 and likewise varnishes and whatever produces a shining surface4#g ,when this second painting was dry1 they proceeded to scumble over this or that figure with a low tint to make the one next it come forward1 giving another1 at the same time1 an additional light--for example1 on a head1 a hand1 or a foot1 thus detaching them1 so to speak1 from the canvas4 7,tintoret's ,prigionia di ,s4 ,rocco is here quoted47 ,by thus still multiplying these well-understood retouchings where required1 on the dry surface1 7 secco7 they reduced the whole to harmony4 ,in this operation they took care not to cover entire figures1 but rather went on gemming them 7gioielandole7 with vigorous touches4 ,in the shadows1 too1 they infused vigour frequently by glazing with asphaltum1 always leaving great masses in middle-tint1 with many darks1 in addition to the partial glazings1 and few lights4 ,the introduction to the subject of ,venetian colouring1 in the poem by the same author1 is also worth transcribing1 but as the style is quaint and very concise1 a translation is necessarily a paraphrase4#h ,the art of colouring has the imitation of qualities for its object2 not all qualities1 but those secondary ones which are appreciable by the sense of sight4 ,the eye especially sees colours1 the imitation of nature in painting is therefore justly called colouring2 but the painter arrives at his end by indirect means4 ,he gives the varieties of tone in masses2#i he smartly impinges lights1 he clothes his preparation with more delicate local hues1 he unites1 he glazes3 thus everything depends on the method1 on the process4 ,for if we look at colour abstractedly1 the most positive may be called the most beautiful1 but if we keep the end of imitation in view1 this shallow conclusion falls to the ground4 ,the refined ,venetian manner is very different from mere direct1 sedulous imitation4 ,every one who has a good eye may arrive at such results1 but to attain the manner of ,paolo1 of ,bassan1 of ,palma1 ,tintoret1 or ,titian1 is a very different undertaking4#aj ,the effects of semi-transparent mediums in some natural productions seem alluded to in the following passage--,nature sometimes accidentally imitates figures in stones and other substances1 and although they are necessarily incomplete in form1 yet the principle of effect 7depth7 resembles the ,venetian practice4 ,in a passage that follows there appears to be an allusion to the production of the atmospheric colours by semi-transparent mediums4#aa #a ,dialogo della ,pittura1 intitolato l',aretino4 ,it was first published at ,venice in #aeeg2 about twenty years before ,titian's death4 ,in the dedication to the senator ,loredano1 ,lodovico ,dolce eulogises the work1 which he would hardly have done if it had been entirely his own3 again1 the supposition that it may have been suggested by ,aretino1 would be equally conclusive1 coupled with internal evidence1 as to the original source4 #b ,introduction to the ,ricche ,minere della ,pittura ,veneziana1 ,venezia1 #afgd4 ,the ,italian annotators on older works on painting are sometimes at a loss to find modern terms equivalent to the obsolete names of pigments4 7,see ,antologia dell ',arte ,pittorica47 ,the colours now in use corresponding with ,boschini's list1 are probably yellow lakes1 smalt1 verditer1 and ,naples yellow4 ,boschini often censures the practice of other schools1 and in this emphatic condemnation he seems to have had an eye to certain precepts in ,lomazzo1 and perhaps1 even in ,leonardo da ,vinci1 who1 on one occasion1 recommends ,naples yellow1 lake1 and white for flesh4 ,the ,venetian writer often speaks1 too1 in no measured terms of certain ,flemish pictures1 probably because they appeared to him too tinted4 #c ,la ,carta del ,navegar ,pitoresco1 p4 #cch4 #d ,ib4 p4 #cda4 ,in describing ,titian's actual practice 7,ricche ,minere71 he1 however1 adds yellow 7ochre74 ,the red is also particularised1 viz41 the common terra rossa4 #e ,high examples here again prove that the opposite system may attain results quite as successful4 #f ,introduction to the ,ricche ,minere4 #g ,see ,note to ,par4 #eee4 ,here again1 assuming the description to be correct1 high authorities might be opposed to the ,venetians4 #h ,the following quatrain may serve as a specimen2 the author is speaking of the importance of the colour of flesh as conducive to picturesque effect3-- ,importa el nudo2 e come ben l'importa6 ,un quadro senta nudo come aponto ,un disnar senza pan1 se ben ghe zonto1 ,per pi delicia1 confetura e torta4--p4 #cdf4 ,in his preface he anticipates1 and thus answers the objections to his ,venetian dialect--,mi1 che son ,venetian in ,venetia e che parlo de' ,pitori ,venetiani h da andarme a stravestir8 ,guarda el ,cielo4 #i ,the word ,macchia1 literally a blot1 is generally used by ,italian writers1 by ,vasari for instance1 for the local colour4 ,boschini understands by it the relative depth of tones rather than the mere difference of hue4 ,by macchia1 he says1 ,i understand that treatment by which the figures are distinguished from each other by different tones lighter or darker4--,la ,carta del ,navegar1 p4 #cbh4 ,elsewhere1 ,colouring 7as practised by the ,venetians7 comprehends both the macchia and drawing2 7p4 #cjj7 that is1 comprehends the gradations of light and dark in objects1 and the parts of objects1 and consequently1 their essential form4 ,the macchia1 he adds1 is the effect of practice1 and is dictated by the knowledge of what is requisite for effect4 #aj ,ma l'arivar a la maniera1 al trato 7,verbi gratia7 de ,paulo1 del ,bassan1 ,del ,vechio1 ,tentoreto1 e di ,tician1 ,per ,dio1 l' cosa da deventar mato4--p4 #bid1 #big4 #aa ,the traces of the ,aristotelian theory are quite as apparent in ,boschini as in the other ,italian writers on art2 but as he wrote in the seventeenth century1 his authority in this respect is only important as an indication of the earlier prevalence of the doctrine4 ,,note ,y4--,par4 #fgb4 ,the author's conclusion here is unsatisfactory1 for the colour of the black races may be considered at least quite as negative as that of ,europeans4 ,it would be safer to say that the white skin is more beautiful than the black1 because it is more capable of indications of life1 and indications of emotion4 ,a degree of light which would fail to exhibit the finer varieties of form on a dark surface1 would be sufficient to display them on a light one2 and the delicate mantlings of colour1 whether the result of action or emotion1 are more perceptible for the same reason4 ,,note ,z4--,par4 #fij4 ,the author appears to mean that a degree of brightness which the organ can bear at all1 must of necessity be removed from dazzling1 white light4 ,the slightest tinge of colour to this brightness1 implies that it is seen through a medium1 and thus1 in painting1 the lightest1 whitest surface should partake of the quality of depth4 ,goethe's view here again accords1 it must be admitted1 with the practice of the best colourists1 and with the precepts of the highest authorities4--,see ,note ,c4 ,,note ,a ,a4--,par4 #gcb4 ,ample details respecting the opinions of ,louis ,bertrand ,castel1 a ,jesuit1 are given in the historical part4 ,the coincidence of some of his views with those of ,goethe is often apparent3 he objects1 for instance1 to the arbitrary selection of the ,newtonian spectrum2 observing that the colours change with every change of distance between the prism and the recipient surface4--,farbenl4 vol4 ii4 p4 #ebg4 ,jeremias ,friedrich ,glich was a dyer in the neighbourhood of ,stutgardt3 he published an elaborate work on the technical details of his own pursuit4--,farbenl4 vol4 ii4 p4 #fcj4 ,,note ,b ,b4--,par4 #gdh4 ,goethe1 in his account of ,castel1 suppresses the learned ,jesuit's attempt at colorific music 7the clavein oculaire71 founded on the ,newtonian doctrine4 ,castel was complimented1 perhaps ironically1 on having been the first to remark that there were but three principal colours4 ,in asserting his claim to the discovery1 he admits that there is nothing new4 ,in fact1 the notion of three colours is to be found in ,aristotle2 for that philosopher enumerates no more in speaking of the rainbow1#a and ,seneca calls them by their right names4#b ,compare with ,dante1 ,parad4 c4 #cc4 ,the relation between colours and sounds is in like manner adverted to by ,aristotle2 he says--,it is possible that colours may stand in relation to each other in the same manner as concords in music1 for the colours which are 7to each other7 in proportions corresponding with the musical concords1 are those which appear to be the most agreeable4#c ,in the latter part of the #afth century1 ,arcimboldo1 a ,milanese painter1 invented a colorific music2 an account of his principles and method will be found in a treatise on painting which appeared about the same time4 ,ammaestrato dal quai ordine ,mauro ,cremonese dalla viola1 musico dell' ,imperadore ,ridolfo ,,ii4 trov sul gravicembalo tutte quelle consonanze che dall' ,arcimboldo erano segnate coi colori sopra una carta4#d #a ,de ,meteor41 lib4 #c1 c4 ii4 and iv4 ,he observes that this is the only effect of colour which painters cannot imitate4 #b ,de ,ignib4 clest4 ,the description of the prism by ,seneca is another instance of the truth of ,castel's admission4 ,the ,roman philosopher's words are--,virgula solet fieri vitrea1 stricta vel pluribus angulis in modo clav tortuos2 hc si ex transverso solem accipit colorem talem qualis in arcu videri solet1 reddit1 c4 #c ,de ,sensu et sensili4 #d ,il ,figino1 overo del ,fine della ,pittura1 ,mantova1 #aeia1 p4 #bdi4 ,an account of the absurd invention of the same painter in composing figures of flowers and animals1 and even painting portraits in this way1 to the great delight of the emperor1 will be found in the same work4 ,,note ,c ,c4--,par4 #geh4 ,the moral associations of colours have always been a more favourite subject with poets than with painters4 ,this is to be traced to the materials and means of description as distinguished from those of representation4 ,an image is more distinct for the mind when it is compared with something that resembles it4 ,an object is more distinct for the eye when it is compared with something that differs from it4 ,association is the auxiliary in the one case1 contrast in the other4 ,the poet1 of necessity1 succeeds best in conveying the impression of external things by the aid of analogous rather than of opposite qualities3 so far from losing their effect by this means1 the images gain in distinctness4 ,comparisons that are utterly false and groundless never strike us as such if the great end is accomplished of placing the thing described more vividly before the imagination4 ,in the common language of laudatory description the colour of flesh is like snow mixed with vermilion3 these are the words used by ,aretino in one of his letters in speaking of a figure of ,st4 ,john1 by ,titian4 ,similar instances without end might be quoted from poets3 even a contrast can only be strongly conveyed in description by another contrast that resembles it4#a ,on the other hand it would be easy to show that whenever poets have attempted the painter's method of direct contrast1 the image has failed to be striking1 for the mind's eye cannot see the relation between two colours4 ,under the same category of effect produced by association may be classed the moral qualities in which poets have judiciously taken refuge when describing visible forms and colours1 to avoid competition with the painters' elements1 or rather to attain their end more completely4 ,but a little examination would show that very pleasing moral associations may be connected with colours which would be far from agreeable to the eye4 ,all light1 positive colours1 light-green1 light-purple1 white1 are pleasing to the mind's eye1 and no degree of dazzling splendour is offensive4 ,the moment1 however1 we have to do with the actual sense of vision1 the susceptibility of the eye itself is to be considered1 the law of comparison is reversed1 colours become striking by being opposed to what they are not1 and their moral associations are not owing to the colours themselves1 but to the modifications such colours undergo in consequence of what surrounds them4 ,this view1 so naturally consequent on the principles the author has himself arrived at1 appears to be overlooked in the chapter under consideration1 the remarks in which1 in other respects1 are acute and ingenious4 #a ,such as-- ,her beauty hangs upon the cheek of night1 ,like a rich jewel in an ,ethiop's ear4 ,romeo and ,juliet4 ,,note ,d ,d4--,par4 #hdi4 ,according to the usual acceptation of the term chiaro-scuro in the artist world1 it means not only the mutable effects produced by light and shade1 but also the permanent differences in brightness and darkness which are owing to the varieties of local colour4 ,,note ,e ,e4--,par4 #hee4 ,the mannered treatment of light and shade here alluded to by the author is very seldom to be met with in the works of the colourists2 the taste may have first arisen from the use of plaster-casts1 and was most prevalent in ,france and ,italy in the early part of the last century4 ,piazzetta represented it in ,venice1 ,subleyras in ,rome4 ,in ,france ,restout taught his pupils that a globe ought to be represented as a polyhedron4 ,greuze most implicitly adopted the doctrine1 and in practice showed that he considered the round cheeks of a young girl or an infant as bodies cut into facettes4#a #a ,see ,taylor's translation of ,merime on oil-painting1 p4 #bg4 ,barry1 in a letter from ,paris1 speaks of ,restout as the only painter who resembled the earlier ,french masters3 the manner in question is undoubtedly sometimes very observable in ,poussin4 ,the ,english artist elsewhere speaks of the broad1 happy manner of ,subleyras4--,works1 ,london1 #ahji4 ,,note ,f ,f4--,par4 #hei4 ,all this was no doubt suggested by ,heinrich ,meyer1 whose chief occupation in ,rome1 at one time1 was making sepia drawings from sculpture 7see ,goethe's ,italinische ,reise74 ,it is hardly necessary to say that the observation respecting the treatment of the surface in the antique statues is very fanciful4 ,,note ,g ,g4--,par4 #hfc4 ,this observation might have been suggested by the drawings of ,claude1 which1 with the slightest means1 exhibit an harmonious balance of warm and cold4 ,,note ,h ,h4--,par4 #hfe4 ,the colouring of ,paolo ,uccello1 according to ,vasari's account of him1 was occasionally so remarkable that he might perhaps have been fairly included among the instances of defective vision given by the author4 ,his skill in perspective1 indicating an eye for gradation1 may be also reckoned among the points of resemblance 7see ,par4 #aje74 ,,note ,i ,i4--,par4 #ijb4 ,the quotation before given from ,boschini shows that the method described by the author1 and which is true with regard to some of the ,florentine painters1 was not practised by the ,venetians1 for their first painting was very solid4 ,it agrees1 however1 with the manner of ,rubens1 many of whose works sufficiently corroborate the account of his process given by ,descamps4 ,in the early state of ,rubens's pictures1 says that writer1#a everything appeared like a thin wash2 but although he often made use of the ground in producing his tones1 the canvas was entirely covered more or less with colour4 ,in this system of leaving the shadows transparent from the first1 with the ground shining through them1 it would have been obviously destructive of richness to use white mixed with the darks1 the brightness1 in fact1 already existed underneath4 ,hence the well-known precept of ,rubens to avoid white in the shadows1 a precept1 like many others1 belonging to a particular practice1 and involving all the conditions of that practice4#b ,scarmiglione1 whose ,aristotelian treatise on colour was published in ,germany when ,rubens was three-and-twenty1 observes1 ,painters1 with consummate art1 lock up the bright colours with dark ones1 and1 on the other hand1 employ white1 the poison of a picture1 very sparingly4 7,artificiosissim pictores claros obscuris obsepiant et contra candido picturarum veneno summ parcentes1 c47 #a ,la ,vie des ,peintres ,flamands1 vol4 i4 #b ,the method he recommended for keeping the colours pure in the lights1 viz4 to place the tints next each other unmixed1 and then slightly to unite them1 may have degenerated to a methodical manner in the hands of his followers4 ,boschini1 who speaks of ,rubens himself with due reverence1 and is far from confounding him with his imitators1 contrasts such a system with that of the ,venetians1 and adds that ,titian used to say1 ,chi de imbratar colori teme1 imbrata e machia si medemi4--,carta del ,navegar1 p4 #cda4 ,the poem of ,boschini is in many respects polemical4 ,he wrote at a time when the ,flemish painters1 having adopted and modified the ,venetian principles1 threatened to supersede the ,italian masters in the opinion of the world4 ,their excellence1 too1 had all the charm of novelty1 for in the seventeenth century ,venice produced no remarkable talent1 and it was precisely the age for her to boast of past glories4 ,the contemptuous manner in which ,boschini speaks of the ,flemish varnishes1 of the fear of mixing tints1 c41 is thus always to be considered with reference to the time and circumstances4 ,so also his boasting that the ,venetian masters painted without nature1 which may be an exaggeration1 is pointed at the ,naturalisti1 ,caravaggio and his followers1 who copied nature literally4 ,,note ,k ,k4--,par4 #ijc4 ,the practice here alluded to is more frequently observable in slight works by ,paul ,veronese4 ,his ground was often pure white1 and in some of his works it is left as such4 ,titian's white ground was covered with a light warm colour1 probably at first1 and appears to have been similar to that to which ,armenini gives the preference1 namely1 quella che tira al color di carne chiarissima con un non so che di fiammeggiante4#a #a ,veri ,precetti della ,pittura1 p4 #abc4 ,,note ,l ,l4--,par4 #iai4 ,the notion which the author has here ventured to express may have been suggested by the remarkable passage in the last canto of ,dante's ,paradiso-- ,nella profonda e chiara sussistenza1 ,dell' alto lume parremi tre giri ,di tre colori e d'una continenza1 c4 ,after the concluding paragraph the author inserts a letter from a landscape-painter1 ,philipp ,otto ,runge1 which is intended to show that those who imitate nature may arrive at principles analogous to those of the ,farbenlehre4 ,,the ,,end4