,,light ,,and ,,colour ,,theories ,illustration3 ,,tintometer4 ,form of ,instrument for ,opaque ,observation4 ,illustration3 ,reproductions of some ,medals awarded to ,,joseph ,w4 ,,lovibond',s ,method of ,colour ,analysis ,,for ,scientific and ,commercial ,purposes4 ,,light ,,and ,,colour ,,theories and their ,relation to ,light and ,colour ,standardization ,by ,,joseph ,w4 ,,lovibond ,,illustrated ,,by #aa ,,plates ,,coloured ,,by ,,hand ,illustration3 ,logo ,london ,e4 ,f4 ,n4 ,,spon1 ,limited1 #eg ,,haymarket ,new ,york ,,spon ,,chamberlain1 #abc ,,liberty ,,street #aiae ,,contents ,,page ,list of ,plates vii ,purpose ix ,,chapter ,i4 ,introduction #a ,,chapter ,,ii4 ,evolution of the ,method #e ,,chapter ,,iii4 ,evolution of the ,unit #i ,,chapter ,,iv4 ,derivation of ,colour from ,white ,light #aa ,,chapter ,v4 ,standard ,white ,light #ad ,,chapter ,,vi4 ,qualitative ,colour ,nomenclature #ag ,,chapter ,,vii4 ,quantitative ,colour ,nomenclature ,,chapter ,,viii4 ,the ,colour ,scales #bh ,,chapter ,,ix4 ,colour ,charts #ca ,,chapter ,x4 ,representations of ,colour in ,space of ,three ,dimensions #cd ,,chapter ,,xi4 ,the ,spectrum in relation to ,colour ,standardization #cf ,,chapter ,,xii4 ,the ,physiological ,light ,unit #de ,,appendix ,i4 ,colour ,education #ei ,,appendix ,,ii4 ,the ,possibilities of a ,standard ,light and ,colour ,unit #fi ,,appendix ,,iii4 ,dr4 ,dudley ,corbett's ,radiometer #hc ,index #hi ,,errata4 ,plate ,i4 ,newton's ,theory4 ,the ,indigo line is erroneously placed between the ,violet and the ,red2 it should be between the ,blue and the ,violet4 ,page #dj4--;,fifth line from the bottom1 for ,fraunhoper read ,fraunhofer4 ,to face p4 vi41 ,lovibond1 ,light and ,colour ,theories4 ,p4,r4 #acag ,,list ,,of ,,plates ,,to ,,face ,,page ,plate ,i4 ,six ,colour ,theories #d ,,ii4 ,circles ,illustrating ,absorption of ,white ,light #aa ,,iii4 ,diagram ,illustrating ,analysis of ,white ,light #ac ,,iv4 ,first ,system of ,charting ,colour #ca ,v4 ,second ,system of ,charting ,colour #cc ,,vi4 ,six ,tintometrical ,colour ,charts #ci ,,vii4 ,two ,circles #dj ,,viii4 ,absorption ,curves of ,dyes #gf ,,ix4 ,fading ,curves of ,dyes #gh ,x4 ,comparison ,curves of ,healthy and ,diseased ,blood #hj ,,xi4 ,specific ,colour ,curves of ,healthy and ,diseased ,human ,blood #hb ,,purpose ,the purpose of this work is to demonstrate that colour is a determinable property of matter1 and to make generally known methods of colour analysis and synthesis which have proved of great practical value in establishing standards of purity in some industries4 ,the purpose is also to show that the methods are thoroughly scientific in theory and practice1 and that the results are not likely to be changed by further discoveries4 ,also that out of the work done a new law has been developed1 which the writer calls the ,law of ,specific ,colour ,development1 meaning that every substance has its own rate of colour development for regularly increasing thicknesses4 ,,the ,,theory4 ,of the six colours in white light--red1 orange1 yellow1 green1 blue and violet2 ,red1 ,yellow and ,blue are regarded as dominants1 because they visually hold the associated colours orange1 green and violet in subjection4 ,an equivalent unit of pure red1 pure yellow and pure blue is adopted1 and incorporated into glass4 ,the unit is multiplied to obtain greater intensities1 and divided to obtain lesser intensities4 ,the coloured glasses are called absorbents4 ,the red absorbent transmits violet1 red and orange1 but the red ray alone is visible as colour1 until the other absorbents are superimposed1 and the character of the group of rays changed4 ,in the same way yellow transmits orange and green1 and blue transmits green and violet1 whilst the yellow and blue alone are visible as colour4 ,orange1 green and violet are here called subordinates1 which may be developed as follows3-- ,or4 ,r4 ,y4 ,gr4 ,y4 ,b4 ,vi4 ,b4 ,r4 ,twenty-five years' experience in the application of the theory and the method to the requirements of practical work1 have given no reason for change4 ,following will be found a list of awards from ,international ,juries and ,scientific ,societies1 also a list of industries in which the writer's method is giving entire satisfaction4 ,awards by ,international ,juries4 ,st4 ,louis #a ,silver ,medal4 #b ,bronze ,medals4 ,brussels #a ,gold ,medal4 #c ,silver ,medals4 ,turin ,diploma of ,honour4 #a ,gold ,medal4 #a ,silver ,medal4 ,awards by ,scientific ,societies4 ,sanitary ,institute of ,great ,britain-- ,bronze ,medal for ,colourometrical ,water ,analysis4 ,royal ,sanitary ,institute-- ,bronze ,medal for ,measuring ,smoke ,densities4 ,international ,congress on ,school ,hygiene-- ,bronze ,medal for ,colour ,educator4 ,royal ,sanitary ,institute-- ,silver ,medal for ,colour ,educator4 ,smoke ,abatement ,society1 ,sheffield-- ,diploma for ,system of ,colour ,measurement4 ,royal ,sanitary ,institute-- ,bronze ,medal for ,quantitative ,estimation of ,colour ,blindness4 ,franco-,british ,exhibition-- ,gold ,medal for ,colour ,educator4 ,international ,medical ,congress-- ,bronze ,medal for ,tintometer as ,medical requisite4 ,royal ,sanitary ,institute-- ,silver ,medal for recent developments4 ,royal ,sanitary ,institute-- ,silver ,medal ,corbett's ,radiometer4 ,formal ,adoption of ,tintometer ,standards by-- ,the ,petroleum ,industry4 ,the ,massachusetts ,board of ,health4 ,the ,international ,association of ,leather ,trades ,chemists4 ,the ,inter-states ,cotton ,seed ,oil ,association4 ,the ,bureau of ,engraving and ,printing1 ,china4 ,in general use by the following ,industries-- ,brewing and ,malting4 ,tanning4 ,wine and ,spirit ,merchants4 ,dyeing and ,printing4 ,paint1 ,oil and ,varnish ,merchants4 ,millers4 ,water ,works ,chemists4 ,ceramic ,works4 ,for estimating per cent4 of ,carbon in ,steel4 ,for estimating per cent4 of ,ammonia4 ,for estimating ,colours for ,anthropological ,classifications4 ,for estimating ,smoke ,densities4 ,for estimating ,haemoglobin in the ,blood4 ,for estimating ,colour of ,whale ,oil1 etc41 etc4 ,,the ,,method4 ,the colour composition of any object may be measured by superimposing units of different colours until the colour of the object is matched4 ,a convenient apparatus is furnished for this purpose4 ,the composition of the colour is learned by merely reading the markings on the glasses4 ,it is of course necessary that in the isolation of colour rays1 some unit for measuring the intensity of both light and colour be established4 ,as will be explained later1 all such units are necessarily arbitrary4 ,in this method the unit has been established by taking the smallest amount of colour easily perceptible to the ordinary vision4 ,this unit or 8one0 is divided into tenths in the darker shades1 and hundredths in the lighter scale4 ,one one-hundredth is the smallest amount of colour measurable by a normal trained vision4 ,when equivalent units in the three colours are superimposed1 their equivalent value 7not their aggregate value7 represents so much white light absorbed4 ,for instance1 #b ,r4 #b ,y4 #b ,b4 absorbs two units of white light4 ,when the absorptive power of the colour standards is less than the intensity of the light1 associated white light remains4 ,,joseph ,w4 ,,lovibond4 ,the ,colour ,laboratories1 ,salisbury4 ,december1 #aiad4 ,light and ,colour ,theories ,,chapter ,i4 ,introduction4 ,it may at first appear strange that colour1 one of the most important indices of value in the ,arts1 ,manufactures1 and ,natural ,products1 should have no common nomenclature or reliable standard for reference1 the reproduction of a given colour depending for exactitude on the memory of a sensation2 whereas this branch of science requires a physical means of recording a colour1 with a power of recovery4 ,it remains to be shown that this power of record and recovery is possible1 and depends only on the observance of a few simple natural laws easy of application4 ,the study of colour is carried on by two principal methods3 the spectroscopic1 where the colours are partially separated as a continuous band by a regular variation in their indices of refraction1 the colours gradually merging into each other by overlapping in opposite directions2 or by absorption1 where a colour is developed by absorbing its complementary1 and is isolated as a single or complex colour4 ,this latter is nature's own method4 ,it is necessary to touch on some theoretical differences which exist between ,scientists and ,artists1 as to which are ,primary colours1 as confusion of this character retards investigation4 ,scientists adopt ,red1 ,green1 and ,violet as ,primaries1 regarding all other colours as mixtures of these2 whilst ,artists and ,colourists adopt ,red1 ,yellow and ,blue as the ,primaries1 and all other colours as made from them4 ,the theory of the ,scientists is based on the phenomena developed by mixing coloured lights taken from different parts of the spectrum4 ,this is a method of synthesis1 each added colour being a progressive stage towards the complexity of white light4 ,in this case the colour developed is that of the preponderating ray of a complex beam4 ,the theory of the ,artists is based on the phenomena developed by mixed pigments4 ,this is a method of analysis1 tending towards ray simplicity1 each added pigment reducing the complexity of the colour developed by its power of selective absorption4 ,the theoretical differences between the two schools appear to have arisen from supposing that a given colour developed by the two methods should correspond2 but considering the differences in their ray composition1 this would be impossible1 for although both may be describable by one general colour term1 as for instance a ,red1 they would be of two varieties4 ,it remains to be shown that one theory may cover both sets of phenomena4 ,the ,red1 ,green1 and ,violet theory appears to be based on two principal assumptions3 first that there are only three fundamental colours2 and second that the rays taken from different colour areas are pure colours4 ,both assumptions are open to question4 ,in regard to the first1 there is no difficulty in isolating six colours2 and as to the second1 it can be demonstrated that the colours do overlap in every part1 with a double overlapping in the middle colours1 and are therefore not simple but complex4 ,,past ,,theories4 ,in a work of this nature it is unnecessary to deal minutely with the theories which have been adopted from time to time since ,newton's discovery of the continuous spectrum4 ,it will1 however1 be useful to touch on the principal points where theorists are agreed1 and also on some of their points of difference1 the latter in order to find1 if possible1 the causes of their difference4 ,,table ,i4 ---------------------------------------- ------------------------------ ,no4 of ,primary ,colours4 ,rays4 ---------------------------------------- ------------------------------ ,newton 7later7 #g ,red1 ,orange1 ,yellow1 ,green1 ,blue1 ,indigo1 ,violet ,werner #f ,red1 ,orange1 ,yellow1 ,green1 ,blue1 ,violet ,newton and ,helmholtz #e ,red1 ,yellow1 ,green1 ,blue1 ,violet 7early7 ,hering #d ,red1 ,yellow1 ,green1 ,blue ,chevieul1 ,brewster1 ,hay1 ,redgrave1 ,field #c ,red1 ,yellow1 ,blue ,young1 ,helmholtz 7later7 #c ,red1 ,green1 ,violet ---------------------------------------- ------------------------------ ,note to ,plate ,i4 ,the respective positions of the primaries of each theory in regard to the whole cycle of distinguishable colours are illustrated above1 and the primaries of each theory are shown in their several spectrum positions1 the spectrum being shown as bent in circular form4 ,the six principal theories of primary colours are given in ,table ,i1 and illustrated on ,plate ,i1 with the names of the primaries of each theory opposite the names of some of their principal advocates4 ,it should not be forgotten when comparing these wide divergences1 that each theory has been the result of experimental evidence1 in what was1 at the time1 and remains up to the present1 a new and progressive branch of science4 ,they agree that the spectrum colours are purer than the pigmentary colours1 and that by reason of their being referable to wave length positions1 they are most adaptable as standards of colour4 ,there has also been common agreement that certain colours are primaries1 and that all other colours are mixtures of these1 but there has been wide divergence as to their number and even the colours themselves4 ,illustration3 ,,plate ,i ,,illustrating ,,the ,,position ,,of ,,the ,,primaries ,,in ,,relation ,,to ,,the ,,colours ,,required ,,to ,,be ,,produced ,,by ,,the ,,theoretical ,,mixtures ,,and ,,also ,,in ,,relation ,,to ,,the ,,chromatic ,,circle4 ,a ,,seven ,,ray ,,theory4 ,,newton4 ,a ,,six ,,ray ,,theory4 ,,werner4 ,a ,,five ,,ray ,,theory4 ,,newton 7,early74 ,,helmholtz 7,early74 ,a ,,four ,,ray ,,theory4 ,,hering4 ,a ,,three ,,ray ,,theory4 ,,chevreul4 ,,brewster4 ,,hay4 ,,redgrave4 ,,field4 ,a ,,three ,,ray ,,theory4 ,,young-,,helmholtz4 ,to face page #d4 ,lovibond1 ,colour ,theories4 ,,chapter ,,ii4 ,evolution of the ,method4 ,the writer was formerly a brewer1 and this work had its origin in an observation that the finest flavour in beer was always associated with a colour technically called 8golden amber10 and that1 as the flavour deteriorated1 so the colour assumed a reddish hue4 ,it was these variations in tint that suggested the idea of colour standards as a reliable means of reference4 ,the first experiments were made with coloured liquids in test tubes of equal diameter1 and by these means some useful information was obtained2 but as the liquids soon changed colour1 frequent renewals were necessary1 and there was always a difficulty and uncertainty in their exact reproduction4 ,to obviate this1 glass in different colours was tried1 and long rectangular wedges with regularly graded tapers were ground and polished for standards1 whilst correspondingly tapered glass vessels were made for the beers4 ,these were arranged to work side by side1 and perpendicularly1 before two apertures of an optical instrument1 which gave a simultaneous view of both4 ,the apertures were provided with a fixed centre line1 to facilitate the reading off of comparisons of thickness4 ,there was no difficulty in obtaining glass which approximated to the required colour when used in one thickness only4 ,but as thickness varied1 the test no longer held good for both standards1 their rates of colour change being different1 making the method unreliable4#a #a ,it was afterwards found that these colour changes through variations of intensities were due to a natural law to be described under the heading of 8,specific colour40 7,see page #cb47 ,the system about to be described is one of analytical absorption1 and has been published from time to time in the form of papers1 read before ,societies interested in the question of colour standardization2 as also in two descriptive works by the present writer4 ,the earlier works were necessarily fragmentary1 but gathered system as the subject progressed4 ,at an early stage in the investigations it was realized that the handbooks of the period dealt largely with theoretical differences which were of little service to the technical worker4 ,under these circumstances the writer applied for advice to the late ,mr4 ,browning of the ,strand1 who gave it as his opinion that no work existed which could be of service to the writer4 ,all that could be done was to go on until something should be arrived at4 ,on this1 all theoretical reading was put aside1 and the work proceeded on the simple lines of observing1 recording1 and classifying experimental facts4 ,in working with glass of different colours it was found that some combinations developed colour1 whilst other combinations destroyed it4 ,this suggested the probability of a governing natural law2 and experimental work was undertaken in the hope of discovering it4 ,the result was the construction of a mechanical scale of colour standards1 which are now in use in over one thousand laboratories1 and no question of their practical accuracy arises4 ,the principal conditions for ensuring accuracy and constancy of results are embodied in the following code of nine precautions1 which have been published for nearly twenty years without being disputed4 ,they may therefore be considered as governing laws1 at least for the present4 ,the colour theory adopted for these ,governing ,laws has grown out of a series of experimental facts capable of demonstration1 and is summed up in the following code of nine ,laws4 ,laws #a1 #b1 and #c relate to ,white and ,coloured ,light1 and are as follows3-- #a4 ,normal white light is made up of the six colour rays1 ,red1 ,orange1 ,yellow1 ,green1 ,blue and ,violet in equal proportions4 ,when these rays are in unequal proportions the light is abnormal and coloured4 #b4 ,the particular colour of an abnormal beam is that of the one preponderating ray1 if the colour be simple1 or of the two preponderating rays if the colour be complex4 ,the depth of colour is in proportion to the preponderance4 #c4 ,the rays of a direct light are in a different condition to the same rays after diffusion1 and give rise to a different set of colour phenomena4 ,laws #d1 #e1 #f1 and #g deal with ,the ,limitations of the ,vision to appreciate ,colour4 #d4 ,the vision is not simultaneously sensitive to more than two colours in the same beam of light4 ,the colour of any other abnormal ray is merged in the luminosity of the beam4 #e4 ,the two colours to which the vision is simultaneously sensitive are always adjacent in their spectrum order1 ,red and ,violet being considered adjacent for this purpose4 #f4 ,the vision is unable to appreciate colour in an abnormal beam outside certain limits1 from two causes3 7a7 ,the colour of an abnormal beam may be masked to the vision from excess of luminosity4 7b7 ,the luminous intensity of the abnormal beam may be too low to excite definite colour sensations4 #g4 ,the vision has a varying rate of appreciation for different colours by time1 the lowest being for red4 ,the rate increases in rapidity through the spectrum1 until the maximum rate is reached with violet4 ,and since this varying rate necessitates a time limit for critical observations1 five seconds has been adopted as the limit1 no variations being perceptible in that time4 ,laws #h and #i relate to ,colour ,constants4 #h4 ,the colour of a given substance of a given thickness is constant so long as the substance itself1 and the conditions of observation1 remain unaltered4 #i4 ,every definite substance has its own specific rate of colour development for regularly increasing thicknesses4 ,,chapter ,,iii4 ,evolution of the ,unit4 ,the dimensions of the light and colour unit here adopted1 together with the scales of division1 were in the first instance physiological1 depending entirely on the skill of normal visions for exactitude4 ,the co-relation of equal values in the different colour scales1 was secured by an elaborate system of cross-checking1 rendered necessary because the establishment of a perfectly colourless neutral tint unit1 demanded an exact balance in values of the different colour scales4 ,these scales have stood the test of many years' work by many observers1 and in no case has any alteration been required4 ,the original set is still in use4 ,the first point which required consideration after the want of standard colour scales was realized1 was the basis and dimensions of the unit4 ,so far as the writer knew there was no published information bearing on this which could be used as a guide4 ,several arbitrary scales for specific purposes had already been constructed by selecting a colour depth which could easily be distinguished1 calling it a unit1 and scaling it by duplicating and subdividing4 ,this course was adopted with a coloured glass which approximately matched ,ales and ,malt solutions1 and another which matched ,nesslerized ,ammonia solutions4 ,no insuperable difficulty occurred in constructing scales available for quantitative work in these two instances4 ,the intensity of the colour unit for these arbitrary scales1 was that which appeared to be most convenient for the purpose required1 but the several scales had no common basis4 ,the unit was physiological1 and the exactitude of the scales depended entirely on the skill of the vision for discriminating small differences4 ,as the writer's experimental work progressed1 it became evident that red1 yellow1 and blue were the only colours suitable for systematic work4 ,the superimposition of any two1 developed a third colour which apparently had no relation to either4 ,the superimposition of the third glass modified or destroyed all colour and reduced the amount of light4 ,this suggested the idea that if the three colours could be so balanced that the light transmitted was colourless1 it would be evidence of equivalence of intensity in the individual colours4 ,the real difficulty was in obtaining this equivalence1 because a balance which transmitted a neutral tint by one light developed colour by another4 ,this necessitated the selection of a standard light4 ,the light finally selected was that of a so-called sea fog1 away from the contaminating influence of towns4 ,the white fog of ,salisbury ,plain was used as being most available4 ,it required two years' work to establish equivalence in the unit4 ,illustration3 ,,plate ,,ii ,,nine ,,circles ,,illustrating ,,the ,,analysis ,,of ,a ,,beam ,,of ,,white ,,light ,,into ,,the ,,six ,,composing ,,colours ,,by ,,the ,,absorptive ,,method ,a4 ,,white ,,light ,b4 ,,divided ,,into ,,chromatic ,,equivalents ,c4 ,,wholly ,,absorbed ,,colours ,,of ,,the ,,first ,,division ,,developed ,,by ,,the ,,absorption ,,of ,,the ,,three ,,complimentaries #a #b #c ,,colours ,,of ,,the ,,second ,,division ,,developed ,,by ,,the ,,absorption ,,of ,,the ,,five ,,other ,,rays #d #e #f ,to face page #aa4 ,lovibond1 ,colour ,theories4 ,,chapter ,,iv4 ,derivation of ,colour from ,white ,light4 ,the method of analysing white light into its colour constituents by means of coloured glass absorbents of known intensity and purity1 is illustrated by the set of nine circles in ,plate ,,ii1 which demonstrate that colour is developed by the absorption of the complementary colour rays4 ,the ratios of transmission are equal4 ,in this set of illustrations the circles represent light of #bj units luminous intensity1 and the absorptive value of the three glass colours is each of #bj units1 therefore the whole of the light and colour energies are presumed to be dealt with4 ,in the first set of three circles1 ,a represents a beam of normal white light4 ,b a similar beam as divided into the six colour rays1 ,red1 ,orange1 ,yellow1 ,green1 ,blue and ,violet in equal proportions1 ,c as wholly absorbed by ,red1 ,yellow1 and ,blue glasses1 each of #bj units colour intensity4 ,figures #a1 #b and #c represent the specific action of ,red1 ,yellow1 and ,blue glass on the white light4 ,red absorbs ,yellow1 ,green and ,blue1 transmitting ,violet1 ,red and ,orange1 developing ,red only4 ,yellow absorbs ,blue1 ,violet1 and ,red1 transmitting ,orange1 ,yellow and ,green1 developing ,yellow only4 ,blue absorbs ,red1 ,orange and ,yellow1 transmitting ,green1 ,blue1 and ,violet1 developing ,blue only4 ,by this method of development1 ,red1 ,yellow or ,blue1 when seen alone are visually monochromatic1 although composite in structure1 each containing a group of three rays1 the middle ray alone exciting the colour sensation4 ,circles #d1 #e1 and #f illustrate the development of ,orange1 ,green and ,violet from the triad groups1 by intercepting the light with two glass colours4 ,circle #d1 ,red on ,yellow1 develops ,orange by absorbing ,yellow1 ,green1 ,blue1 ,violet and ,red4 ,circle #e1 ,yellow on ,blue1 develops ,green by absorbing ,blue1 ,violet1 ,red1 ,orange and ,yellow4 ,circle #f1 ,blue on ,red1 develops ,violet by absorbing ,red1 ,orange1 ,yellow1 ,green and ,blue4 ,by this method of demonstration the six colours fall naturally into two groups4 ,the first group includes ,red1 ,yellow1 and ,blue1 whilst the second group includes ,orange1 ,green1 and ,violet4 ,the colours of the second group1 ,orange1 ,green1 and ,violet1 are true monochromes1 each being isolated from the light1 by the absorption of the five other rays4 ,these illustrations deal with light and colour of #bj units intensity2#b as the intensity of the light here is exactly equal to the absorptive power of the standards1 no free light remains2 where the absorptive power of the colour standards is less than the light1 associated white light remains2 for instance1 if only one unit of colour was developed1 #ai units associated white light would remain4 #b ,for description of the light and colour units1 refer to chap4 ,,iii1 page #i4 ,illustration3 ,,plate ,,iii ,to face page #ac4 ,lovibond1 ,colour ,theories4 ,this method of colour development by analytical absorption is further illustrated by ,plate ,,iii1 showing the effect of superimposition of the three colours in their several combinations as intercepting a beam of white light4 ,not all lights which appear white to the vision are truly normal white2 colour may be masked by excess of luminosity1 and only become evident when the luminosity has been reduced1 by placing neutral tint standards between the light and the observer4 ,direct sunlight1 and some artificial lights1 are instances4 7,law #f 7a7 page #h47 ,on the other hand1 an abnormal light may be too low for the vision to discriminate colour4 ,this may be observed in nature by the gradual loss of colour in flowers1 etc41 in the waning intensities of evening light4 ,the order of their disappearance is shown in ,chart ,i4 ,,chapter ,v4 ,standard ,white ,light4 ,the colour of a substance is determined by the ray composition of the light it reflects1 or transmits to the vision1 the colour would therefore vary with every change in the ray proportions of the incident light2 it follows that constancy in colour measurement can only be obtained by a colourless light4 ,up to the present diffused daylight is the only light which complies with the condition of ray equality4 ,the absolute equality of the six spectrum colours may be difficult to establish in any light1 and their constancy in equivalence under varying light intensities may be open to argument4 ,but1 as everyday work is carried on mainly under daylight conditions1 and as the vision is the final arbiter for colour work1 theoretical questions outside the discriminating power of the vision1 need be no bar to the establishment of a working standard white light2 and in saying that diffused daylight is normal white1 it is only intended to mean3 ,in so far as a normal vision can determine4 ,apart from any theoretical explanation it is an experimental fact1 that the abnormal rays of direct sunlight1 and some artificial lights1 may be so modified by diffusion as to be available for a limited range of colour work4 ,in the case of diffused north sunlight1 when taken from opposite the sun's meridian1 the modification is sufficient to make it available as a standard white light4 ,in the case of artificial lights1 their use is1 as yet1 limited to visual matching 7not recording7 and arbitrary comparisons4 ,,the ,,black ,,unit4 ,ideal black is total absence of light1 and can only be realized as a sensation1 in the presence of light1 which may however be in contrast or in association4 ,the nearest approach to ideal black by contrast1 is to view a hole in a box with a blackened interior1 so arranged that no light entering the hole1 can be reflected back to the vision3 in this way associated light1 if not entirely absent1 is reduced to a minimum and total darkness is practically realized by the vision in contrast with the surrounding light4 ,pigmentary black viewed under diffused daylight conditions is always associated with white light1 as no substance1 however black it may be1 absorbs all the impinging light2 as examples1 the following measurements of three white and three black pigments were made at an angle of #de degrees with a light intensity of #be units4 ,this is a true quantitative analysis of the #be units of white light after reflection from the black pigments4 ,the black units represent the proportion of white light absorbed1 whilst the beams reflected from the pigments consist of the colour values developed which are associated with the unabsorbed white light4 ,,table ,,ii4 ---------------------------------------- --------------------- ,lime ,blue ,lamp ,ivory ,zinc ,white ,sulphate,black ,black ,black ,white ,lead ---------------------------------------- --------------------- ,standard light units #bej ---------------------- ,black units 7light absorbed7 #ij #ib #ib -- #jh ,violet units 7colour developed7 #bb #ad #ad -- -- ,blue units 7colour developed7 #aj #ai #d #ja #je ,green units 7colour developed7 -- -- -- -- #jg ,associated white light #abh #abe #adj #bdii #bdhj ---------------------------------------- --------------------- ,totals #bej #bej #bej #bej #bej #bej ---------------------------------------- --------------------- ,the analyses demonstrate that black is not itself an active energy analogous to colour1 but is a minus quantity distinguishable by contrast with the original light4 ,the reflected beam consists of the colour developed1 associated with the residue of unaltered light4 ,note4--,suitable proportions of ,violet and ,blue give character and value to black1 whilst ,orange and ,yellow are less pleasing as tending to rustiness4 ,,chapter ,,vi4 ,qualitative ,colour ,nomenclature4 ,,simple ,,colours4 ,the vision can separate six monochromatic colours from a beam of white light1 therefore in practical work six must be dealt with1 no matter how they may be theoretically accounted for4 ,they naturally take the accepted spectrum names and symbols already in use4 ,to these are added two other terms1 ,bk4 to signify black1 and ,l4 for light2 these terms deal with the brightness1 or dinginess1 of a colour4 ,simple ,terms4 ,symbols4 ,red ,r ,orange ,o ,yellow ,y ,green ,g ,blue ,b ,violet ,v ,black ,bk ,white ,l ,,complex ,,colours4 ,the order of the association of simple colours to form complex1 is governed by two factors4 ,the first is a physiological limitation of the vision1 which is unable to simultaneously distinguish more than two colours1 in the same beam of light1 this limits the most complex colour to two colour names4 ,the second limitation is one of association1 based on the experimental fact1 that the particular two must be adjacent in their spectrum order1 spectrum red and violet being considered adjacent for this purpose4 ,under these conditions1 any given colour must be either a monochrome1 or a bichrome1 and all complex colours must be bichromes4 ,therefore the only possible combinations are as follows3-- ,red and ,orange ,orange ,yellow ,yellow ,blue ,blue ,green ,green ,violet ,violet ,red ,the classified order of associating symbols for describing the components of the whole range of distinguishable colours is set out in the following tables3-- -------------------------------------- ,monochromes ,monochromes ,monochromes of a ,standard,brighter than,duller than ,brightness4 ,standards4 ,standards4 -------------------------------------- ,r4 ,r4 ,l4 ,r4 ,bk4 ,o4 ,o4 ,l4 ,o4 ,bk4 ,y4 ,y4 ,l4 ,y4 ,bk4 ,g4 ,g4 ,l4 ,g4 ,bk4 ,b4 ,b4 ,l4 ,b4 ,bk4 ,v4 ,v4 ,l4 ,v4 ,bk4 -------------------------------------- ,illustration ,the separation of the six monochromatic sensations from a point of white light1 and the formation of binary sensations by the combination of adjacent colours1 is graphically illustrated in the above diagram4 ,in order to make the qualitative symbols quantitative it is only necessary to add the numerical unit value to each factor as found by direct experiment4 ,,chapter ,,vii4 ,quantitative ,colour ,nomenclature4 ,,the ,,glass ,,standard ,,scales4 ,at an early stage of the investigation1 it was found that coloured glass gave better results than coloured solutions1 and that ,red1 ,yellow1 and ,blue1 were the only colours suitable for systematic work2 it was also found that any colour could be produced by their combination4 ,as already described arbitrary scales were first used in many colours1 but were superseded by these three1 which1 when graded into scales of equivalent value1 were found to cover all daylight colours4 ,upon this evidence1 scales of red1 yellow and blue were constructed of glass slips1 each scale being all of one colour1 with a regular variation of intensity from #jja to #bjj units1 equal units of the three scales being in equivalence with each other4 ,the dimensions of the unit are necessarily arbitrary1 but the scales comply with the essentials of a scientific standard1 in that the divisions are equal1 and the unit recoverable4 ,the equality of the unit divisions in the scales1 is demonstrated by a system of cross-checking4 ,the test of colour equivalence has already been described on pages #aj and #bh4 ,the power of recovering the unit1 is by co-relation to well-known physical colour constants1 such as is easily obtained by definite intensities of percentage solutions1 of selected pure chemical compounds in distilled water1 at standard temperatures4 ,for example1 a one per cent4 solution of pure crystallized copper sulphate ,c#b,,so#de;,h#b,o at #fj ,f4 when viewed in the optical instrument in a #a-;inch stratum1 must be matched by a combination of ,yellow #aeh and ,blue #aee4 ,the inch of distilled water itself constitutes very little of this colour2 the colour of distilled water is remarkably uniform1 and might almost be taken as a colour constant1 thus3 ,a #b-;foot stratum is matched by ,yellow #ja and ,blue #jcd1 a #d-;foot stratum by ,yellow #aj and ,blue #ade4 ,a one per cent4 solution of ,nickel ,sulphate ,ni,s,o#dg;,h#b,o1 tem4 #fj ,f4 in a #b-;inch stratum must be matched by #bb ,blue and #bj ,yellow units4 ,a one per cent4 solution of ,potassium ,bichromate ,k#b;,cr#b,o1 ,tem4 #fj and in a #b-;inch stratum after being dulled by #je neutral tint units must be matched by #cdj yellow and #if red units4 ,,method ,,of ,,developing1 ,,measuring ,,and ,,naming ,,colour4 ,the single sensation colours1 ,red1 ,yellow and ,blue1 are matchable by a single glass from the corresponding colour scale2 the depth of colour is directly indicated by the value of the glass used4 ,the single sensation colours1 ,orange1 ,green and ,violet1 are matchable by a combination of equal units1 from two of the standard scales1 the depth of colour is directly indicated by the unit value of either of the glasses1 thus3 #bj ,blue #bj ,red develop #bj units ,violet4 ,a given neutral grey is matchable by a combination of equal units from the three standard scales1 the depth of grey1 is directly indicated by the unit value on either of the glasses used1 thus3-- #cj ,red #cj yellow #cj blue develop #cj units neutral tint4 ,the complex colour sensations1 red and yellow oranges1 yellow and blue greens1 blue and red violets are matchable by unequal glasses from two of the standard scales2 the colour developed is not directly indicated by the unit value of the glasses1 but is recorded by means of an equation1 the first half of which contains the separate values of the glasses used1 and the second half the names and the depth of the colours they transmit4 ,for instance-- ,the equation of a colour matched by #agj red and #bf blue units1 is as follows3-- ,standard ,glasses4 ,colour ,developed4 ,red4 ,blue4 ,violet4 ,red4 #agj #bf #bf #add ,the colour developed is a red violet in these proportions4 ,a colour matched by ,standard ,glasses4 ,colour ,developed4 ,red4 ,yellow4 ,orange4 ,red4 #ajj #cj #cj #gj ,the colour developed is a red orange in these proportions4 ,a colour matched by ,standard ,glasses4 ,colour ,developed4 ,yellow4 ,blue4 ,green4 ,yellow4 #cj #ae #ae #ae ,the colour developed is a yellow green in these proportions4 ,a colour matched by ,standard ,glasses4 ,colour ,developed4 ,blue4 ,red4 ,blue4 ,violet4 #fj #ah #db #ah ,the colour developed is a blue violet in these proportions4 ,the standard glass colours are necessarily of a given brightness1 and colours for measurement may be either brighter1 or sadder than the standards4 ,a given complex colour of less than glass standard brightness1 is matchable by unequal numbers from the three standard scales2 the smallest unit value always represents the 8black10 or neutral unit factor4 ,the equation is as follows3-- ,a colour matched by ,standard ,glasses4 ,colour ,developed4 ,red4 ,yellow4 ,blue4 ,neutral ,tint4 ,green4 ,blue4 #aj #cj #ij #aj #bj #fj ,the colour is a blue green1 in the proportion of six to two1 saddened by one of neutral tint4 ,a given complex colour of greater brightness than the glass standards1 is first dulled by the interception of neutral tint units1 until measurable in the manner described above2 the intercepting glasses represent the unit value of excess of brightness1 and is shown in the equation as light units1 for instance-- ,standard ,glasses4 ,colour ,developed4 ,neutral ,tint4 ,yellow4 ,blue4 ,light4 ,green4 ,yellow4 #ae #ge #je #ae #je #gj ,the colour is a yellow green in the proportions of #gj of yellow1 to #je of green1 and #ae brighter than the standards4 ,every daylight colour being thus measurable by a suitable combination of standard glasses1 with or without the addition of a ,light1 or a ,neutral ,tint factor1 it follows that any colour can be described both qualitatively1 and quantitatively1 in terms of the colour sensations yielded by the standard glasses and their combination4 ,the distinct colour sensations are those1 which1 by common consent are known as ,red1 ,yellow1 ,blue1 ,orange1 ,green and ,violet1 and they are yielded by single glasses1 or by pairs as already described2 all colours therefore fall into the following categories3-- ,a4--,single colour sensations3-- #a4 ,transmitted by single glass standards3 ,red4 ,yellow4 ,blue4 #b4 ,transmitted by equivalent pairs of standard glasses3 ,orange4 ,green4 ,violet4 ,b4--,double colour sensations transmitted by unequal pairs of standard glasses4 ,red orange1 transmitted by unequal units of red and yellow1 red preponderating4 ,yellow orange1 transmitted by unequal units of red and yellow1 yellow preponderating4 ,yellow green1 transmitted by unequal units of yellow and blue1 yellow preponderating4 ,blue green1 transmitted by unequal units of yellow and blue1 blue preponderating4 ,blue violet1 transmitted by unequal units of blue and red1 blue preponderating4 ,red violet1 transmitted by unequal units of blue and red1 red preponderating4 ,c4--,any of the above colours with the addition or subtraction of neutral tint4 ,neutral tint itself1 is transmitted by a combination of equal units of the standard glasses1 thus three units red1 yellow and blue1 when superposed1 transmit three units neutral tint4 ,,examples4 ,three units red1 of standard brightness1 completely describes a colour matched by a red glass of three units1 and is denoted ,r4 #cj ,three units red saddened by one neutral tint1 completely describes a colour matched by a red glass standard of four units red1 combined with a blue and yellow of one unit each1 and is denoted ,r4 #cj ,n4,t4 #aj ,a given red of three units1 which is one unit brighter than standards1 after having been saddened by one unit each of red1 yellow and blue1 is matched by three units of red and is correctly described by ,red #cj ,light #aj ,three units of violet1 of standard brightness1 is matched by a red and a blue glass of three units1 and is correctly described by ,v4 #cj ,three units of orange1 of standard brightness1 is matched by a red and a yellow glass of three units1 and is correctly described by ,o4 #cj ,a binary red violet of standard brightness1 in which red preponderates by one unit1 is matched by four units red1 and a blue of three units1 and is correctly described by ,r4 #aj ,v4 #cj ,a binary red orange1 of standard brightness1 in which orange preponderates by three units1 is matched by red four and yellow three units1 and is correctly described by ,r4 #aj ,o4 #cj ,a red orange1 of less than standard brightness by one unit1 in which orange preponderates by three units1 is matched by a red five1 yellow four1 blue one1 and is correctly described by ,r4 #ai ,o4 #cj ,n4,t4 #aj ,a red violet1 in which red preponderates by one unit1 and is one unit brighter than standard1 is first dulled by one unit red1 yellow and blue1 and then matched by four red and three blue1 and is correctly described by ,r4 #aj ,v4 #cj ,light #aj ,a red orange1 in which red preponderates by one unit1 and is one unit brighter than standard1 is first dulled by one red1 yellow and blue1 and then matched by four red1 and three yellow1 and is correctly described by ,r4 #aj ,o4 #cj ,light #aj ,,chapter ,,viii4 ,the ,colour ,scales4 ,a normal vision under ordinary conditions1 has no hesitation in correctly naming the sensations produced by the triad groups red1 yellow and blue1 or by the single rays orange1 green and violet4 ,it can also correctly describe a complex colour sensation1 by naming the two associated colours1 such as red orange1 yellow orange1 blue green1 blue violet1 etc42 but when called upon to decide differences of colour depth1 it can only do so by using arbitrary terms of no precise scientific value1 such as light1 medium1 dark1 etc4 ,this deficiency is because the vision has in itself no arrangement for the quantitative definition of colour depth4 ,this want can only be met by co-relating colour sensations1 to some physical colour constants4 ,this co-relation has now been effected by a series of glass standard colour scales1 which are numerically graded for colour depth1 the scales themselves being colour constants by co-relation to percentage solutions1 of such coloured chemicals1 as copper sulphate1 nickel sulphate1 potassium permanganate1 etc4 ,these substances as well as many others1 are always available for checking the constancy of the scales1 or for recovering the unit if lost4 ,as already mentioned1 the system of taper scales proved to be useless for the purpose1 not only because the rate of colour increase was never in proportion to the rate of thickness increase1 but also because no two substances are equal in this respect1 each having a rate specific to itself4 ,the prismatic spectrum colours were not available for several reasons1 first as being unsuitable for critical comparisons under daylight conditions1 as being too weak except 8in camera02 also they were found to be too crowded for the separation of a working area of monochromatic colour1 and some corrections would have been necessary for variation in the refractions of different colour rays4 ,this is more fully dealt with under the heading of ,the ,spectrum in relation to ,colour ,standardization1 page #cf4 ,,the ,,equivalence ,,of ,,the ,,colour ,,scales4 ,the method employed for obtaining equality of the unit divisions1 and colour equivalence between the different scales was as follows3-- ,two slips of red glass in a light shade were made exactly equal in colour1 and considered as initial units2 these were then superimposed and matched by a single glass1 which was then considered as of two units1 this and one of the initial units were superimposed1 and matched by a single glass of three colour units1 and so on1 until a progressive red scale was constructed1 ranging in intensity from #ja to #bj units4#c #c ,it was found that the superimposition of two glasses did not visually disturb equivalence1 therefore only two glasses were used for each observation in constructing the scales4 ,the yellow and blue scales1 were similarly constructed1 taking care that their similar unit values were in colour equivalence with the red units1 the test of equivalence being1 that when equal units of the three scales were superimposed against a normal white light1 a neutral grey was transmitted1 in which no trace of colour could be perceived by the common consent of the whole staff of trained observers4 ,the scales were then considered as in colour equivalence with each other4 ,the system of cross-checking was so elaborate1 that after the equivalence of the first unit was established1 nearly four years was occupied in the work before the scales were passed as satisfactory4 ,it may be urged that the unit is arbitrary1 but this applies also to the unit of any other standard scale2 it is sufficient that the essentials of a philosophic scale are complied with1 in that the divisions are equal1 and the unit recoverable4 ,illustration3 ,,plate ,,iv ,,comparison ,,curves ,,of ,,healthy ,,human ,,blood ,,with ,,the ,,blood ,,of ,,lower ,,animals4 ,to face page #ca4 ,lovibond1 ,colour ,theories4 ,,chapter ,,ix4 ,colour ,charts4 ,a colour chart is constructed by placing two colour scales at right angles to each other1 with their zeros at the angle4 ,a measured simple colour1 finds its position directly on its corresponding colour scale at the point of its measured value4 ,a measured complex colour1 finds its position within the angle1 at that point where perpendiculars drawn through the two colour values meet4 ,the above statements are complete only for colours of standard brightness1 should the colour be brighter or duller than standards1 a light factor is necessary1 the value of which is furnished by the measurement itself1 and must be written in numerals near the colour point4 ,by this method the chart position of even the most complicated colour is indicated by a single point which is determined by the analytical value of the composing factors4 ,,examples4 ,simple ,colour of ,complex ,colour ,standard of ,standard ,brightness4 ,brightness4 #c ,red4 #f ,blue1 #aj ,violet4 ,simple ,colour ,complex ,colour ,brighter than ,duller than ,standards4 ,standards4 #g ,yellow1 ,red #f1 ,orange #e1 ,light #b ,black #b4 ,the number of complex colour charts is limited to the six represented in ,fig4 #a as lying in their order on a continuous spectrum4 ,the red and violet mixtures having no visible spectrum position are represented in the ultra violet4 ,the ordinates of the charts are made by erecting the overlying red1 yellow and blue scales as perpendiculars4 ,illustration3 ,fig4 #a4 ,the information to be obtained by charting measured colour is more extensive than appears at first sight1 as by varying the character of the co-ordinates1 and charting suitable series of measurements1 new fields of investigation are opened1 thus throwing light on some hitherto obscure questions1 of which the following are some instances4 ,,specific ,,colour4 ,it has sometimes been assumed that colour increase was in direct ratio to intensity increase1 but this is never the case1 each substance has its own rate1 specific to itself4 ,it is conceivable that the colours of two substances may coincide at one point1 but as their densities increase1 or decrease1 their rates of change vary4 ,the term 8,specific ,colour0 is based on the experimental fact1 that the colour of a given substance is constant1 so long as the substance itself and the conditions of observation1 remain unaltered4 ,during experimental work a sufficient number of instances have accumulated to warrant the writer in advancing and using the term 8,specific ,colour0 as describing a new natural law1 as rigid in its application as that of 8,specific ,gravity0 or 8,specific ,heat40 ,illustration3 ,,plate ,v ,,absorption ,,curves ,,of ,,five ,,colour ,,constants4 ,to face page #cc4 ,lovibond1 ,colour ,theories4 ,when this principle is applied to the measurement of regularly increasing thicknesses1 curves of colour changes can be established1 which are specific for the substance in question1 and afford a certain means of identifying similar substances in future4 ,this is effected by varying the nature of the co-ordinates1 making the ordinates to represent the tintometrical scale of colour units irrespective of colour1 whilst the abscissae represent the scale of increasing thicknesses4 ,then by plotting the separate factors of each measurement according to their unit values1 a series of curves is established1 specific to the substance in question1 and applicable to none other4 ,we have now two systems of charting colour1 in the first1 the complete sensation is represented by a single point1 as in ,plate ,,iv4 ,in the second1 each factor is represented by a separate point1 and by connecting points of similar colours1 a series of curves is established which represents a quantitative analysis of the progressive colour development1 as in ,plate ,v4 ,,chapter ,x4 ,representations of ,colour in ,space of ,three ,dimensions4 ,the relations of the different colours to one another1 and to neutral tint are1 perhaps1 best represented to the mind by a solid model1 or by reference to three co-ordinate axes1 as employed in solid geometry 7see ,fig4 #b74 ,illustration3 ,fig4 #b4 ,let the three adjacent edges ,,or1 ,,ob1 ,,oy1 of the above cube be three axes1 along which are measured degrees of ,red1 ,yellow and ,blue respectively1 starting from the origin ,o4 ,every point in space on the positive side of this origin will then represent a conceivable colour1 the constituents of which in degrees of red1 yellow and blue are measured by the three co-ordinates of the points4 ,pure reds lie all along the axis ,,or1 pure yellows on the axis ,,oy1 and pure blues on the axis ,,ob4 ,all normal oranges1 normal greens1 and normal violets lie on the diagonals of the faces of the cubes ,,oo#a1 ,,og1 ,,ov respectively4 ,pure neutral tints lie on the diagonal ,,on of the cube1 equally inclined to the three principal axes4 ,red violets will be found on the plane ,,rob1 between ,,ov and ,,or4 ,blue violets on the same plane between ,,ov and ,,ob4 8,saddened0 red violets all within the wedge or open space enclosed by the three planes1 whose boundaries are ,,ob1 ,,ov1 ,,on4 ,the other colours1 red and yellow oranges1 blue and yellow greens1 pure and saddened1 are found in corresponding positions in relation to the other cases4#d #d ,this method of illustration was suggested by ,dr4 ,herbert ,munro4 ,,chapter ,,xi4 ,the ,spectrum in relation to ,colour ,standardization4 ,the spectrum has naturally been considered as a suitable source for colour standards1 but the power of analysing has disclosed some difficulties1 which have yet to be overcome4 ,concerning the prismatic spectrum1 there has always been a difficulty in apportioning the different colours to specific areas1 and further1 before this spectrum is available for colour standardization1 some method of correction for the unequal distribution of colours must be devised4 ,neither of these difficulties occur in the use of the diffraction spectrum1 where the pure colours are apportioned by ,professor ,rood from ,a to ,h in the manner shown in table on next page4 ,professor ,rood further divides the spectrum from ,a to ,h into #ajj equal divisions1 allotting #bj unit divisions of #gb1gaf wave lengths to the space between each two colour lines4 ,this allots a space of #c1fce ,w4,l4 to each unit division1 as shown in ,table ,,iii4 ,,table ,,iii4 ---------------------------------------- --------------------- ,no4 of ,wave ,lengths ,w4,l4,k4 ,wave ,length ,position4 from ,division per ,colour ,division between each4 ---------------------------------------- --------------------- #gfj1djj ,a4 ,red #gfj1djj ----------------------- #gb1gag #bj #c1fce ,orange #fhg1fhc ----------------------- #gb1gaf #bj #c1fce ,yellow #fad1ifg ----------------------- #gb1gaf #bj #c1fce ,green #edb1bea ----------------------- #gb1gaf #bj #c1fce ,blue #dfi1ece ----------------------- #gb1gaf #bj #c1fce #cif1hai ,h4 ,violet #cif1hai ---------------------------------------- --------------------- #cfc1eha ,total ,w4,l4 between ,a4 ,h4 #cfc1eha #ajj ---------------------------------------- ---------------------- ,having provided equal wave length positions for the six pure colours1 the intermediate colours are necessarily binaries in definite proportions1 accounted for by a regular overlapping of two bounding colours in opposite directions from zero to #bj1 as shown in the following table from ,red to ,orange1 representing the space between these two pure colours4 ,red #bj #ai #ah #ag #af #ae #ad #ac #ab #aa #aj #i #h #g #f #e #d #c #b #a #j ,w4,l ,w4,l #fhg1 #gfj1 #j #a #b #c #d #e #f #g #h #i #aj #aa #ab #ac #ad #ae #af #ag #ah #ai #bj #fhc #djj ---------------------------------------- ---------------------- ,orange4 #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj #bj ,it follows1 that apart from the six monochromes1 all spectrum complex colours in a single wave length must be binaries1 whose united values equal #bj4 ,on comparing ,professor ,rood's scales of divisions with those of the tintometrical scales already described1 they appear to coincide in several particulars1 for instance3-- ,the monochromes correspond both in number and in name4 ,their positions in the scales correspond4 ,their unit divisions are equal in number1 and in dimensions4 ,their colour positions correspond1 when an artificial tintometrical spectrum is made by regularly overlapping monochromes4 ,it follows that when the two scales are superimposed as in ,plate ,v41 showing similar monochromes as lying in the same perpendicular1 the same wave length numbers apply to both2 concerning the dimensions between the monochromes1 the spaces occupied by #gb1gaf wave lengths between the spectrum monochromes1 also represent similar spaces in the tintometrical scales1 and one-twentieth of this #c1fce represents the space of a single unit in each case4 ,in connexion with these co-related dimensions1 some information is obtainable bearing on the limitation of a monochromatic vision for discriminating small colour differences4 ,under ordinary daylight conditions1 the unit in the lighter shades of the tintometrical scale is divided into #ajj fractional parts1 each fraction therefore represents a space occupied by thirty-six wave lengths in the spectrum scale4 ,this may be near the limit of dimension for monochromatic vision in such a gradually changing colour scale1 as that of the spectrum1 and may be some guide as to suitable slit areas in the synthetical building up of complex coloured light4 ,illustration3 ,,plate ,,vi ,,six ,,colour ,,charts ,,in ,,one ,,or ,,another ,,of ,,which ,,any ,,simple ,,or ,,complex ,,colour ,,finds ,a ,,definite ,,position4 ,to face page #ci4 ,lovibond1 ,colour ,theories4 ,in ,plate ,,vi4 are shown the six tintometrical colour charts1 as lying in their order on the tintometrical spectrum1 illustrating that any measured colour factor lies in a perpendicular drawn through both spectra1 and occupying the same wave length position1 and may therefore be designated by that wave length number4 ,this explanation is not intended to convey that the colour energies do not really overlap beyond the boundaries of the dual combinations1 but only that the vision is unable to distinguish as colour1 such overlapping if it exists4 ,,points ,,of ,,difference4 ,on further comparisons of the two scales there are some points of difference which have a bearing on their values as colour standards4 ,there is a variation in the length of the two scales1 the spectrum terminating at ,h1 whilst the tintometrical scale is extended to a sixth division in the region of the ultra violet1 showing overlapping combinations of ,red and ,violet1 strictly analogous to the overlapping binaries in the other five sections4 ,these red and violet combinations constitute one-sixth of the cycle of distinguishable colours1 and cannot be omitted in any system of colour standardization1 therefore their absence in the continuous spectrum is a drawback4 ,a second drawback1 is the limited number of spectrum complex colours1 in consequence of each colour being blended only with overlapping colour value1 which lies in its own wave length1 whereas in nature each colour may be blended with any value of the overlapping colour4 ,in the tintometrical standards1 similar effects are obtained by changing the value of the graded slips4 ,it is true1 that complex colours other than those in the same wave length1 may be developed by blending two colours from different parts of the spectrum1 but the ray proportions of colours so produced1 are necessarily more complex than those developed by specific absorption2 the first being a method of synthesis towards complexity1 and the second a method of analysis towards simplicity1 and although two colours so produced may be similar in name1 red for instance1 they must differ in character4 ,this view may tend to reconcile some of the theoretical differences between ,scientists and ,artists4 ,,the ,,ultra ,,violet ,,division4 ,the complete range of daylight colours not being fully comprised in a continuous spectrum1 may be considered as a cycle of radiant energies1 sensitive to the vision as colour1 which can be represented as a circle as in ,plate ,,vii4 ,the outer and broken circle represents a bent spectrum1 the unoccupied division corresponding in position with that of the red and violet mixtures in the complete cycle4 ,this arrangement does not alter the relative positions of the ,fraunhoper lines ,a1 ,b1 ,c1 ,d1 ,e1 ,f1 ,g and ,h in reference to either scale1 but1 it theoretically breaks that sequence of the successive wave lengths in the ,red ,violet which holds good in the other five divisions from ,a to ,h4 ,illustration3 ,,plate ,,vii ,to face page #dj4 ,lovibond1 ,colour ,theories4 ,in order to theoretically avoid this juxtaposition of wave length contrast1 it is only necessary to imagine that the violet energy beyond ,h in the ultra violet1 is overlapped by the infra red energy of a succeeding spectrum1 filling this section with a series of overlapping binaries analogous in wave length sequence to that of the other sections4 ,a ,,residual ,,red ,,ray4 ,apart from the colours of everyday life there is1 in sunlight and most direct artificial lights1 an additional red energy which differs materially from the red energy in diffused daylight4 ,it was first noticed whilst establishing the colour equivalence of the tintometrical light unit1 by developing a red sensation which disturbed constancy of reading under certain conditions of light4 ,so far as the writer knows1 this energy has never been investigated as separate from the other spectrum red4 ,the following observations must be considered as tentative only4 ,,some ,,properties4 ,it does not obey the laws of absorption which govern the red of diffused daylight4 ,when the six transparent pigmentary colours are illuminated by direct sunlight1 and viewed through a sufficient number of ,neutral ,tint units1 the colours all disappear1 all appearing red alike1 with only differences in luminosity4 ,the spectrum position of this red energy is in the ,a4 ,b4 region1 and further interception by ,neutral ,tint whilst narrowing the band1 intensifies the colour1 until obstructed by the large number of intercepting glass surfaces4 ,it has no photographic action on the six sensitised papers dealt with in the photographic section4 ,,light ,,intensities4 ,the apparatus for determining the unit values of light intensities in the following series of measurements1 consisted of a conical rectangular hopper tapering from #b feet to #b inches square4 ,this was adapted so that the light from the small end1 commanded the stage of the optical instrument sufficiently close to cut off outside light4 ,the wide end facing a north sky was adapted with sliding shutters1 to regulate the area of incident light2 of the six water-colour pigments which nearest corresponded to the standard colours1 washed to their full depth on ,whatman's paper1 six measurements were made4 ,these measurements are shown in ,table ,,iv1 and classified in ,table ,v4 ,it will be noted that the readings are constant for all the colours between #af and #bf units1 except a variation of light #ae in the #bd-;inch opening1 which is in effect as if the cone was not present1 and #b in the #h-;inch area of orange4 ,note4--,experiments in this branch give some information relating to the perception of colour under daylight conditions1 by limiting the range of intensities within which colour can be distinguished and differentiated1 whilst their separate photographic action 7page #dh7 suggests the impression that colour phenomena1 outside these limits1 may be a physiological expression of widely varying underlying energies4 ,,table ,,iv4 ---------------------------------------- ------------------------ ,square ,pigment4 ,inches ,light ,black4 ,red4 ,orange4 ,aperture4,intensity4 ---------------------------------------- ------------------------ ,carmine #b #aj #e #bjb #c ---- #d #aa #e #aia #d ---- #f #ad #df #ahie #ei ---- #h #af ---- #afi #aa ---- #aj #bj ---- #afi #aa ---- #ab #bb ---- #afi #aa ---- ,open #bf ---- #afi #aa ---- ---------------------------------------- ------------------------ ,yellow ,lemon ,yellow #b #aj ---- #fi #a ---- #d #aa ---- #fi #a ---- #f #ad ---- #fi #a ---- #h #af ---- #gj ---- ---- #aj #bj ---- #gj ---- ---- #ab #bb ---- #gj ---- ---- ,open #bf ---- #gj ---- ---- ---------------------------------------- ------------------------ ,blue4 ,violet4 ,cobalt ,blue #b #aj ---- #aae ---- ---- #d #aa ---- #aae ---- ---- ,green4 #f #ad ---- #ajg #b ---- ,violet4 #h #af ---- #aje #e ---- #aj #bj ---- #aje #e ---- #ab #bb ---- #aje #e ---- ,open #bf ---- #aje #e ---- ---------------------------------------- ------------------------ ,red4 ,orange4 ,light4 ,chrome ,orange #b #aj ---- #cd #fj ---- #d #aa ---- #cd #fj ---- #f #ad ---- #cj #fb ---- #h #af ---- #cj #fj #je #aj #bj ---- #cb #fj #je #ab #bb ---- #cb #fj #je ,open #bf ---- #cb #fj ---- ---------------------------------------- ------------------------ ,yellow4 ,green4 ,emerald ,green #b #aj ---- #b #fd #je #d #aa ---- ---- #fd #je #f #ad ---- ---- #fd #je #h #af ---- ---- #ff #bj #aj #bj ---- ---- #ff #bj #ab #bb ---- ---- #ff #bj ,open #bf ---- ---- #ff #je ---------------------------------------- ------------------------ ,red4 ,violet4 ,mauve #b #aj ---- #cj #gd ---- #d #aa ---- #cj #gd ---- #f #ad ---- #cj #gb ---- #h #af ---- #bh #gb ---- #aj #bj ---- #bh #gb ---- #ab #bb ---- #bh #gb ---- ,open #bf ---- #bh #gb ---- ---------------------------------------- ------------------------ ,,table ,v4 ,,coloured ,,surfaces ,table of ,varying ,luminous ,intensities ---------------------------------------- ----------------- ,red4 ,yellow4 ,blue4 ---------------------------------------- ---- ,inches ,light 8,carmine40 8,lemon40 8,cobalt40 ,square4,units4 --------------------------------------- ,r4 ,or4 ,blk4 ,y4 ,or4 ,b4 ,vi4 ,blk4 ---------------------------------------- ------------ #b #aj #bjb #c #e #fi #a #aae ---- ---- #d #ad #aia #d #e #fi #a #aae ---- ---- #f #ad #ahie #ei #df #fi #a #ajg #b #a #h #af #afi #aa ---- #gj ----#aje #e ---- #aj #bj #afi #aa ---- #gj ----#aje #e ---- #ab #bb #afi #aa ---- #gj ----#aje #e ---- ,open #bd #bf #afi #aa ---- #gj ----#aje #e ---- ---------------------------------------- ----------------- ---------------------------------------- ----------------- ,orange4 ,green4 ,violet4 ---------------------------------------- ---- ,inches ,light 8,chrome40 8,emerald40 8,fr4 ,mauve40 ,square4,units4 --------------------------------------- ,or4 ,r4 ,light4 ,gr4 ,y4 ,light4 ,vi4 ,r4 ---------------------------------------- ------------ #b #aj #f #cd #je #fd #b #je #gd #c #d #ad #f #cd #je #fd #b #je #gd #c #f #ad #fb #c #je #fd---- #je #gb #c #h #af #f #c ---- #ff---- #b #gb #bh #aj #bj #f #cb ---- #ff---- #b #gb #bh #ab #bb #f #cb ---- #ff---- #b #gb #bh ,open #bd #bf #f #cb ---- #ff---- #je #gb #bh ---------------------------------------- ----------------- ,,chapter ,,xii4 ,the ,physiological ,light ,unit4 ,,diffused ,,light4 ,the physiological values of light intensities determined by the absorptive method1 differ in some respects1 from the intensities based on the inverse ratio of the squares of distance between the shadows of two lights4 ,however valuable this method of calculating light intensities may be from a mathematical point of view1 it does not express the physiological appreciation of light differences4 ,the dimensions of the light unit used in the following experiments have already been described4 ,this method cannot deal exhaustively with intense direct lights1 on account of the presence 7activity7 of the disturbing red ray which prevents total absorption4 ,such lights must first be modified by intercepting media of known diffusive value1 or by reflection from a white surface4 ,one object of these experiments was to obtain more insight into the physiological conditions of light1 as bearing on the question of standardization4 ,the first two experiments are records of intensity changes by time1 in ,morning and ,evening light1 and are of interest1 as bearing on the lowest luminosities for reading1 for viewing objects at different distances1 and for defining the limits at which colours visually disappear4 ,the measurements are marked in neutral tint units and plotted in curves in ,charts #a and #b4 ,the numbers on the single curve in the ,morning chart represent total absorption of the direct light #bj degrees above the horizon4 ,the upper curve in the ,evening chart also represents the direct light1 whilst the under curve represents the light values as reflected from a lime sulphate surface2 except in the case of the reading notes when it represents the printed paper surface4 ,the difference between the two curves is the loss of light incident on reflection1 but this must not be rigidly interpreted for all cases1 as there is reason for supposing it varies with different lights4 ,,direct ,,lights4 ,in measuring the physiological intensity of direct lights1 the presence 7activity7 of the unabsorbable red ray1 prevents their being dealt with directly by the absorptive method4 ,such lights can1 however1 be made measurable by a sufficient diffusion1 as already explained in the case of direct sunlight1 the proportion of diffusion required1 being more or less according to the intensity of the light2 in the following examples1 one reflection from a white surface or from the ordinary grease spot arrangement1 was found to be sufficient4 ,note4--,light reflected from grease is not above suspicion1 it being governed by the law of specific absorption already dealt with4 ,illustration3 ,chart #a4 ,evening ,light ,march #ahth4 #aijf4 ,upper ,curve #bj above ,horizon ,lower ,curve as ,reflected from a #a ,foot ,square ,lime ,sulphate ,screen ,illustration3 ,chart #b4 ,morning ,light ,decr4 #agth4 #aijg4 #bj above ,horizon ,illustration3 ,chart #c4 ,luminous ,intensities of #a1 #b #c ,standard ,candles4 ,illustration3 ,chart #d4 ,luminosity of ,gas from ,burner ,reduced to ,equal #a1 #b #c ,candles at #a ,foot4 ,illustration3 ,chart #e4 ,luminosities of ,paraffin ,lamp ,reduced to #a1 #b #c ,candles at #a ,foot4 ,the experiments were carried out on a home-made twelve-foot photometer1 with the usual protected lantern at each end1 one being removed for present purposes4 ,the grease spot carrier was replaced by a one-foot square diaphragm1 with a standard white surface2 this travelled the whole length of the photometer at right angles to the light1 and the readings made at one-foot intervals at an angle of #de degrees1 #aj inches distance from the white surface4 ,charts #c1 #d and #e deal with experiments1 with one1 two and three standard candles of the ,london ,gas ,referees4 ,the curves represent the physiological rate of declining luminosities by distance4 ,some characteristic differences from other lights are brought together in ,charts #d and #e4 ,the slight irregularities in the curves are probably due to the readings being made at half unit intervals4 ,these acting sometimes in opposite directions1 fully account for want of symmetry in the curves4 ,a noticeable feature in these experiments is the small amount of physiological luminosity added by each successive candle to the first4 ,theoretically1 if one candle equals #ba units intensity1 two should equal #db1 and three #fc1 whereas the physiological additions of luminosity are not only much less1 but vary with different luminous intensities1 as will be seen by the following comparisons3-- #a #b #c ,candle ,candles ,candles ,total4 ,theoretical #ba #ba #ba #fc ,physiological #ba #c #f #cj ,chart #d represents the ,luminosity of gas from a batswing burner reduced to one1 two and three candle power at one foot distance4 #a #b #c ,candle ,candles ,candles ,total4 ,theoretical #ba #ba #ba #fc ,physiological #ba #c #g #ca ,chart #e represents the ,luminosity of a hand ,paraffin ,lamp similarly reduced4 #a #b #c ,candle ,candles ,candles ,total4 ,theoretical #ba #ba #ba #fc ,physiological #ba #c #f #cj ,,photographic ,,energies ,,of ,,different ,,rays ,the following experiments are preliminary only1 and were undertaken to determine the relationship of the several colours of the tintometrical scales1 to their associated photographic values1 under different conditions of light and times of exposure1 the end in view being the hope of standardizing screens1 papers and impressions4 ,the standardized colours act as selective light absorbents on the same principle as screens for trichromatic colour work1 but differ from these in their having a definite standard of colour depth and colour purity4 ,work of this character requires paper of a known degree of sensitiveness1 but on inquiry it was found that no reliable standard had as yet been established4 ,on this1 six makes of 8white0 paper were purchased in the open market and submitted to exposures under the following conditions3-- ,six slips of the sensitized papers were covered by a thin metal plate1 pierced by six rows of apertures1 a complete row lying over each sample of paper4 ,the rows contained seven apertures each1 one being left uncovered to receive the full energy of the impinging light4 ,the remaining six were covered respectively by a ,red1 ,orange1 ,yellow1 ,green1 ,blue or ,violet standardized screen of #ae units colour intensity2 the whole was fitted into a suitable exposure frame4 ,many exposures were made1 from which the four following were selected3-- ,no4 #a4 #bj min4 exposure to a dull sky4 #b4 #aj bright sunlight4 #c4 #bj #d4 #cj ,the results are arranged in ,tables ,,vi and ,,vii4 ,table ,,vii contains results of different exposures under sunlight conditions4 ,,table ,,vi4 ,,dull ,,south ,,light4 #bj ,minutes' ,exposure on ,white ,sensitized ,papers4 ---------------------------------------- ----------------- ,pap- ers ,,open ,,screen4 ,,red ,,screen4 ,,orange ,,screen4 ---------------------------------------- ----------------- ,blk4 ,or4 ,red4 ,blk4 ,or4 ,yel4 ,blk4 ,or4 ,red4 #a #gh #db #fj #bj #dh #cj ---- #c #b ,red4 #b #fj #ej #ee #ai #ca #d ---- ---- ---- ,yel4 #c #gh #cb #gj #bg #dg #cj ---- ---- ---- ,red4 #d #gb #dc #fj #bb #cb #b ---- ---- ---- #e #eh #gb #dj #ai #bc #h ---- ---- ---- #f #ef #gd #dj #ah #bf #f ---- ---- ---- ---------------------------------------- ----------------- ---------------------------------------- ---------------------------------- ,pap- ers ,,yellow ,,screen4 ,,green ,,screen4 ,,blue ,,screen4 ,,violet ,,screen4 ---------------------------------------- ---------------------------------- ,blk4 ,or4 ,red4 ,blk4 ,or4 ,red4 ,blk4 ,or4 ,red4 ,blk4 ,or4 ,red4 #a #bj #cj #af ---- ---- ---- #ci #gf #ce #b #d #aj ,yel4 #b #d #d #aj ---- ---- ---- #dc #ib #de #b #h #h ,red4 #c #ab #e #h ---- ---- ---- #cg #ic #bj #g #f #i ,yel4 #d #ab #a #ab ---- ---- ---- #cd #aa #aj #g #g #i #e #aj #c #c ---- ---- ---- #cc #hg #bj #c #c #ab ,red4 #f #b #c #d ---- ---- ---- #cf #hi #ae #d #b #i ---------------------------------------- ---------------------------------- ,,table ,,vii4 ,,bright ,,sunlight 7,south71 #ah--i--ab4 #aj ,minutes' ,exposure on ,white ,sensitized ,papers4 -------------------- ------------------------------------- ,,no4 ,,open ,,screen4 ,,red ,,screen4 ,,orange ,,screen4,,yellow ,,screen4 ---------------------------------------- ------------------ ,blk4 ,or4 ,red4,blk4 ,or4 ,yel4,blk4 ,or4 ,red4,blk4 ,or4 ,red4 #a #hd #af #febh #fh #ai #cd #ada #ee #bc #ga -- #b #hb #bj #fcbg #dg #cf-- -- -- #h #ai #gj #c #gh #bb #gebd #gj #da-- -- -- #bd #db #hj #d #gh #af #hfbd #ed #cb-- -- -- #ae #bc #gj #e #fd #dd #ggbd #eb #cj-- -- -- #i #ah #hj #f #eb #fc #eebc #ea #cj-- -- -- #aa #bj #hj ,,bright ,,sunlight 7,south71 #ah--i--ab4 #bj ,minutes4 ,vio4 ,red4 ,or4 ,red4 ,or4 ,yel4 ,red4 #a #ajf #ad #ejgj #bb #hcaa #cf #i #ajj -- #gj ,red4 ,or4 #b #ajj -- #hgj #bf #gd-- #aj #c #gd #bj #cf ,or4 #c #ib #af #bbde #ee #hjah #gd -- #eb #db #ha ,or4 #d #ajf #d #cefj #db #hc #dd #acf #h #ij #be #ej #e #ajj #h #egfb #dj #hc-- #g #de #gj #ej #dj #f #fb #df #ggej #ge #dj #b #d #e #ed #ga #de ,,bright ,,sunlight 7,south71 #ah--i--ab4 #cj ,minutes4 ,or4 ,red4 ,or4 ,red4 ,or4 ,red4 ,or4 ,red4 #a #ajf #i #aefd #dd #egbf #gh #aa #eb #cd #ajd #b #ib #ad #bifb #ec #ee #a #g #d #gh #cj #eb #c #ajh #ab #aegb #cd #hd #g #bj #b #ib #af #eb #d #ajj #bj #aefb #dd #fi #e #aj #g #hb #bj #gc #e #if #dd #deeh #ej #gb #b #ai #g #fb #ch #fe #f #ff #gi #ejdh #gb #ej #b #e #ee #ej #ge #bj ---------------------------------------- ------------------ ,,bright ,,sunlight 7,south71 #ah--i--ab4 #aj ,minutes' ,exposure on ,white ,sensitized ,papers4 ---------------------------------------- ---- ,,no4,,green ,,screen4 ,,blue ,,screen4,,violet ,,screen4 ---------------------------------------- ---- ,blk4 ,or4 ,red4,blk4 ,or4 ,red4,blk4 ,or4 ,yel4 #a #bf #fi #ajeb #dd #hd #age #cfe #dj #b -- #ae #jcfj #ch #fg #ag #ci #dj #c #bb #jb #jdef #ei #fe #ae #ce #ab #d #ai #je #abdh #ef #ff #ac #cb -- ,red4 #e -- -- -- #dj #aje #bj #f #ag #aj #f -- -- -- #dj #aae #aj #e #ai #aa ,,bright ,,sunlight 7,south71 #ah--i--ab4 #bj ,minutes4 ,or4 ,yel4 ,or4 ,red4 ,or4 ,red4 #a #ca #fa #ah #hj #bj #he #de #ge #de ,or4 #b #ai #cg #h #hh #f #cf #ej #fe #de #c #aj #gj #af #hf #ad #ce #dj #he #de #d #ah #dh #ab #hj #bb #fh #de #ge #de #e #ag #di #ad #gf #bd #hj #dj #he #dj ,red4 #f #ah #cd #d #fd #dd #hb #ce #he #aj ,,bright ,,sunlight 7,south71 #ah--i--ab4 #cj ,minutes4 ,or4 ,yel4 ,or4 ,red4 ,or4 ,red4 #a #aj #fh #b #fd #bf #ge #db #fh #fj #b #ah #cd #b #hd #h #ch #ed #ha #aj #c #bb #eb #bb #hj #bj #ge #de #he #dj #d #be #dg #bj #hj #af #gd #cg #ajc #aj ,yel4 #e #af #db #bh #gf #bf #fh #ca #id #ae #f #ae #ci #b #fd #gf #ee #cd #ig #ae ---------------------------------------- ---- ,it would be unsafe to draw definite conclusions from a few experiments1 but so far as permissible1 the results show considerable differences1 both in depth and in colour1 of the energy of the different rays1 for instance-- ,compare ,nos4 #a and #f under #bj min4 sunlight4 ,black4 ,orange4 ,red4 ,no4 #a #ajf #ad #ej ,no4 #f #fb #df #gg or again #c and #f1 the maximum and minimum1 under #cj min4 exposure4 ,black4 ,orange4 ,red4 ,no4 #c #ajh #ab #ae ,no4 #f #ff #gi #ej ,the sensitiveness of ,nos4 #b1 #d and #e appears to have been exhausted by #bj min4 exposure to sunlight1 further exposure showing no reaction2 whilst the sensitiveness of ,nos4 #a1 #c and #f do not appear to have been exhausted by #cj min4 sunlight exposure4 ,other noticeable points are the small action under the ,orange1 ,green and ,violet screens1 and the greater1 although variable proportion of colour to black under all the colour screens4 ,,trichromatic ,,colour ,,screens4 ,table ,,viii contains the colour measurements of five sets of screens for trichromatic colour work which have come from time to time under the writer's notice4 ,the measurements are the tintometrical colour units required to match the screens under daylight conditions1 and are classified under the theoretically accepted terms of ,red1 ,green and ,violet4 ,,table ,,viii4 ---------------------------------------- ---------------------------------- ,set4 ,,red ,,screens4 ,,green ,,screens4 ,,violet ,,screens4 ---------------------------------------- ---------------------------------- ,no4 ,red4 ,or4 ,vi4 ,light4 ,yel4 ,green4 ,or4 ,light4 ,blue4 ,green4 ,black4 #a #aaij ---- ---- #af #bgj #cfj ---- #ij #cbj #ad #ff #b #bdb #h ---- ---- #hi ---- #a ---- #acj ---- #ca #c #bfd ---- #h ---- #ge ---- #ad ---- #aff ---- #cb #d #bbf ---- ---- ---- #gf ---- #ad ---- #aec ---- #ca #e #baj ---- #ij ---- #bhj #adj ---- ---- #bhj ---- #bh ---------------------------------------- ------------------------------------ ,the ,red screens are all practically pure except ,no4 #e1 which transmits also #cj per cent4 ,violet4 ,no4 #a is distinguished by its greater colour depth and purity1 the degree of which latter is recorded at #af light units brighter than standard4 ,in the ,green division1 only ,nos4 #a and #e transmit any green1 ,no4 #a transmitting also #dbh per cent4 yellow and being #ij units brighter than standards2 ,no4 #d transmits #fff per cent4 yellow to #ccc per cent4 green2 ,nos4 #b1 #c and #d are all yellows tinged with orange4 ,in the ,violet division1 ,nos4 #b1 #c1 #d and #e are all pure blues2 ,no4 #a is tinged with green4 ,appendix ,i ,,colour ,,education ,the time has passed when it might have been considered necessary to preface a handbook on the teaching of colour by arguments to prove that it is a legitimate subject of instruction in schools1 but it has not hitherto been sufficiently recognized that the early stages of such instruction must be on sound lines and that nothing must be taught which will afterwards have to be unlearned4 ,apart from the pleasure its sensations give to all properly constituted persons1 the study of colour has an intellectual value in common with other branches of science4 ,it strengthens the judgment by constantly requiring thought and precision in definition1 it also develops the faculty of colour perception even to the point of curing some forms of colour blindness4 ,in addition to this1 it forms a necessary part of the instruction in all schools in which drawing is properly taught by methods which demand from the pupils faithful representations of the appearances of actual objects in colour as they are seen4 ,in the past the systematic study of colour has been more or less neglected from two principal causes3 first1 the want of a comprehensive scheme of colour nomenclature capable of describing all colours in terms precise enough for general understanding and record2 and1 second1 the absence of any reliable means of reproducing any specific colour if lost or faded4 ,both these conditions may now be secured by the use of the standardized coloured glasses supplied with the ,colour ,educator1 and this work is intended to bring the subject before teachers in such a way as to make each point perfectly easy of demonstration to a class in a systematic manner4 ,to-day the value and importance of a keen perception of colour and of an apparatus furnishing definite colour standards1 though perhaps not much appreciated by the general public1 are widely recognized in the industrial and scientific world2 and it is evident that in these days of keen commercial competition between nations we cannot afford to neglect any means which will enable us to maintain present industries and to develop new ones4 ,general ,remarks4--,it is not advisable to introduce colour theories to pupils before they know the names of the different colours1 but1 as the glasses used in the apparatus are graded for colour-depth according to a set of scales now generally accepted as of standard value1 a short description of the derivation of the colour names will be of service when the pupils are sufficiently advanced4 ,the names of the six spectrum colours1 ,red1 ,orange1 ,yellow1 ,green1 ,blue1 and ,violet1 are accepted by common consent as describing the principal hues into which a beam of white light can be resolved by a diffraction grating or by prismatic refraction4 ,they are also the colours distinguishable in objects of everyday life1 and the following ,educational ,method is based on the fact that they can be separated at will from ordinary daylight4 ,therefore the first educational step is to associate these six colour rays with their respective names1 the pupils being made to understand that there are many degrees of depth in each colour4 ,the ,applications of ,colour to the ,work of ,everyday ,life are so universal that a complete list is almost impossible1 though some of the most important are mentioned below4 ,in a general way the visual characteristics of every visible object are determined by contrasts of light and colour1 outline itself being governed by differences of light intensity4 ,in ,nature1 colour is practically universal4 ,there are few objects perfectly white4 ,most of them have colour of greater or less complexity2 even snow under a cloudless sky has a blue tint which is measurable against such white objects as pure lime sulphate1 zinc white1 etc41 the blue tint being manifestly reflected from the cloudless sky1 as it disappears under a cloudy overcast4 ,some of the ,scientific ,applications of ,colour4--,it associates colour sensations with definite names and values2 discovers and classifies cases of colour-blindness1 and is a preparation for the physical study of light4 ,it is also essential for studying the physiological structure of the organs of vision1 for disclosing abnormal conditions of the blood1 and for measuring the colour of the hair and skin for the anthropological classification of races4 ,it is used in general laboratory work for analytical and original investigation2 and it furnishes standards of value for the petroleum industry1 the ,international ,tanning ,association1 the inter-,states ,cotton ,seed ,oil ,association1 etc4 ,it is also one of the principal factors in all artistic industries2 for1 besides having an important educational value in questions of harmony1 contrast1 and taste1 it is of direct commercial value in such industries as dyeing1 calico printing1 all woollen industries1 wall-paper printing1 paint making1 house decoration1 etc4 ,general ,instructions for ,using the ,apparatus4--,the apparatus consists of a frame having six little windows1 fitted with sliding shutters1 and a tray containing eighteen standardized glasses4 ,the frame must be placed on a table or stand facing the children1 with a window or some other source of diffused white light behind it4 ,care must be taken not to have a coloured background of any kind4 ,the glasses are in three colours1 ,red1 ,yellow1 and ,blue1 of different depths4 ,the depth of colour is marked in figures on each glass1 and corresponding numbers in the three colours are of equal intensity4 ,it is of importance that the six spectrum colour terms should be the only ones used in the preliminary stages4 ,the first step in colour teaching must be to develop and train the perceptive faculties of the children so as to enable them to express in words the colour sensations which are excited4 ,for this purpose it is necessary to begin by demonstrating that the six spectrum colours ,red1 ,orange1 ,yellow1 ,green1 ,blue1 and ,violet1 are derived from white light4 ,red1 ,yellow1 and ,blue should first be dealt with1 and for practical work each pupil should be supplied with three water-colour pigments closely corresponding in hue to the standardized glasses1 viz41 ,crimson ,lake1 ,lemon ,yellow1 and ,cobalt ,blue2 also with a piece of white paper ruled into six small rectangular spaces corresponding to the little windows of the apparatus4 ,as each colour is demonstrated by means of the glass in the apparatus1 each pupil should paint the corresponding pigment in its proper place on the paper4 ,the little shutters being placed in all the six little windows1 remove the top left-hand shutter and insert a deep ,red glass1 thus showing ,red4--,the pupils will name this and then paint the corresponding colour on their papers4 ,next1 remove the shutter below the first one1 and insert a ,yellow glass of the same numerical value as the ,red one1 thus showing ,yellow4--,the pupils will name this and then paint the corresponding colour on their papers4 ,now remove the shutter next below and insert a ,blue glass of the same numerical value as the ,red and ,yellow ones1 thus showing ,blue4--,the pupils will name this and then paint the corresponding colour on their papers4 ---------------- #a ,,red ---------------- #b ,,yellow ---------------- #c ,,blue ---------------- ,there are now exposed to view the three colours which are by artists commonly called primaries1 but it will be found convenient to term ,red1 ,yellow1 and ,blue the ,dominant colours of this system4 ,the second step is to show how the three secondary or subordinate colours are derived or developed4 ,remove the top right-hand shutter and insert a deep ,red and a deep ,yellow glass of equal depth1 showing the pupils that these two colours combined in equal proportions develop ,orange4--,the pupils will name this1 and will then mix their ,red and ,yellow pigments to obtain a similar ,orange which will be painted in its proper place on their papers4 ,now remove the shutter next below and insert a deep ,yellow and a deep ,blue glass of equal depth1 showing the pupils that these two colours combined in equal proportions develop ,green4--,the pupils will name this1 and will then mix their ,blue and ,yellow pigments to obtain a similar ,green which will be painted in its proper place on their papers4 -------------------- #a #d ,,red ,,orange -------------------- #b #e ,,yellow ,,green -------------------- #c #f ,,blue ,,violet -------------------- ,remove the last right-hand shutter and insert a deep ,red and a deep ,blue glass of equal depth1 showing that these two colours combined in equal proportions develop ,violet4--,the pupils will name this1 and mix their ,blue and ,red pigments to obtain a similar ,violet1 which will also be painted in its proper place on their papers4 ,now are exposed to view on the left-hand side the three primary or dominant colours1 and on the right-hand side the three secondary or subordinate colours1 and the whole frame is filled with the six spectrum colours in equal colour depth4 ,corresponding to the colours in the frame1 each pupil's paper should show a similar arrangement of colours1 and the pupils can be taught their spectrum order by reading them in rows horizontally--,red1 ,orange1 ,yellow1 ,green1 ,blue1 and ,violet4 ,the teacher should now take out the coloured glasses and replace the shutters1 except the two top windows1 one of which is left open to show white light1 and the other filled with three equally deep glasses in ,red1 ,yellow1 and ,blue1 showing either black or neutral grey1 and demonstrating the total or partial absorption of light according to their higher or lower numerical unit value4 ,it is of the utmost importance to bear in mind that the glasses are graded for diffused daylight1 and that all artificial lights are more or less coloured and would give a different effect4 ,the same remark applies to light taken direct from coloured objects4 ,in this set the six windows are in one horizontal line1 and should be uncovered in the following order3 ,no4 #a ,window for ,red4 ,dominants #c ,yellow4 #e ,blue4 #b ,orange4 ,subordinates #d ,green4 #f ,violet4 ,one advantage in this method is that when all the colours are in they are arranged in their spectrum order4 ,complex ,colours4--,we have demonstrated that single standard glasses develop the three ,dominant colours1 ,red1 ,yellow1 and ,blue1 and that pairs of equal standard glasses develop the three ,subordinate colours1 ,orange1 ,green1 and ,violet4 ,in order to produce complex colours two standard glasses of unequal value must be used4 ,the degree of inequality does not alter the spectroscopic names of complex colours1 variation in proportions being only a statement of degree4 ,complex ,name4 ,high value4 ,lower4 ,to develop a ,red-,orange insert a ,red and ,yellow4 ,yellow-,orange ,yellow and ,red4 ,yellow-,green ,yellow and ,blue4 ,blue-,green ,blue and ,yellow4 ,blue-,violet ,blue and ,red4 ,red-,violet ,red and ,blue4 ,a reference to the circles1 #g1 #h1 and #i1 on the cards supplied with the apparatus will show that all complex colours are members of the same triad group1 and experiments have shown that the six combinations above are the only ones distinguishable in ,nature1 subject1 however1 to unlimited variations in brightness or dullness4 ,it remains to be shown how these variations are effected4 ,variations in brightness are produced by inserting with the two glasses forming a complex colour the third spectrum colour1 always bearing in mind that it must be less in value than either of the other two4 ,the addition of the third colour has a dulling or saddening effect1 the degree of which is determined by the numerical value of the third colour4 ,the colour produced by the addition of the third colour may be termed a saddened or dingy colour1 the appearance being that of a brighter colour seen in shadow4 ,reviewing the foregoing1 it is demonstrated that primary or dominant colours are transmitted by a single coloured standard glass2 the secondary or subordinate colours are transmitted by two equal standard glasses of different colours2 the complex colours by two unequal standard glasses of different colours4 ,saddened pure colours are developed either by one coloured standard glass combined with two equal standard glasses of different colours and lesser value or by two equal standard glasses of different colours and a third of lesser value4 ,saddened complex colours by three unequal standard glasses of different colours4 ,greys1 which are steps towards blackness1 are produced by three equal standard glasses of different colours4 ,it is well known that ,colour ,blindness is a defect in the vision often involving the confusion of such utterly distinct colour sensations as ,red and ,green1 ,orange and ,violet1 and many others as widely different4 ,in the cases of ,red and ,green the confusions are specially disastrous should the subject be a railwayman or a sailor4 ,it is not1 however1 so well known that many cases of so-called ,colour ,blindness are in reality cases of ,colour ,ignorance1 and the capacity for distinguishing between colours and shades is often latent1 and only waiting to be developed by ,education4 ,when a child persistently misnames colours after having received an amount of instruction sufficient to remove colour ignorance in a normal case1 the errors are probably due to some form of colour blindness4 ,such cases should be registered for further examination1 taking note of the miscalled colours4 ,it would be an additional precaution to change the position of the colours in the windows of the apparatus1 in order to prevent the association of colours with their positions as first given in the instructions4 ,note4--,the paints which most nearly correspond to the colour standards in the ,colour ,educator are tabulated below1 the third column containing their measured colour proportions when they are washed thickly on white paper 7,whatman's74 ---------------------------------------- ------------------------------------ ,colour ,composition in ,standard ,units4 ,spectrum ,artists' ---------------------------------------- -- ,names ,names4 ,red4 ,orange4,yellow4 ,green4 ,blue4 ,violet4 ---------------------------------------- ------------------------------- ,dominants3 ,red ,crimson ,lake #ahj #jd ---- ---- ---- ---- ,yellow ,lemon ,yellow ---- ---- #ff ---- ---- ---- ,blue ,cobalt ---- ---- ---- ---- #ij ---- ,subordinates3 ,orange ,chrome ,orange ---- #gb #af ---- ---- ---- ,green ,emerald ,green ---- ---- #jdj #ed ---- ---- ,violet ,mauve #cc ---- ---- ---- ---- #hb ---------------------------------------- ------------------------------- ,in mixing two dominant colours 7artists' primaries7 to develop subordinates 7artists' secondaries71 their relative colour depth must be taken into account2 for instance1 ,crimson ,lake has a natural colour depth nearly three times that of ,lemon ,yellow2 therefore1 in order to develop a normal ,orange nearly three times the quantity of ,yellow must be used1 presuming that they were originally ground to an equal degree of fineness4 ,it is desirable that a record of the children's own painting should be preserved1 with a view to discriminating between errors arising from ,colour ,blindness and ,colour ,ignorance1 the former perpetuating itself1 and the latter naturally remedying itself4 ,for this purpose painting books containing sets of diagrams corresponding to the figures in the foregoing pamphlet can be supplied4 ,appendix ,,ii ,,the ,,possibilities ,,of ,a ,,standard ,,light ,,and ,,colour ,,unit4#e #e ,reprinted from the ,journal of the ,society of ,dyers and ,colourists1 ,march1 #aiac4 ,no4 #c1 vol4 xxix4 ,the past attempts to standardize light and colour are mainly limited to those radiant energies which excite light and colour sensations under diffused daylight conditions1 because in direct sunlight1 and in most artificial lights1 there are other colour energies1 which1 unless sufficiently modified by diffusion1 disturb the colour readings4 ,there are also latent colour energies1 which only become distinguishable by special means4 ,they do not1 however1 appear to influence diffused daylight colour work4 ,the definition of a normal vision is one which agrees with a majority of others4 ,this definition has proved satisfactory up to the present1 as the normals are many and the colour blind few4 ,light ,intensities4--,there are two methods of determining light intensities by means of a graded scale of light absorbents4 ,first4 ,by total absorption of the light1 when the intensity is directly represented by the unit value of the absorbents required4 ,this method is applicable for low lights1 internal surfaces1 such as a desk1 etc41 where a standard light is not available for comparison4 ,second4 ,by the reduction of a standard light by absorption until it equals the light of the object4 ,in this case the standard must be originally brighter than the object4 ,constants4--,the first requirement in establishing a scale of light and colour units is a means of co-relating visual sensations to a scale of physical colour constants1 in order to secure a power of record and recovery4 ,there is no natural scale available for quantitative colour work1 but artificial scales can be constructed1 and made constants by co-relation at different points with physical colour constants1 and by cross-checking the intervals between these4 ,the scales used in the 8tintometer0 consist of red1 yellow and blue glass1 so graded in equivalents that combinations of equal units transmit colourless light4 ,full details of these have already been placed before the ,society 7see this ,jour41 #ahhg1 p4 #ahf1 and #aijh1 p4 #cf74 ,scale of ,luminous ,intensities4 ,the ,light ,unit4--,the natural terminals in a scale of luminous intensities are black and white1 and the first question which arises is what is black1 and what is white8 as when used in a popular sense each term covers a wide range of differences4 ,in the author's sense the term black means total absence of light1 and the term white means a diffused daylight of given intensity1 as reflected from a lime sulphate surface4 ,in this sense black and white are the terminals of a scale of light intensities2 the scale is divided into units and fractions of units4 ,the unit itself is physiological1 and is not in progressive accord with the mathematical light unit based on the inverse squares of distance4 ,the ,black ,unit4--,ideal black is practically obtained under daylight conditions by viewing a hole in a box with blackened interior1 so arranged that no entering light can be reflected back to the vision4 ,the box used for this purpose is illustrated in ,fig4 #c1 and has one surface covered with standard white for the purpose of easy comparison with the pigments4 ,the standard black aperture 7#a7 is in the middle4 ,the pigmentary blacks 7#b to #aj7 are arranged over this1 and the pigmentary whites and greys 7#aa to #bj7 underneath1 each being numbered in accord with its intensity as tabulated4 ,illustration3 ,fig4 #c4 ,the degrees of blackness are the number of absorptive units required to reduce the standard white to equal the pigments in each case4 ,light ,absorbed by ,various ,pigments4 ---------------------------------------- --------- ,no4 ,absorbed,unabsorbed,initial ,light4 ,light4 ,light4 ---------------------------------------- --------- #a ,black ,hole in ,box #cf -- #cf #b ,optical ,black #bj #af #cf #c ,lamp ,black #ag #ai #cf #d ,vegetable ,black ,a #ag #ai #cf #e ,b #ad #bb #cf #f ,c #ae #ba #cf #g ,indian ,ink on ,paper #ad #bb #cf #h ,solid #ab #bd #cf #i ,boot ,black #aa #be #cf #aj ,black ,lead #i #bg #cf ---------------------------------------- --------- ,this gives a working scale of colourless light intensities1 the terminals being black and white1 with a range of #cf units4 ,the ,standard ,white4--,white is the natural terminal of the luminous end of the scale1 and it is necessary to select a physical objective white as a constant4 ,pure precipitated lime sulphate has been adopted1 and departures from the light intensity of this are recorded in units of lessened light intensity throughout the scale1 comprising all degrees of colourless whites1 greys1 and blacks4 ,strictly speaking1 white is a qualitative term only1 until the degree of variation from the zero of the scale has been established4 ,the measured variation then takes its position in the scale of luminous intensities according to its numerical unit value4 ,light ,absorbed by ,various ,white and ,grey ,pigments4 ---------------------------------------- - ,no4 ,pigments4 ,absorbed,reflected,initial ,light4 ,light4 ,light4 ---------------------------------------- - #aa ,grey ,paint ,e #fj #cjj #cf #ab ,d #ej #caj #cf #ac ,c #dj #cbj #cf #ad ,b #bj #cdj #cf #ae ,white ,paint ,a #jg #cec #cf #af ,white ,paper ,d #jc #ceg #cf #ag ,c #jb #ceh #cf #ah ,b #jbe #cege #cf #ai ,a #jae #cehe #cf #bj ,chinese ,white #jjjf #ceiid #cf ---------------------------------------- - ,as the scale is differentiated into hundredths of a unit1 there can be #ajj variations of white pigments in a single unit1 each quite easily distinguishable from the others4 ,any definite mixture of black and white finds a position on the diagonal of a chart whose co-ordinates are the black and white scales2 for example1 the #bj measured pigments are charted on ,figs4 #d and #e1 the latter being on an enlarged scale1 as the whites would be too crowded to be noted on ,fig4 #d4 ,illustration3 ,fig4 #d4 ,the merging of white into grey1 and of grey into black is gradual1 having no strict lines of demarcation4 ,an example of this method of determining light intensities is illustrated in ,fig4 #f by the light intensities at which different objects are discernible4 ,the points of most interest are1 that colour is indistinguishable as such in lights below #ae units intensity2 and that ordinary work1 such as reading a newspaper1 requires for comfort a minimum of #bh units4 ,the ,colour ,unit4--,the colour unit is physiological1 and its dimensions are determined by the dimensions of the colourless light from which it is derived4 ,this deduction is based on the experimental fact that colourless light is a mixture of the six colour rays--red1 orange1 yellow1 green1 blue1 and violet--in equal proportion1 as illustrated in ,fig4 #g1 showing that a white light of #bj units light intensity is made up to the six colour rays1 each of #bj units colour intensity4 ,this is demonstrated by the fact that any proportion of any colour can be developed at will by means of the glass standard scales already mentioned2 it follows that the smallest disturbance of equivalence between the composing rays results in the development of colour4 ,illustration3 ,fig4 #e4 ,the above remarks apply to both simple and complex colours1 and the complex colours are always dichromes1 being governed by another physiological fact1 which is3 ,that the vision is unable to simultaneously distinguish more than two colours in the same beam of light4 ,the order of their association is definite1 and may be described by saying that the combined two are always adjacent in their spectrum order1 red and violet being considered adjacent for this purpose4 ,it follows that all complex colours are binaries1 and the only possible combinations are as follows3-- ,red with ,orange4 ,orange ,yellow4 ,yellow ,green4 ,green ,blue4 ,blue ,violet4 ,violet ,red4 ,illustration3 ,fig4 #f4 ,in the author's colour nomenclature1 a monochrome is qualitatively described by a single term1 and a complex colour by a combination of two single terms4 ,for a quantitative description1 it is only necessary to add the measured unit value to each term4 ,when there is excess of brightness1 or a saddening factor1 these also must be quantitatively estimated4 ,the colours developed by means of these scales are governed by the same law of selective absorption which governs the development of natural colours1 any of which can be matched and reproduced by means of their established ray proportions4 ,illustration3 ,fig4 #g4 ,the governing law is simple1 and may be stated by saying that the colour developed is always complementary to the colour absorbed1 not in the generally accepted sense that their mixture necessarily makes white light1 but in the sense that they are opposite in the cycle of daylight colours4 ,the dimensions of the unit are necessarily arbitrary1 it was originally selected as being a convenient depth for distinguishing differences1 the scale was then constructed by equal additions and sub-divisions2 the two essentials of a scientific scale being complied with1 in that the divisions were equal and the unit recoverable4 ,the power of recovery lies in the fact that different parts of the scale are co-related to physical colour constants1 which can be prepared in any laboratory4 ,illustration3 ,,plate ,,viii ,,absorption ,,curves ,,of ,,six ,,dyes4 ,to face page #gf4 ,lovibond1 ,colour ,theories4 ,specific ,colour4--,the relationship of colour increase to intensity increase in substances has hitherto been somewhat obscure4 ,it has been sometimes considered that they were in direct proportion1 but in the absence of a means of recording colour sensations1 no definite results were obtainable4 ,illustration3 ,fig4 #h4 ,sufficient information is now available to warrant the formulation of the following law3 8,that every substance has its own rate of colour development for regularly increasing intensities1 which1 when once established1 becomes a constant for identifying similar substances in future40 ,this is the meaning of specific colour1 and when a series of measurements at regularly increasing densities of a given substance have been made1 the specific colour rate of that substance is established4 ,this can be charted in curves and used as a basis for estimating quantities1 properties1 changes of condition1 differences in value1 detecting adulteration1 etc4 ,applications4--,the author has permission to use the names of several gentlemen who have used the tintometrical scales for various purposes4 ,sir ,arthur ,h4 ,church1 ,f4,r4,s41 has employed the tintometrical standards for the purpose of registering the colours of certain wild flowers4 ,sir ,boverton ,redwood has used the scales and system for petroleum investigations4 ,at his instance the specific colour rate of petroleum was established1 and the several composing colours plotted in curves1 as in ,fig4 #h1 where the ordinates represent the scale of units irrespective of colour1 and the absciss the scale of strata thicknesses4 ,the measurements were made at two-inch intervals1 and the four perpendicular lines are at the colour points selected for valuing the four distinguishing marks1 technically known as 8,water ,white10 8,superfine10 8,prime10 and 8,standard40 ,intermediate qualities find their position in the scale of curves according to their measured colour values4 ,this method of standardizing commercial values has also been adopted by the ,international ,tanners' ,association1 the ,inter-,states ,cotton ,seed ,oil ,association1 and other oil industries4 ,also for scale1 solid fats1 and such substances as can be easily melted and measured by transmitted light4 ,varying ,effects of ,different ,lights4 ,pathological ,applications4--,the law of specific colour development was made use of by ,dr4 ,george ,oliver in determining the degrees of hmoglobin in the blood4 ,the method is fully explained in his ,croonian ,lecture before the ,royal ,college of ,physicians of ,london1 ,july #aa1 #ahif4 ,detection of ,forgeries4--,the system and apparatus is used by ,professor ,a4 ,s4 ,osborne1 ,examiner of ,questioned ,documents1 ,new ,york ,city1 for determining the variety of ink1 the age of the writing1 and the detection of forgeries4 ,a full description of the process will be found in his work entitled ,questioned ,documents1 published by the ,lawyers' ,co-operative ,society1 ,rochester1 ,n4,y4 ,illustration3 ,,plate ,,ix ,,six ,,aniline ,,dyes4 ,,curves ,,illustrating ,,the ,,rate ,,of ,,fading ,,by ,,exposure ,,to ,,light4 ,to face page #gh4 ,lovibond1 ,colour ,theories4 ,the application to chemical analysis is too well known to require enlargement here4 ,illustration3 ,fig4 #i4 ,dyes4--,as an example of the use of the system in the valuation of dyes1 ,fig4 #i illustrates the specific colour curves of four samples of ,methylene ,blue4 ,no4 #a was priced at #es4 #i;d4 and ,no4 #b at #es4 per lb41 ,nos4 #c and #d were not priced1 the solutions were measured in percentages from #jjja to #jjdh in distilled water4 ,to find the cost per unit of colour in the priced samples is only a question of simple arithmetic1 which furnishes data for the valuation of the unpriced samples4 ,the yield in the dye vat may not be in direct relation to the solutions in water1 the establishment of this is a question for the expert1 and presents no apparent difficulty4 ,the use of the scheme in recording the degree of fading of dyes has been previously dealt with in the ,journal 7q4v41 #aijh1 p4 #cf74 ,limitations and ,precautions4--,it has been shown that we have analytical control1 within certain limits1 of light and colour under daylight conditions4 ,the general limits for colourless light range from total darkness to #bh units1 when the unabsorbable red ray comes into evidence4 ,for colour1 the general limits range from #bh to #ah units1 between #ah and #ae all colours become indistinct1 but at varying rates1 below #ae1 colour is not distinguishable4 ,the principal disturbing conditions in making observations are want of colour education and insufficient diffusion4 ,in the case of the latter1 the first evidence is the disturbance of constancy by the penetrating red ray4 ,a partial remedy is to interpose a white diffusion screen1 such as tissue paper4 ,time of ,observation4--,this should not exceed five consecutive seconds1 as the keenness of perception decreases by time1 but varies for different colours4 ,angle of ,incidence4--,sixty degrees is safe for most solids1 but for bright or polished surfaces1 such as varnishes1 polished metals1 etc41 the angle must be lessened as the degree of smoothness increases4 ,for very rough surfaces1 such as loosely woven stuffs1 etc41 care must be taken that the lay of the fibre is uniform4 ,distance from the ,object4--,ten inches has been adopted for general work1 but certain visions require more or less as their focus varies from normal4 ,illustration3 ,,plate ,x ,,comparison ,,curves ,,of ,,healthy ,,and ,,diseased ,,blood4 ,to face page #hj4 ,lovibond1 ,colour ,theories4 ,unabsorbable ,colours4--,in addition to the daylight colours already dealt with1 there are1 in direct lights1 colours which do not obey the laws of absorption governing those of diffused daylight4 ,the work already done on these unabsorbable rays has only been incidental1 where they happened to interfere with the standardization of diffused daylight colours4 ,the sensations excited are red and violet4 ,they blend1 producing red-violet mixtures1 but in unequal proportions1 the red being dominant4 ,the red is developed in intense lights by constant interception of neutral tint absorbents4 ,in the case of a #d-volt incandescent light1 the first absorption simply reduces the light intensity without developing colour2 the light is colourless up to #ad units4 ,at #af units the light begins to assume a reddish hue1 which rapidly becomes a brilliant intense red by further interceptions of neutral tint absorbents4 ,violet is developed by constant absorption by blue standards1 which grows in intensity by successive additions up to about #abj units4 ,beyond this point the brilliancy decreases4 ,preliminary experiments point to this ray as fatal to vegetation1 and presumably also to lower forms of organic life4 ,there remains a factor of considerable importance which has not yet received the attention it deserves1 the physiological changes resulting from environment4 ,this aspect of the question has come under the notice of the author by measuring the vision of experts who excelled in given hues4 ,it was generally found that their vision was sensitive to a small increment of their particular colour in harmonies where it was silent to a normal vision4 ,in seeking an explanation of this phenomenon there are at least three possible lines for working3 ,first4 ,is the vision naturally more sensitive to that particular energy8 ,second4 ,is it by careful education8 ,third4 ,is it an unconscious adaptation to surroundings1 such as other organs undergo under changes of environment8 ,illustration3 ,,plate ,,xi ,,specific ,,colour ,,curves ,,of ,,healthy ,,and ,,diseased ,,human ,,blood ,to face page #hb4 ,lovibond1 ,colour ,theories4 ,appendix ,,iii ,,the ,,application ,,of ,,the ,,natural ,,law ,,of ,,specific ,,colour ,,rate ,,by ,,dr4 ,,dudley ,,corbett ,,to ,,the ,,exact ,,measurement ,,of ,x-,,ray ,,dosage4 ,dr4 ,dudley ,corbett4 ,the gradations in the tint given by the ,sabouraud-,noir pastille when exposed to ,x-rays are so fine1 especially in that region of the colour scale where lies the erythema dose1 that many have felt the want of a more accurate means of reading these tints1 as well as a series of reliable standards for comparison4 ,hitherto the only methods at all generally used have been ,hampson's radiometer and ,bordier's radio-chronometer1 the former in this country1 and the latter on the ,continent4 ,hampson's instrument has two disadvantages3 it can only be used with electric light1 and the standards are made of tinted paper liable to get soiled1 and to vary slightly with the changes in the pigment employed4 ,its advantage is that it may be used as a sliding scale1 thus economising the pastilles4 ,some persons1 however1 have considerable difficulty in reading the tints1 the scale rising only by gradations of #a_/d ,b4 ,in the construction of any such instrument1 the really important point is to obtain a reliable standard for ,tint ,b--i4e41 the normal epilation dose4 ,the tints on the ,sabouraud card itself are not always identical1 some representing a dose which will only just epilate1 others an almost dangerous dose for unfiltered rays4 ,the ,tint ,b1 which is the standard1 allows a margin of error of #bj per cent4 on either side4 ,in other words1 #d_/e ,b will almost always epilate1 while #a-a_/e ,b is nearly the limit of safety4 ,this observation is in accordance with the experience of other workers on this subject4 ,in my instrument ,tint ,b has been obtained by measuring the pastille with ,lovibond's tintometer immediately after exposure to the ,x-rays4 ,the pastille was turned to a tint corresponding to an epilation dose which was known to be safe1 as proved by clinical results4 ,this tint was measured directly both by daylight and by artificial light from an #h-;candle power carbon filament lamp with frosted glass shade4 ,i am indebted to ,mr4 ,dean for suggesting the use of ,lovibond's instrument for this purpose4 ,the methods employed in the experimental work have been described in the ,british ,journal of ,dermatology for ,august1 #aiac4 ,by using a very constant focus tube and averaging a large number of readings and correlating the results with those obtained in clinical practice1 we were able to construct the curves indicating the colour developed by the pastille4 ,in these curves1 shown in ,fig4 #aj1 the ordinates are the ,lovibond colour units1 the abscissa the time during which the current was actually passing4 ,when using an interrupter working at a constant speed1 the actual time was taken1 otherwise the number of current interruptions as measured by a dipper tachymeter was used4 ,as was to be expected1 the daylight and electric light curves were quite different4 ,in each case the standard yellow glasses employed were kept constant throughout the curve1 that for daylight being #ae units1 that for electric light #ac units4 ,when these were combined with blue and red glasses in varying units and fractions of a unit1 they gave a colour range which matched the pastille exactly in the changes it undergoes from the unexposed condition to the #b ,b ,tint4 ,the curves are plotted in accordance with ,mr4 ,lovibond's practice--that is1 not as a direct representation of the standard glasses used1 but as showing the colour sensation received by the eye4 ,illustration3 ,fig4 #aj4 ,first1 as to the daylight curve3 ,in order to match the unexposed pastille we interpose between the pastille and the observer's eye a yellow and a blue glass1 plus a certain amount of neutral tint 7composed of three equal colour units74 ,thus the colour sensation received is a yellow green1 together with a certain amount of white light4 ,as the pastille darkens under irradiation1 both the green and the white light disappear1 until at a point just below the #a_/b ,b dose1 there is no other colour present but yellow4 ,after this red glasses are required--i4e41 the colour sensation is a yellow orange1 which gradually deepens owing to an increase in the proportion of red4 ,the yellow curve thus rises till just below the #a_/b ,b point1 and then falls as the orange increases4 ,next1 as to the electric light curve4 ,the unexposed pastille has but a trace of green1 which is soon lost4 ,the orange begins much earlier than in daylight1 and thus at ,tint ,b has reached a higher point than in daylight4 ,from this point the orange and yellow parts of both curves run practically parallel with one another up to #b ,b4 ,beyond #b ,b the readings become more difficult4 ,i have not determined the point when no more colour develops1 as it has no great practical value1 though it might well be of interest from a physico-chemical standpoint4 ,in my radiometer the standards are composed of the ,lovibond standard glasses in combination4 ,the apparatus itself consists of an optical instrument or viewing box4 ,this is divided by a central partition1 so that on looking through the eyepiece one sees a white background through two small circular apertures4 ,on one side1 level with the background1 is a fitting to take the pastille in its holder4 ,on the other side is a groove in the instrument itself for the insertion of the standard glasses4 ,a similar groove is fitted on the pastille side of the instrument to take neutral tints if required4 ,the colour of the pastille as seen by reflected light can thus be compared with that obtained by transmitted light through the standard glasses seen against the white background4 ,a difference of #a_/e ,b or #a ,h is quite easily perceivable4 ,it is usually of no great importance to obtain extremely accurate measurement of the smaller fractions below #a_/c ,b4 ,where this is necessary1 neutral tints must be used when working with daylight4 ,with electric light these are unnecessary4 ,when required the neutral tints are interposed between the pastille and the eye to absorb the white light reflected from the pastille4 ,the neutral glasses required are #ae for the unexposed pastille1 #jf for #a_/d ,b1 and #jb for #a_/c ,b4 ,these values are subject to slight variations due to changes in the varnish of the pastille emulsion4 ,the difficulty can always be avoided by using electric light1 where a trace of neutral tint is needed only when matching the unexposed pastille--an unimportant point4 ,method of ,use4--,the choice of daylight or artificial light is a personal matter1 but one should practise reading the scale with both4 ,the use of the instrument shows that the pastille fades very nearly as quickly under electric light as it does under daylight4 ,the following precautions should be observed3 ,in daylight work in a good white light1 avoid shadows and yellow light of any kind4 ,with electric light use an #h-;candle power carbon-filament lamp with frosted glass and a suitable white shade so arranged that the pastille is #h inches from the lamp4 ,no other light should be allowed to reach the pastille during examination4 ,a low power metal-filament lamp may be used1 but greater accuracy will be obtained with a carbon-filament lamp which was used for the experimental work4 ,the lamp should be discarded as soon as the light becomes yellow from prolonged use4 ,whether in daylight or electric light1 the examination must be rapid to avoid the fading of the pastille4 ,when it is desired to give an accurate #a ,b dose1 it is better to put up the #d_/e ,b standard first4 ,it is then easy to calculate how much more exposure is required for the extra #a_/e ,b4 ,it is important to adjust the pastille carefully so that none of the unirradiated green portion is visible through the small aperture1 as this will upset the reading4 ,in very accurate dosage new pastilles should be used1 as a bleached pastille never returns exactly to its original tint4 ,when such a bleached pastille is irradiated the colour changes start a little farther down the curve1 and thus the tint for a given dose must be taken a little above the normal tint4 ,this increase is very slight1 but is nevertheless quite appreciable1 and may amount to as much as #e and #aj per cent4 ,even then the margin for error is ample in the neighbourhood of the ,b tint1 and if a pastille is not used more than three times1 and is well bleached in daylight after each exposure1 no serious error is likely to occur4 ,a standard white background should always be used1 and discarded for a new one when it gets dirty4 ,the colour standards usually provided are those in common use--namely1 #a_/d1 #a_/c1 #a_/b1 #d_/e1 #a1 #a'1 and #b ,b1 but it is quite easy to make up standards for any point on the curve4 ,the symbol 8,b10 as the erythema or epilation dose1 has been retained1 as it was thought inadvisable to add to the number of such symbols already existing4 ,to sum up3 #a4 ,the experimental work has determined the exact colour changes occurring in the ,sabouraud pastille when exposed to ,x-rays4 #b4 ,these experiments have established a permanent standard for ,tint ,b1 which matches the pastille exactly1 does not fade1 is easily kept clean4 ,these coloured glasses can be readily and accurately reproduced1 as they are standardized spectroscopically by a firm who specialise in such work4 ,the standard will therefore remain constant so long as the ,sabouraud emulsion remains unaltered4 #c4 ,glasses may be prepared of the correct tint for any fraction or multiple of this dose up to #b ,b or #aj ,h4 #d4 ,either daylight or electric light can be used4 #e4 ,the optical instrument itself1 by cutting off extraneous light1 greatly assists the colour comparisons1 so that the practical error need never exceed #aj per cent4 ,,index ,abnormal light1 #ac ,analysis of white light1 #aa1 #ac ,arbitrary scales1 #i ,artists and scientists1 #a1 #b ,beam of white light1 #g1 #aa ,black units1 #af1 #bc ,black1 ideal1 #ae1 #aa ,blood curves1 #cc ,code of laws1 #g ,colour charts1 #ca1 #ci education1 #ei equivalence1 #aj nomenclature1 #ag1 #ba qualitative1 #ag1 #ai1 #bd quantitative1 #bd scales1 #bj1 #bi standardization1 #bj1 #fi theories1 #b1 #c ,coloured surfaces1 #dd ,colours1 complex1 #ah sadder than standards1 #be simple1 #ag ,corbett1 ,dr4 ,dudley's1 radiometer1 #hc ,daylight colours1 #bd1 #hd measurement1 #ad ,diffused light1 #aj1 #dc ,direct lights1 #df ,dulled colour1 #aj1 #ah-bf1 #cf ,equivalent colour units1 #g1 #i1 #bi ,fog1 whiteness of1 #aj ,glass standards1 #bj ,human blood curves1 #hb ,laws of colour1 #g ,light1 #aa1 #ac1 #db1 #de-df1 #ha-hd abnormal1 #h brighter than standards1 #ad1 #bg direct1 #df for colour work1 #db intensities1 #db1 #dc white1 #ad ,lovibond's new colour theory1 #e ,matching colours brighter than standards1 #ah complex colours1 #ag ,measuring and naming colours1 #ba ,monochromes1 #ag1 #ai ,munro1 ,dr41 #cd ,neutral tint1 #ah1 #bd1 #bf ,north light1 #ae ,past theories1 #c ,photographic energies1 #ec ,physical colour constants1 #h ,pigmentary black1 #ae1 #ga ,primary colours1 #a ,prismatic spectrum colours1 #bi ,qualitative analysis of colour1 #ag1 #ai1 #bd ,quantitative analysis of colour1 #bd ,radiometer1 #hc ,rate of colour absorption1 #h ,rays1 six colour1 #g ,red ray1 #da ,scales1 arbitrary colour1 #i coloured1 #aj1 #bj cross checking of1 #i ,scientists and artists1 #a1 #b ,sea fog1 #aj ,specific colour1 #cb ,spectrum colours1 #d1 #ah1 #cf ,three colours1 #aj1 #eg ,time1 appreciation of colour by1 #db ,ultra violet1 #cb1 #dj ,unit1 checking of1 #i ,unit1 neutral tint1 #ah1 #bd1 #bf ,wave length position1 #cg1 #ch ,white light1 #aa1 #ac ,butler ,tanner ,frome and ,london ,transcriber's notes3 ,in the text version1 italics are represented by underscores1 and bold and black letter text by equals symbols4 ,superscripts are represented by and subscripts by ,missing or incorrect punctuation has been repaired4 ,inconsistent spelling and hyphenation have been left1 ,in the html version1 dittos have been replaced by the repeated text so that text aligns for easier reading4 ,very wide tables 7,v and ,,vi and ,,vii7have been split to fit on portrait oriented pages4 ,the following mistakes have been noted3 p4 #ba4 ,ni,s,o#dg;,h#b,o1 tem4 is formatted inconsistently4 ,left as printed4 p4 #dj4 ,fraunhoper is almost certainly a typo for ,fraunhofer4 ,left as printed4 p4 #df4 interpretated changed to interpreted4 p4 #ee4 ,in ,paper #f of table1 ,red screen1 yellow entry1 from alignment and logic1 the #f should be 4#f4 ,left as printed p4 #fa conditonschanged to conditions4