,a ,,treatise ,,on ,,meteorological ,,instruments4 ,,london3 ,,printed ,,by ,,williams ,,and ,,strahan1 #g ,,lawrence ,,lane1 ,,cheapside1 ,e4,c4 ,a ,,treatise ,,on ,,meteorological ,,instruments3 ,,explanatory ,,of ,,their ,,scientific ,,principles1 ,,method ,,of ,,construction1 ,,and ,,practical ,,utility4 ,,by ,,negretti ,,zambra1 ,,meteorological ,,instrument ,,makers ,,to ,,the ,,queen1 ,,the ,,royal ,,observatory1 ,,greenwich1 ,,the ,,british ,,meteorological ,,society1 ,,the ,,british ,,and ,,foreign ,,governments1 ,,etc4 ,,etc4 ,,etc4 ,,london3 ,,published ,,and ,,sold ,,at ,,negretti ,,zambra',s ,,establishments3 #a ,,hatton ,,garden1 ,e4,c41 #ei ,,cornhill1 ,e4,c41 #abb ,,regent ,,street ,w41 ,,and #aec ,,fleet ,,street1 ,e4,c4 #ahfd4 ,price ,five ,shillings4 ,,preface4 ,the national utilisation of ,meteorology in forewarning of storms1 and the increasing employment of instruments as weather indicators1 render a knowledge of their construction1 principles1 and practical uses necessary to every well-informed person4 ,impressed with the idea that we shall be supplying an existing want1 and aiding materially the cause of ,meteorological ,science1 in giving a plain description of the various instruments now in use1 we have endeavoured1 in the present volume1 to condense such information as is generally required regarding the instruments used in ,meteorology2 the description of many of which could only be found in elaborate scientific works1 and then only briefly touched upon4 ,every ,meteorological ,instrument now in use being fully described1 with adequate directions for using1 the uninitiated will be enabled to select those which seem to them best adapted to their requirements4 ,with accounts of old or obsolete instruments we have avoided troubling the reader2 on the other hand1 we were unwilling to neglect those which1 though of no great practical importance1 are still deserving of notice from their being either novel or ingenious1 or which1 without being strictly scientific1 are in great demand as simple weather-glasses and articles of trade4 ,we trust1 therefore1 that the work 7however imperfect71 bearing in mind the importance of the subject1 will be acceptable to general readers1 as well as to those for whose requirements it has been prepared4 ,the rapid progress made in the introduction of new apparatus of acknowledged superiority has rendered the publication of some description absolutely necessary4 ,the ,report of the ,jurors for ,class ,,xiii4 of the ,international ,exhibition1 #ahfb1 on ,meteorological ,instruments1 fully bears out our assertion1 as shown by the following extract3-- ,the progress in the ,english department has been very great2--in barometers1 thermometers1 anemometers1 and in every class of instruments4 ,at the close of the ,exhibition of #ahea1 there seemed to have arisen a general anxiety among the majority of makers to pay every attention to all the essentials necessary for philosophical instruments1 not only in their old forms1 but also with the view of obtaining other and better forms4 ,this desire has never ceased2 and no better idea can be given of the continued activity in these respects1 than the number of patents taken out for improvements in meteorological instruments in the interval between the recent and preceding exhibitions1 which amount to no less than forty-two4 99 99 99 ,in addition to numerous improvements patented by ,messrs4 ,negretti and ,zambra1 there is another of great importance1 which they did not patent1 viz4 enamelling the tubes of thermometers1 enabling the makers to use finer threads of mercury in the construction of all thermometers2 for the contrast between the opaque mercury and the enamel back of the tubes is so great1 that the finest bore or thread of mercury1 which at one time could not be seen without the greatest difficulty1 is now seen with facility2 and throughout the ,british and ,foreign departments1 the makers have availed themselves of this invention1 the tubes of all being made with enamelled backs4 ,it is to be hoped that the recent exhibition will give a fresh stimulus to the desire of improvement1 and that the same rate of progress will be continued4 ,to fulfil the desire of the ,international ,jury in the latter portion of the above extract will be the constant study of ,,negretti ,,zambra4 #ast ,january1 #ahfd4 ,,table ,,of ,,contents4 ,,chapter ,i4 ,,instruments ,,for ,,ascertaining ,,the ,,atmospheric ,,pressure4 ,,section #a4 ,principle of the ,barometer4 #b4 ,construction of ,barometers4 #c4 ,fortin's ,barometer ,cistern4 #d4 ,,standard ,,barometer4 #e4 ,correction due to ,capillarity4 #f4 ,temperature4 #g4 ,height4 #h4 ,the ,barometer ,vernier4 #i4 ,,self-,,compensating ,,standard ,,barometer4 #aj4 ,,barometer ,,with ,,electrical ,,adjustment4 #aa4 ,,pediment ,,barometers4 #ab4 ,the ,words on the ,scale4 #ac4 ,correction due to ,capacity of ,cistern4 #ad4 ,,public ,,barometers4 #ae4 ,,fishery ,,or ,,sea-,,coast ,,barometers4 #af4 ,admiral ,fitz,roy's ,words for the ,scale4 #ag4 ,instructions for ,sea-coast ,barometer4 #ah4 ,french ,sea-coast ,barometer4 #ai4 ,,common ,,marine ,,barometer4 #bj4 ,,the ,,kew ,,marine ,,barometer4 #ba4 ,method of verifying ,barometers4 #bb4 ,,fitzroy',s ,,marine ,,barometer4 #bc4 ,words for its ,scale4 #bd4 ,trials of this ,barometer under ,gun-fire4 #be4 ,,negretti ,,and ,,zambra',s ,,farmer',s ,,barometer ,,and ,,domestic ,,weather-,,glass4 #bf4 ,rules for ,foretelling the ,weather4 #bg4 ,causes which may bring about a ,fall or a ,rise in the ,barometer4 #bh4 ,use of the ,barometer in the ,management of ,mines4 #bi4 ,use of the ,barometer in estimating the ,height of ,tides4 ,,chapter ,,ii4 ,,syphon ,,tube ,,barometers4 #cj4 ,principle of4 #ca4 ,,dial1 ,,or ,,wheel1 ,,barometers4 #cb4 ,,standard ,,syphon ,,barometer4 ,,chapter ,,iii4 ,,barographs1 ,,or ,,self-,,registering ,,barometers4 ,,section #cc4 ,,milne',s ,,self-,,registering ,,barometer4 #cd4 ,,modification ,,of ,,milne',s ,,barometer4 #ce4 ,,king',s ,,self-,,registering ,,barometer4 #cf4 ,,syphon1 ,,with ,,photographic ,,registration4 ,,chapter ,,iv4 ,,mountain ,,barometers4 #cg4 ,,gay ,,lussac',s ,,mountain ,,barometer4 #ch4 ,,fortin',s ,,mountain ,,barometer4 #ci4 ,,newman',s ,,mountain ,,barometer4 #dj4 ,,negretti ,,and ,,zambra',s ,,patent ,,mountain ,,and ,,other ,,barometers4 #da4 ,short ,tube ,barometer4 #db4 ,method of ,calculating ,heights by the ,barometer2 ,tables and ,examples4 ,,chapter ,v4 ,,secondary ,,barometers4 #dc4 ,desirability of ,magnifying the ,barometer ,range4 #dd4 ,,howson',s ,,long-,,range ,,barometer4 #de4 ,,mcneil',s ,,long-,,range ,,barometer4 #df4 ,the ,water-glass ,barometer4 #dg4 ,,sympiesometers4 #dh4 ,,aneroids4 #di4 ,,small ,,size ,,aneroids4 #ej4 ,,watch ,,aneroid4 #ea4 ,measurement of ,heights by the ,aneroid2 ,example4 #eb4 ,,metallic ,,barometer4 ,,chapter ,,vi4 ,,instruments ,,for ,,ascertaining ,,temperature4 #ec4 ,temperature4 #ed4 ,thermometric ,substances4 #ee4 ,description of the ,thermometer4 #ef4 ,,standard ,,thermometer4 #eg4 ,method of ascertaining the exact ,boiling ,temperature2 ,tables1 c4 #eh4 ,displacement of the ,freezing ,point4 #ei4 ,the ,scale4 #fj4 ,the method of testing ,thermometers4 #fa4 ,porcelain ,scale-,plates4 #fb4 ,enamelled ,tubes4 #fc4 ,,thermometers ,,of ,,extreme ,,sensitiveness4 #fd4 ,,varieties ,,of ,,thermometers4 #fe4 ,,superheated ,,steam ,,thermometer4 #ff4 ,,thermometer ,,for ,,sugar ,,boiling4 #fg4 ,,earth ,,thermometer4 #fh4 ,,marine ,,thermometer4 ,,chapter ,,vii4 ,,self-,,registering ,,thermometers4 #fi4 ,importance of4 #gj4 ,,rutherford',s ,,maximum ,,thermometer4 #ga4 ,,phillips',s ,,ditto ,,ditto4 #gb4 ,,negretti ,,and ,,zambra',s ,,patent ,,maximum ,,thermometer4 #gc4 ,,rutherford',s ,,alcohol ,,minimum ,,thermometer4 #gd4 ,,horticultural ,,minimum ,,thermometer4 #ge4 ,,baudin',s ,,alcohol ,,minimum ,,thermometer4 #gf4 ,mercurial ,minima ,thermometers desirable4 #gg4 ,,negretti ,,and ,,zambra',s ,,patent ,,mercurial ,,minimum ,,thermometer4 #gh4 ,,negretti ,,and ,,zambra',s ,,second ,,patent ,,mercurial ,,minimum ,,thermometer4 #gi4 ,,casella',s ,,patent ,,mercurial ,,minimum ,,thermometer4 #hj4 ,day and ,night ,thermometer4 #ha4 ,,sixe',s ,,self-,,registering ,,thermometer4 ,,chapter ,,viii4 ,,radiation ,,thermometers4 #hb4 ,solar and ,terrestrial ,radiation considered4 #hc4 ,,solar ,,radiation ,,thermometer4 #hd4 ,,vacuum ,,solar ,,radiation ,,thermometer4 #he4 ,,terrestrial ,,radiation ,,thermometer4 #hf4 ,,aethrioscope4 #hg4 ,,pyrheliometer4 #hh4 ,,actinometer4 ,,chapter ,,ix4 ,,deep-,,sea ,,thermometers4 #hi4 ,,on ,,sixe',s ,,principle4 #ij4 ,,johnson',s ,,metallic ,,thermometer4 ,,chapter ,x4 ,,boiling-,,point ,,thermometers4 #ia4 ,ebullition4 #ib4 ,relation between ,boiling-,point and ,elevation4 #ic4 ,,hypsometric ,,apparatus4 #id4 ,precautions to ensure ,correct ,graduation4 #ie4 ,method of ,calculating ,heights from ,observations with the ,mountain ,thermometer2 ,example4 #if4 ,,thermometers ,,for ,,engineers4 ,,chapter ,,xi4 ,,instruments ,,for ,,ascertaining ,,the ,,humidity ,,of ,,the ,,air4 #ig4 ,hygrometric ,substances4 #ih4 ,,saussure',s ,,hygrometer4 #ii4 ,dew-,point4 #ajj4 ,,drosometer4 #aja4 ,humidity4 #ajb4 ,,leslie',s ,,hygrometer4 #ajc4 ,,daniel',s ,,hygrometer4 #ajd4 ,,regnault',s ,,condenser ,,hygrometer4 #aje4 ,temperature of ,evaporation4 #ajf4 ,,mason',s ,,hygrometer4 #ajg4 ,,self-,,registering ,,hygrometer4 #ajh4 ,causes of ,dew4 #aji4 ,plan of ,exposing ,thermometers4 ,,chapter ,,xii4 ,,instruments ,,used ,,for ,,measuring ,,the ,,rainfall4 #aaj4 ,,howard',s ,,rain-,,gauge4 #aaa4 ,,glaisher',s ,,rain-,,gauge4 #aab4 ,,rain-,,gauge ,,with ,,float4 #aac4 ,,rain-,,gauge ,,with ,,side ,,tube4 #aad4 ,,fitzroy',s ,,rain-,,gauge4 #aae4 ,,self-,,registering ,,rain-,,gauge4 #aaf4 ,the principle of ,measurement4 #aag4 ,position for ,rain-gauge1 c4 #aah4 ,cause of ,rain4 #aai4 ,laws of ,rainfall4 #abj4 ,utility of ,statistics of ,rainfall4 #aba4 ,,new ,,form ,,of ,,rain-,,gauge4 ,,chapter ,,xiii4 ,,apparatus ,,employed ,,for ,,registering ,,the ,,direction1 ,,pressure1 ,,and ,,velocity ,,of ,,the ,,wind4 #abb4 ,,the ,,vane4 #abc4 ,,lind',s ,,wind-,,gauge4 #abd4 ,,harris',s ,,wind-,,gauge4 #abe4 ,,robinson',s ,,anemometer4 #abf4 ,,whewell',s ,,anemometer4 #abg4 ,,osler',s ,,anemometer ,,and ,,pluviometer4 #abh4 ,,beckley',s ,,anemometer4 #abi4 ,,self-,,registering ,,wind-,,gauge4 #acj4 ,anemometric ,observations4 ,,chapter ,,xiv4 ,,instruments ,,for ,,investigating ,,atmospheric ,,electricity4 #aca4 ,,atmospheric ,,electroscope4 #acb4 ,,volta',s ,,electrometer4 #acc4 ,,peltier',s ,,electrometer4 #acd4 ,,bohnenberger',s ,,electroscope4 #ace4 ,,thomson',s ,,electrometer4 #acf4 ,fundamental ,facts4 #acg4 ,lightning ,conductors4 #ach4 ,precautions against ,lightning4 ,,chapter ,,xv4 ,,ozone ,,and ,,its ,,indicators4 #aci4 ,nature of ,ozone4 #adj4 ,,schonbein',s ,,ozonometer4 #ada4 ,,moffat',s ,,ozonometer4 #adb4 ,,clark',s ,,ozone ,,cage4 #adc4 ,distribution and ,effects of ,ozone4 #add4 ,,lancaster',s ,,registering ,,ozonometer4 ,,chapter ,,xvi4 ,,miscellaneous ,,instruments4 #ade4 ,,chemical ,,weather ,,glass4 #adf4 ,,leslie',s ,,differential ,,thermometer4 #adg4 ,,romford',s ,,differential ,,thermometer4 #adh4 ,,glaisher',s ,,thermometer ,,stand4 #adi4 ,,thermometer ,,screen1 ,,for ,,use ,,at ,,sea4 #aej4 ,,anemoscope4 #aea4 ,,evaporating ,,dish1 ,,or ,,gauge4 #aeb4 ,,admidometer4 #aec4 ,,cloud ,,reflector4 #aed4 ,,sunshine ,,recorder4 #aee4 ,,set ,,of ,,portable ,,instruments4 #aef4 ,,implements4 #aeg4 ,,hydrometer4 #aeh4 ,,newman',s ,,self-,,registering ,,tide-,,gauge4 ,,tables4 ,,page ,table of ,corrections1 for ,capillary ,depression of the ,mercury in ,boiled and in ,unboiled ,barometer-,tubes #f ,tables for ,deducing ,heights by means of the ,barometer3-- ,no4 #a4 ,approximate ,height due to ,barometric ,pressure #db ,no4 #b4 ,correction for ,mean ,temperature of ,air #dd ,no4 #c4 ,correction due to ,latitude #dd ,no4 #d4 ,correction due to ,approximate ,elevation #de ,tables for ,determining the ,temperature of the ,vapour of ,boiling ,water at any ,place3-- ,no4 #e4 ,factor due to ,latitude #fb ,no4 #f4 ,temperature and ,tension #fb ,table of ,temperature of the ,soil #fi ,table of ,difference of ,elevation corresponding to a fall of #a deg4 in the ,boiling-point of ,water #ih ,table showing ,proportion of ,salt for various ,boiling ,temperatures of ,sea-,water #ajj ,table for finding the ,degree of ,humidity from ,observations with ,mason's ,hygrometer #ajh ,table showing ,amount and ,duration of ,rain at ,london1 in #ahfb #aab ,table of ,average ,british ,rainfall in ,westerly1 ,central1 and ,easterly districts #aad ,table showing ,force of ,wind1 for use with ,lind's ,wind-,gauge #aah ,tables for ,correcting ,observations made with-- ,brass ,hydrometers #adb ,glass ,hydrometers #adc ,,addenda4 ,,page #a4 ,rule for converting ,millimetres into ,inches1 et vice versa #adf #b4 ,old ,french ,lineal ,measure1 with ,english ,equivalents #adf #c4 ,rule for finding ,diameter of ,bore of ,barometer ,tube #adf #d4 ,wind ,scales #adg #e4 ,letters to denote the ,state of the ,weather #adg #f4 ,table of ,expansion of ,bodies #adh #g4 ,table of ,specific ,gravity of ,bodies #adh #h4 ,important ,temperatures #adh #i4 ,table of ,meteorological ,elements1 forming ,exponents of the ,climate of ,london #adi #aj4 ,list of ,works on ,meteorology #aea ,,meteorological ,,instruments4 ,in the pursuits and investigations of the science of ,meteorology1 which is essentially a science of observation and experiment1 instruments are required for ascertaining1 #a4 the pressure of the atmosphere at any time or place2 #b4 the temperature of the air2 #c4 the absorption and radiation of the sun's heat by the earth's surface2 #d4 the humidity of the air2 #e4 the amount and duration of rainfall2 #f4 the direction1 the horizontal pressure1 and the velocity of winds2 #g4 the electric condition of the atmosphere1 and the prevalence and activity of ozone4 ,,chapter ,i4 ,,instruments ,,for ,,ascertaining ,,the ,,atmospheric ,,pressure4 ,illustration3 ,fig4 #a4 #a4 ,principle of the ,barometer4--,the first instrument which gave the exact measure of the pressure of the atmosphere was invented by ,torricelli1 in #afdc4 ,it is constructed as follows3--,a glass tube1 ,,cd 7fig4 #a71 about #cd inches long1 and from two to four-tenths of an inch in diameter of bore1 having one end closed1 is filled with mercury4 ,in a cup1 ,b1 a quantity of mercury is also poured4 ,then1 placing a finger securely over the open end1 ,c1 invert the tube vertically over the cup1 and remove the finger when the end of the tube dips into the mercury4 ,the mercury in the tube then partly falls out1 but a column1 ,,ab1 about #cj inches in height1 remains supported4 ,this column is a weight of mercury1 the pressure of which upon the surface of that in the cup is precisely equivalent to the corresponding pressure of the atmosphere which would be exerted in its place if the tube were removed4 ,as the atmospheric pressure varies1 the length of this mercurial column also changes4 ,it is by no means constant in its height2 in fact1 it is very seldom stationary1 but is constantly rising or falling through a certain extent of the tube1 at the level of the sea1 near which the above experiment is supposed to be performed4 ,it is1 therefore1 an instrument by which the fluctuations taking place in the pressure of the atmosphere1 arising from changes in its weight and elasticity1 can be shown and measured4 ,it has obtained the name ,barometer1 or measurer of heaviness1--a word certainly not happily expressive of the utility of the invention4 ,if the bore of the barometer tube be uniform throughout its length1 and have its sectional area equal to a square inch1 it is evident that the length of the column1 which is supported by the pressure of the air1 expresses the number of cubic inches of mercury which compose it4 ,the weight of this mercury1 therefore1 represents the statical pressure of the atmosphere upon a square inch of surface4 ,in ,england the annual mean height of the barometric column1 reduced to the sea-level and to the temperature of #cb deg4 ,fahrenheit1 is about #bi4ie inches4 ,a cubic inch of mercury at this temperature has been ascertained to weigh #j4dhifg lbs4 avoirdupois4 ,hence1 #bi4ie x #j4dhifg #ad4fg lbs41 is the mean value of the pressure of the atmosphere on each square inch of surface1 near the sea-level1 about the latitude of #ej degrees4 ,nearer the equator this mean pressure is somewhat greater2 nearer the poles1 somewhat less4 ,for common practical calculations it is assumed to be #ae lbs4 on the square inch4 ,when it became apparent that the movements of the barometric column furnished indications of the probable coming changes in the weather1 an attempt was made to deduce from recorded observations the barometric height corresponding to the most notable characteristics of weather4 ,it was found that for fine dry weather the mercury in the barometer at the sea-level generally stood above #cj inches2 changeable weather happened when it ranged from #cj to #bi inches1 and when rainy or stormy weather occurred it was even lower4 ,hence1 it became the practice to place upon barometer scales words indicatory of the weather likely to accompany1 or follow1 the movements of the mercury2 whence the instruments bearing them obtained the name ,weather ,glasses4 #b4 ,construction of ,barometers4--,in order that the instrument may be portable1 it must be made a fixture and mounted on a support2 and1 further1 to render it scientifically or even practically useful1 many precautions are required in its construction4 ,the following remarks apply to the construction of all barometers3--,mercury is universally employed1 because it is the heaviest of fluids1 and therefore measures the atmospheric pressure by the shortest column4 ,water barometers have been constructed1 and they require to be at least #cd feet long4 ,oil1 or other fluids1 might be used4 ,mercury1 however1 has other advantages3 it has feeble volatility1 and does not adhere to glass1 if pure4 ,oxidised1 or otherwise impure mercury1 may adhere to glass2 moreover1 such mercury would not have the density of the pure metal1 and therefore the barometric column would be either greater or less than it should be4 ,the mercury of commerce generally contains lead2 sometimes traces of iron and sulphur4 ,it is necessary1 therefore1 for the manufacturer to purify the mercury2 and this is done by washing it with diluted acetic1 or sulphuric acid1 which dissolves the impurities4 ,no better test can be found for ascertaining if the mercury be pure than that of filling a delicate thermometer tube2 if1 on exhausting the air from this thermometer1 the mercury will freely run up and down the bore1 which is probably one thousandth of an inch in diameter1 the mercury from which this thermometer was made will be found fit for any purpose1 and with it a tube may be filled and boiled1 not only of one inch1 but even of two inches diameter4 ,in all barometers it is requisite that the space above the mercurial column should be completely void of air and aqueous vapour1 because these gases1 by virtue of their elasticity1 would depress the column4 ,to exclude these the mercury is introduced1 and boiled in the tube1 over a charcoal fire1 kept up for the purpose4 ,in this manner the air and vapour which adhere to the glass are expanded1 and escape away4 ,one can tell whether a barometer has been properly boiled1 as it is termed1 by simply holding the tube in a slanting direction and allowing the mercury to strike the top4 ,if the boiling has been well performed1 the mercury will give a clear1 metallic sound2 if not1 a dull1 flat sound1 showing some air to be present4 ,when the mercury in a barometer tube rises or falls1 the level of the mercury in the cup1 or cistern1 as it is generally termed1 falls or rises by a proportionate quantity1 which depends upon the relative areas of the interior of the tube and of the cistern4 ,it is necessary that this should be taken into consideration in ascertaining the exact height of the column4 ,if a fixed scale is applied to the tube1 the correct height may be obtained by applying a correction for capacity4 ,a certain height of the mercury is ascertained to be accurately measured by the scale1 and should be marked on the instrument as the neutral point4 ,above this point the heights measured are all less1 and below1 all more1 than they should be4 ,the ratio between the internal diameters of the tube and cistern 7which should also be stated on the instrument1 as1 for instance1 capac4 #a_/ej7 supplies the data for finding the correction to be applied4 ,this correction is obviated by constructing the cistern so as to allow of the surface of the mercury in it being adjustable to the commencement of the fixed scale1 as by ,fortin's or ,negretti's plan4 ,it is also unnecessary in barometers constructed on what is now called the ,kew method4 ,these will all be detailed in their proper place4 ,the tube1 being fixed to the cistern1 may have a moveable scale applied to it4 ,but such an arrangement requires the utmost care and skill in observing1 and is seldom seen except in first-class ,observatories4 ,illustration3 ,fig4 #b4 #c4 ,fortin's ,barometer4--,fortin's plan of constructing a barometer cistern is shown in fig4 #b4 ,the cistern is formed of a glass cylinder1 which allows of the level of the mercury within being seen4 ,the bottom of the cylinder is made of sheep-skin or leather1 like a bag1 so as to allow of being pushed up or lowered by means of a screw1 ,d ,b1 worked from beneath4 ,this screw moves through the bottom of a brass cylinder1 ,c ,c1 which is fixed outside1 and protects the glass cylinder containing the mercury4 ,at the top of the interior of the cistern is fixed a small piece of ivory1 ,a1 the point of which exactly coincides with the zero of the scale4 ,this screw and moveable cistern-bottom serve also to render the barometer portable1 by confining the mercury in the tube1 and preventing its coming into the cistern1 which is thus made too small to receive it4 #d4 ,,standard ,,barometer4 ,fig4 #c represents a ,standard ,barometer on ,fortin's principle4 ,the barometer tube is enclosed and protected by a tube of brass extending throughout its whole length2 the upper portion of the brass tube has two longitudinal openings opposite each other2 on one side of the front opening is the barometrical scale of ,english inches1 divided to show1 by means of a vernier1 #a_/ejjth of an inch2 on the opposite side is sometimes divided a scale of ,french millimetres1 reading also by a vernier to #a_/ajth of a millimetre 7see directions for reading the vernier1 page #g74 ,a thermometer1 ,c1 is attached to the frame1 and divided to degrees1 which can be read to tenths2 it is necessary for ascertaining the temperature of the instrument1 in order to correct the observed height of the barometer4 ,illustration3 ,fig4 #c4 ,as received by the observer1 the barometer will consist of two parts1 packed separately for safety in carriage1--#ast1 the barometer tube and cistern1 filled with mercury1 the brass tube1 with its divided scale and thermometer2 and #bnd1 a mahogany board1 with bracket at top1 and brass ring with three adjusting screws at bottom4 ,directions for fixing the ,barometer4--,in selecting a position for a barometer1 care should be taken to place it so that the sun cannot shine upon it1 and that it is not affected by direct heat from a fire4 ,the cistern should be from two to three feet above the ground1 which will give a height for observing convenient to most persons4 ,a standard barometer should be compared with an observatory standard of acknowledged accuracy1 to determine its index error2 which1 as such instruments are graduated by micrometrical apparatus of great exactitude1 will be constant for all parts of the scale4 ,it should be capable of turning on its axis by a movement of the hand1 so that little difficulty can ever be experienced in obtaining a good light for observation4 ,having determined upon the position in which to place the instrument1 fix the mahogany board as nearly vertical as possible1 and ascertain if the barometer is perfect and free from air1 in the following manner3--lower the screw at the bottom of the cistern several turns1 so that the mercury in the tube1 when held upright1 may fall two or three inches from the top2 then slightly incline the instrument from the vertical position1 and if the mercury in striking the top elicit a sharp tap1 the instrument is perfect4 ,supposing the barometer to be in perfect condition1 as it is almost sure to be1 it is next suspended on the brass bracket1 its cistern passing through the ring at bottom1 and allowed to find its vertical position1 after which it is firmly clamped by means of the three thumb-screws4 ,to ,remove the ,instrument when fixed to another ,position4--,if it should be necessary to remove the barometer1--first1 by means of the adjusting screw1 drive the mercury to the top of the tube1 turning it gently when it is approaching the top1 and cease directly any resistance is experienced2 next1 remove from the upper bracket or socket2 lift the instrument and invert it1 carrying it with its lower end upwards4 ,directions for taking an ,observation4--,before making an observation1 the mercury in the cistern must be raised or lowered by means of the thumb-screw1 ,f1 until the ivory point1 ,e1 and its reflected image in the mercury1 ,d1 are just in contact2 the vernier is then moved by means of the milled head1 until its lower termination just excludes the light from the top of the mercurial column2 the reading is then taken by means of the scale on the limb and the vernier4 ,the vernier should be made to read upward in all barometers1 unless for a special object1 as this arrangement admits of the most exact setting4 ,in observing1 the eye should be placed in a right line with the fore and back edges of the lower termination of the vernier2 and this line should be made to form a tangent to the apex of the mercurial column4 ,a small reflector placed behind the vernier and moving with it1 so as to assist in throwing the light through the back slit of the brass frame on to the glass tube1 is advantageous2 and the observer's vision may be further assisted by the aid of a reading lens4 ,the object is1 in these ,standard ,barometers1 to obtain an exact reading1 which can only be done by having the eye1 the fore part of the zero edge of the vernier1 the top of the mercurial column1 and the back of the vernier1 in the same horizontal plane4 ,uniformity of ,calibre4--,the diameter of that part of the tube through which the oscillations of the mercury will take place is very carefully examined to insure uniformity of calibre1 and only those tubes are used which are as nearly as possible of the same diameter throughout4 ,the size of the bore should be marked on the frame of the barometer in tenths and hundredths of an inch4 ,a correction due to capillary action1 and depending on the size of the tube1 must be applied to the readings4 #e4 ,correction due to ,capillarity4--,when an open tube of small bore is plunged into mercury1 the fluid will not rise to the same level inside as it has outside4 ,hence1 the effect of capillary action is to depress the mercurial column2 and the more so the smaller the tube4 ,the following table gives the correction for tubes in ordinary use3-- ,diameter ,depression1 in ,depression1 in of tube4 boiled tubes4 unboiled tubes4 ,,inch4 ,,inch4 ,,inch4 #j4fj #j4jjb #j4jjd #j4ee #j4jjc #j4jje #j4ej #j4jjc #j4jjg #j4de #j4jje #j4jaj #j4dj #j4jjg #j4jae #j4ce #j4jaj #j4jba #j4ae #j4jdd #j4jbi #j4aj #j4jgj #j4jda #j4cj #j4jad #j4jeh #j4be #j4jbj #j4jhf #j4bj #j4jbi #j4adj ,this correction is always additive to the observed reading of the barometer4 #f4 ,correction due to ,temperature4--,in all kinds of mercurial barometers attention must be given to the temperature of the mercury4 ,as this metal expands and contracts very much for variations of temperature1 its density alters correspondingly1 and in consequence the height of the barometric column also varies4 ,to ascertain the temperature of the mercury1 a thermometer is placed near the tube1 and is sometimes made to dip into the mercury in the cistern4 ,the freezing point of water1 #cb deg4,f41 is the temperature to which all readings of barometers must be reduced1 in order to make them fairly comparable4 ,the reduction may be effected by calculation1 but the practical method is by tables for the purpose2 and for these tables we refer the reader to the works mentioned at the end of this book4 #g4 ,correction due to ,height above the ,half-tide ,level4--,further1 in order that barometrical observations generally may be made under similar circumstances1 the readings1 corrected for capacity1 capillarity1 and temperature1 should be reduced to what they would be at the sea-level1 by adding a correction corresponding to the height above the mean level of the sea1 or of half-tide4 ,for practical purposes of comparison with barometric pressure at other localities1 add one-tenth of an inch to the reading for each hundred feet of elevation above the sea4 ,for scientific accuracy this will not suffice1 but a correction must be obtained by means of ,schuckburg's formula1 or tables computed therefrom4 #h4 ,the ,barometer ,vernier4--,the vernier1 an invaluable contrivance for measuring small spaces1 was invented by ,peter ,vernier1 about the year #afcj4 ,the barometer scale is divided into inches and tenths4 ,the vernier enables us to accurately subdivide the tenths into hundredths1 and1 in first-class instruments1 even to thousandths of an inch4 ,it consists of a short scale made to pass along the graduated fixed scale by a sliding motion1 or preferably by a rack-and-pinion motion1 the vernier being fixed on the rack1 which is moved by turning the milled head of the pinion4 ,the principle of the vernier1 to whatever instrumental scale applied1 is that the divisions of the moveable scale are to those in an equal length of the fixed scale in the proportion of two numbers which differ from each other by unity4 ,illustration3 ,fig4 #d4 ,illustration3 ,fig4 #e4 ,the scales of standard barometers are usually divided into half-tenths1 or 4#je1 of an inch1 as represented1 in fig4 #e1 by ,,ab4 ,the vernier1 ,,cd1 is made equal in length to twenty-four of these divisions1 and divided into twenty-five equal parts2 consequently one space on the scale is larger than one on the vernier by the twenty-fifth part of 4#je1 which is 4#jjb inch1 so that such a vernier shows differences of 4#jjb inch4 ,the vernier of the figure reading upwards1 the lower edge1 ,d1 will denote the top of the barometer column2 and is the zero of the vernier scale4 ,in fig4 #d1 the zero being in line exactly with #bi inches and five-tenths of the fixed scale1 the barometer reading would be #bi4ejj inches4 ,it will be seen that the vernier line1 a1 falls short of a division of the scale by1 as we have explained1 4#jjb inch2 b1 by 4#jjd2 c1 by 4#jjf2 d1 by 4#jjh2 and the next line by one hundredth4 ,if1 then1 the vernier be moved so as to make a coincide with z1 on the scale1 it will have moved through 4#jjb inch2 and if #a on the vernier be moved into line with y on the scale1 the space measured will be 4#jaj4 ,hence1 the figures #a1 #b1 #c1 #d1 #e on the vernier measure hundredths1 and the intermediate lines even thousandths of an inch4 ,in fig4 #e1 the zero of the vernier is intermediate #bi4fe and #bi4gj on the scale4 ,passing the eye up the vernier and scale1 the second line above #c is perceived to lie evenly with a line of the scale4 ,this gives 4#jc and 4#jjd to add to #bi4fe1 so that the actual reading is #bi4fhd inches4 ,it may happen that no line on the vernier accurately lies in the same straight line with one on the scale2 in such a case a doubt will arise as to the selection of one from two equally coincident1 and the intermediate thousandth of an inch should be taken4 ,for the ordinary purposes of the barometer as a weather-glass1 such minute measurement is not required4 ,hence1 in household and marine barometers the scale need only be divided to tenths1 and the vernier constructed to measure hundredths of an inch4 ,this is done by making the vernier either #i or #aa-ajths of an inch long1 and dividing it into ten equal parts4 ,the lines above the zero line are then numbered from #a to #aj2 sometimes the alternate divisions only are numbered1 the intermediate numbers being very readily inferred4 ,hence1 if the first line of the vernier agrees with one on the scale1 the next must be out one-tenth of a tenth1 or 4#ja of an inch from agreement with the next scale line2 the following vernier line must be 4#jb out1 and so on4 ,consequently1 when the vernier is set to the mercurial column1 the difference shown by the vernier from the tenth on the scale is the hundredths to be added to the inches and tenths of the scale4 ,a little practice will accustom a person to set and read any barometer quickly2 an important matter where accuracy is required1 as the heat of the body1 or the hand1 is very rapidly communicated to the instrument1 and may vitiate1 to some extent1 the observation4 #i4 ,,self-,,compensating ,,standard ,,barometer4 ,this barometer has been suggested to ,messrs4 ,negretti and ,zambra by ,wentworth ,erk1 ,esq4 ,it consists of a regular barometer2 but attached to the vernier is a double rack worked with one pinion1 so that in setting or adjusting the vernier in one position1 the second rack moves in directly the opposite direction1 carrying along with it a plug or plunger the exact size of the internal diameter of the tube dipping in the cistern1 so that whatever the displacement that has taken place in the cistern1 owing to the rise or fall of the mercury1 it is exactly compensated by the plug being more or less immersed in the mercury1 so that no capacity correction is required4 ,a barometer on this principle is1 however1 no novelty1 for at the ,royal ,society's room a very old instrument may be seen reading somewhat after the same manner4 ,illustration3 ,fig4 #f4 ,fig4 #f is an illustration of the appearance of this instrument4 ,the cistern is so constructed that the greatest amount of light is admitted to the surface of the mercury4 #aj4 ,,barometer ,,with ,,electrical ,,adjustment4 ,this barometer is useful to persons whose eyesight may be defective2 and is capable of being read off to greater accuracy than ordinary barometers1 as will be seen by the following description3--,the barometer consists of an upright tube dipping into a cistern1 so contrived1 that an up-and-down movement1 by means of a screw1 can be imparted to it4 ,in the top of the tube a piece of platina wire is hermetically sealed4 ,the cistern also has a metallic connection1 so that by means of covered copper wires 7in the back of the frame7 a circuit is established2 another connection also exists by means of a metallic point dipping into the cistern4 ,the circuit1 however1 can be cut off from this by means of a switch placed about midway up the frame2 on one side of the tube is placed a scale of inches2 a small circular vernier1 divided into #ajj parts1 is connected with the dipping point1 and works at right angles with this scale4 ,to set the instrument in action for taking an observation1 a small battery is connected by means of two small binding screws at the bottom of the frame4 ,the switch is turned upwards1 thereby disconnecting the dipping point2 the cistern is then screwed up1 so that the mercury in the tube is brought into contact with the platina wire at the top2 the instant this is effected the magnetic needle seen on the barometer will be deflected4 ,the switch is now turned down2 by so doing the connection with the upper wire or platina is cut off1 and established instead only between the dipping point carrying the circular vernier and the bottom of the cistern2 the point is now screwed by means of the milled head until the needle is again deflected4 ,we may now be sure that the line on the circular vernier that cuts the division on the scale is the exact height of the barometer4 ,although the description here given may seem somewhat lengthy1 the operation itself is performed in less time than would be taken in reading off an ordinary instrument4 #aa4 ,,pediment ,,barometers4 ,illustration3 ,fig4 #g4 ,illustration3 ,fig4 #h4 ,illustration3 ,fig4 #i4 ,illustration3 ,fig4 #aj4 ,illustration3 ,fig4 #aa4 ,these ,barometers1 generally for household purposes1 are illustrated by figs4 #g to #aa4 ,they are intended chiefly for weather glasses1 and are manufactured to serve not only a useful1 but an ornamental purpose as well4 ,they are usually framed in wood1 such as mahogany1 rosewood1 ebony1 oak or walnut1 and can be obtained either plain or handsomely and elaborately carved and embellished1 in a variety of designs1 so as to be suitable for private rooms1 large halls1 or public buildings4 ,the scales to the barometer and its attached thermometer may be ivory1 porcelain1 or silvered metal4 ,it is not desirable that the vernier should read nearer than one-hundredth of an inch4 ,two verniers and scales may be fitted one on either side of the mercurial column1 so that one can denote the last reading1 and thus show at a glance the extent of rise or fall in the interval4 ,the scale and thermometer should be covered with plate glass4 ,a cheap instrument has an open face and plain frame1 with sliding vernier instead of rack-and-pinion motion4 ,the barometer may or may not have a moveable bottom to the cistern1 with screw for the purpose of securing the mercury for portability4 ,the cistern should not1 however1 require adjustment to a zero or fiducial point4 ,it should be large enough to contain the mercury1 which falls from #ca to #bg inches1 without any appreciable error on the height read off on the scale4 #ab4 ,the ,words on the ,scale4--,the following words are usually engraved on the scales of these barometers1 although they are not now considered of so much importance as formerly3-- ,at #ca inches ,very dry4 #cj4e ,settled fair4 #cj ,fair4 #bi4e ,changeable4 #bi ,rain4 #bh4e ,much rain4 #bh ,stormy4 ,the ,french place upon their barometers a similar formula3-- ,at #ghe millimetres ,tres-sec4 #ggf ,beau-fixe4 #gfg ,beau temps4 #geh ,variable4 #gdi ,pluie ou vent4 #gdj ,grande pluie4 #gca ,tempete4 ,manufacturers of barometers have uniformly adopted these indications for all countries1 without regard to the elevation above the sea1 or the different geographical conditions2 and as it can readily be shown that the height and variations of the barometer are dependent on these1 it follows that barometers have furnished indications which1 under many circumstances1 have been completely false4 ,even in this country1 and near the sea-level1 storms are frequent with the barometer not below #bi2 rain is not uncommon with the glass at #cj2 even fine weather sometimes occurs with a low pressure2 while it is evident that at an elevation of a few thousand feet the mercury would never rise to #cj inches2 hence1 according to the scale1 there should never be fair weather there4 ,if tempests happened as seldom in our latitude as the barometer gets down to #bh inches1 the maritime portion of the community at least would be happy indeed4 ,these words have long been ridiculed by persons acquainted with the causes of the barometric fluctuations2 nevertheless opticians continue to place them on the scales1 evidently only because they appear to add to the importance of the instrument in the eyes of those who have not learned their general inutility4 ,in different regions of the world1 the indications of the barometer are modified by the conditions peculiar to the geographical position and elevation above the sea1 and it is necessary to take account of these in any attempt to found rules of general utility in connection with the barometer as a weather guide4 ,all that can be said in favour of these words is1 that within a few hundred feet of the sea-level1 when the column rises or falls gradually during two or three days towards ,fair or ,rain1 the indications they afford of the coming weather are generally extremely probable2 but when the variations are quick1 upward or downward1 they presage unsettled or stormy weather4 ,admiral ,fitz,roy writes3--,the words on the scales of barometers should not be so much regarded1 for weather indications1 as the rising or falling of the mercury2 for if it stands at ,changeable1 and then rises a little towards ,fair1 it presages a change of wind or weather1 though not so great as if the mercury had risen higher2 and1 on the contrary1 if the mercury stands above ,fair and falls1 it presages a change1 though not to so great a degree as if it had stood lower2 besides which1 the direction and force of wind are not in any way noticed4 ,it is not from the point at which the mercury stands that we are alone to form a judgment of the state of the weather1 but from its rising or falling2 and from the movements of immediately preceding days as well as hours1 keeping in mind effects of change of direction and dryness1 or moisture1 as well as alteration of force or strength of wind4#a #ac4 ,correction due to ,capacity of ,cistern4--,these barometers1 having no adjustment for the zero of the scale1 require a correction for the varying level of the mercury in the cistern1 when the observations are required for strict comparison with other barometric observations1 or when they are registered for scientific purposes2 but for the common purpose of predicting the weather1 this correction is unnecessary4 ,the neutral point1 and the ratio of the bore of the tube to the diameter of the cistern1 must be known 7see p4 #c74 ,then the capacity correction1 as it is termed1 is found as follows3--,take the fractional part1 expressed by the capacity ratio1 of the difference between the observed reading and the height of the neutral point2 then1 if the mercury stand below the neutral point1 subtract this result from the reading2 if it stand above1 add it to the reading4 ,for example1 suppose the neutral point to be #bi4ie inches1 and the capacity ratio #a_/ej1 required the correction when the barometer reads #cj4gh4 ,here #cj4gh - #bi4ie #j4hc ,correction #j4hc_/ej #j4jb nearly4 ,scale reading #cj4gh ----- ,correct reading #cj4hj ,of course the correction could as easily be found to three decimal places1 if desirable4 ,it is evident that the correction is more important the greater the distance of the top of the mercury from the neutral point4 #ad4 ,,public ,,barometers4 ,since the increased attention paid to the signs of forthcoming weather of late years1 and the good which has resulted therefrom to farmers1 gardeners1 civil engineers1 miners1 fishermen1 and mariners generally1 by forewarning of impending wet or stormy weather1 the desirability of having good barometers exposed in public localities has become evident4 ,barometers may now be seen attached to drinking fountains1 properly protected1 and are frequently consulted by the passers-by4 ,but it is among those whose lives are endangered by sudden changes in the weather1 fishermen especially1 that the warning monitor is most urgently required4 ,many poor fishing villages and towns have therefore been provided by the ,board of ,trade1 at the public expense1 and through the humane effort of ,admiral ,fitz,roy1 with first-class barometers1 each fixed in a conspicuous position1 so as to be easily accessible to all who desire to consult it4 ,following this example1 the ,royal ,national ,life ,boat ,institution has supplied each of its stations with a similar storm warner2 the ,duke of ,northumberland and the ,british ,meteorological ,society have erected several on the coast of ,northumberland2 and many other individuals have presented barometers to maritime places with which they are connected4 ,these barometers have all been manufactured by ,messrs4 ,negretti and ,zambra4 ,the form given to the instrument seems well adapted for public purposes4 ,illustration3 ,fig4 #ab4 #ae4 ,fishery or ,sea-coast ,barometers4--,fig4 #ab gives a representation of these coast and fishery barometers4 ,the frame is of solid oak1 firmly screwed together4 ,the scales are very legibly engraved on porcelain by ,negretti and ,zambra's patent process4 ,the thermometer is large1 and easily read2 and as this instrument is exposed1 it will indicate the actual temperature sufficiently for practical purposes4 ,the barometer tube is three-tenths of an inch in diameter of bore1 exhibiting a good column of mercury2 and the cistern is of such capacity1 in relation to the tube1 that the change of height in the surface of the mercury in the cistern corresponding to a change of height of three inches of mercury in the tube1 is less than one-hundredth of an inch1 and therefore1 as the readings are only to be made to this degree of accuracy1 this small error is of no importance4 ,the cistern is made of boxwood1 which is sufficiently porous to allow the atmosphere to influence the mercurial column2 but the top is plugged with porous cane1 to admit of free and certain play4 #af4 ,admiral ,fitz,roy's ,scale ,words4--,the directions given on the scales of these barometers were drawn up by ,admiral ,fitz,roy1 ,f4,r4,s4 ,they appear to be founded on the following considerations3-- ,supposing a compass diagram1 with the principal points laid down1 the ,n4,e4 is the wind for which the barometer stands highest2 for the ,s4,w4 wind it is lowest4 ,this is found to be so in the great majority of cases2 but there are exceptions to this1 as to all rules4 ,the ,n4,e4 and ,s4,w4 may therefore be regarded as the poles of the winds1 being opposite each other4 ,when the wind veers from the ,s4,w4 through ,w4 and ,n4 to ,n4,e41 the barometer gradually rises2 on the contrary1 when the wind veers from ,n4,e4 and ,e4 to ,s4,e41 ,s4 and ,s4,w41 the mercury falls4 ,a similar curious law exists in relation to the veering of the wind1 and the action of the thermometer4 ,as the wind veers from the ,s4,w4 to ,w4 and ,n41 the thermometer falls2 as it veers from ,n4,e4 to ,e4 and ,s41 it rises1 because the wind gets from a colder to a warmer quarter4 ,the polar winds are cold1 dry1 and heavy4 ,those from the equatorial regions are warm1 moist1 and comparatively light4 ,these laws have been clearly developed and expressed by ,professor ,dove in his work on the ,law of ,storms4 ,the warm winds of ,europe are those which bring the greatest quantity of rain1 as they blow from the ocean1 and come heavily laden with moisture4 ,the cold winds1 besides containing less moisture1 blow more from the land4 ,the weight of the vapour of the warm winds tends to raise the barometric column2 but1 at the same time1 the increased dilatation of the air tends to lower it4 ,this latter influence being the stronger1 the barometer always falls for these winds2 and in regions where they traverse a large extent of land1 retain their heat1 and become necessarily very dry1 the fall in the barometer will be greater4 ,admiral ,fitz,roy's words for the scales of barometers for use in northern latitudes1 then1 are as follows3-- ,,rise4 ,,fall4 ,,for ,,for ,n4 ,,ely4 ,s4 ,,wly4 ,,nw4--,n4--,e4 ,,se4--,s4--,w4 ,,dry ,,wet ,,or ,,or ,,less ,,more ,,wind4 ,,wind4 ------- ------- ,,except ,,except ,,wet ,,from ,,wet ,,from ,n4 ,,ed4 ,n4 ,,ed4 ------- ------- ,long foretold1 long last2 ,first rise after low1 ,short notice1 soon past4 ,foretells stronger blow4 ,it will be perceived that the exception in each case applies to ,n4,e4 winds4 ,the barometer may fall with north-easterly winds1 but they will be violent and accompanied with rain1 hail1 or snow2 again1 it will rise with these winds accompanied with rain1 when they are light1 and bring only little rain4 ,it rises1 however1 highest with the dry and light ,n4,e4 winds4 ,these directions are very practically useful2 they provide for geographical position--also for elevation above the sea--since they are not appended to any particular height of the column4 ,they are suited to the northern hemisphere generally1 as well as around the ,british ,isles4 ,the same directions are adapted to the southern hemisphere1 by simply substituting for the letter ,n the letter ,s1 reading south for north1 and vice versa4 ,south of the equator the cold winds come from the south2 the warm1 from the north4 ,the ,s4,e4 wind in the southern hemisphere corresponds to the ,n4,e4 in the northern4 ,the laws there are1 while the wind veers from ,s4,e4 through ,e4 to ,n4 and ,n4,w41 the barometer falls and the thermometer rises4 ,as the wind veers from ,n4,w4 through ,w4 and ,s4 to ,s4,e41 the barometer rises and the thermometer falls4 #ag4 ,instructions for the ,sea-coast ,barometer4--,the directions for fixing the barometer1 and making it portable when it has to be removed1 should be attended to carefully4 ,the barometer should be suspended against a frame or piece of wood1 so that light may be seen through the tube4 ,otherwise a piece of paper1 or a white place1 should be behind the upper or scale part of the tube4 ,when suspended on a hook1 or stout nail1 apply the milled-head key 7which will be found just below the scales7 to the square brass pin at the lower end of the instrument1 and turn gently toward the left hand till the screw stops2 then take off the key and replace it for use1 near the scale1 as it was before4 ,the cistern bottom being thus let down1 the mercury will sink to its proper level quickly4 ,in removing this barometer it is necessary to slope it gradually1 till the mercury is at the top of the tube1 and then1 with the instrument reversed1 to screw up the cistern bottom1 or bag1 by the key1 used gently1 till it stops4 ,it will then be portable1 and may be carried with the cistern end upwards1 or lying flat2 but it must not be jarred1 or receive a concussion4 #ah4 ,french ,sea-coast ,barometer4--,the ,french have imitated this form of barometer for coast service1 and have translated ,admiral ,fitz,roy's indications for the scale as follows3-- ,,la ,,la ,,hausse ,,baisse ,,indique4 ,,indique4 --------- --------- ,,des ,,vents ,,de ,,la ,,des ,,vents ,,de ,,la ,,partie ,,du ,,partie ,,du ,n4,e4 ,s4,o4 7,,du ,n4,o4 a l',e7 7,,du ,s4,e4 a l',o47 7,,par ,,le ,,nord4 7 7,,par ,,le ,,sud4 7 ,,de ,,la ,,de ,,secheresse4 ,l',,humidite4 --------- --------- ,,un ,,vent ,,un ,,vent ,,plus ,,faible ,,plus ,,fort ,,excepte ,s',,il ,,pleut ,,excepte ,s',,il ,,pleut ,,avec ,,de ,,fortes ,,brises ,,avec ,,de ,,petites ,,brises ,,du ,n4,e4 ,,du ,n4,e4 --------- --------- ,mouvements lents1 ,le commencement ,temps durable4 de la hausse1 --------- apres une grande ,mouvements rapides1 baisse presage ,temps variable4 un ,vent violent4 ,,marine ,,barometers4 #ai4 ,the ,common ,form4--,the barometer is of great use to the mariner1 who1 by using it as a weather glass1 is enabled to foresee and prepare for sudden changes in the weather4 ,for marine purposes1 the lower portion of the glass tube of the barometer must be contracted to a fine bore1 to prevent oscillation in the mercurial column1 which would otherwise be occasioned by the movements of the ship4 ,this tube is cemented to the cistern1 which is made of boxwood1 and has a moveable leathern bottom1 for the purpose of rendering the instrument portable1 by screwing up the mercury compactly in the tube4 ,the tube is enclosed in a mahogany frame1 which admits of a variety of style in shape1 finish1 and display1 to meet the different fancies and means of purchasers4 ,the frame is generally enlarged at the upper part to receive the scales and the attached thermometer1 which are covered by plate glass4 ,the cistern is encased in brass for protection1 the bottom portion unscrewing to give access to the portable screw beneath the cistern4 ,figs4 #ac and #ad illustrate this form of barometer4 ,marine barometers require to be suspended1 so that they may remain in a vertical position under the changeable positions of a vessel at sea4 ,to effect this they are suspended in gimbals by a brass arm4 ,the gimbals consist of a loose ring fastened by thumb-screws to the middle part of the frame of the barometer1 in front and back4 ,the forked end of the arm supports this ring at the sides1 also by the aid of thumb-screws4 ,hence the superior weight of the cistern end is always sufficient to cause the instrument to move on its bearing screws1 so as always to maintain a perpendicular position2 in fact1 it is so delicately held that it yields to the slightest disturbance in any direction4 ,the other end of the arm is attached to a stout plate1 having holes for screws1 or fitted to slip into a staple or bracket1 by which it may be fixed to any part of the cabin of a ship2 the arm is hinged to the plate1 for the purpose of turning the arm and barometer up whenever it is desirable4 ,illustration3 ,fig4 #ac4 ,illustration3 ,fig4 #ad4 ,other forms of barometer 7to be immediately described7 have superseded this in the ,british ,marine1 but the ,french still give the preference to the wooden frames4 ,they think the barometer can be more securely mounted in wood1 is more portable1 and less liable to be broken by a sudden concussion than if fitted in a metal frame4 ,the ,english deem the ordinary wooden barometers not sufficiently accurate1 owing to the irregular expansion of wood1 arising from its hygrometric properties4 ,some of the ,english opticians have shown that very portable1 and really accurate barometers can be made in brass frames1 and therefore the preference is now given to this latter material4 #bj4 ,the ,kew ,marine ,barometer4--,the form of barometer so-called1 is that recommended by the ,congress of ,brussels1 held in #ahec1 for the purpose of devising a systematic plan of promoting meteorological observations at sea4 ,the materials employed in its construction are mercury1 glass1 iron1 and brass4 ,the upper part of the tube is carefully calibrated to ensure uniformity of bore1 as this is a point upon which the accuracy of the instrument to some extent depends4 ,at sea1 the barometer has never been known to stand above #ca inches1 nor below #bg4 ,these extremes have been attained with instruments of undoubted accuracy1 but they are quite exceptional4 ,it is not necessary1 therefore1 to carry the scales of marine barometers beyond these limits1 but they should not be made shorter4 ,if the vernier is adjusted to read upward1 the scale should extend to #cb inches1 to allow room for the vernier to be set to #ca inches at least4 ,cases have occurred in which this could not be done1 and rare1 but valuable observations have been lost in consequence4 ,if the scale part of the tube be not uniform in bore1 the index error will be irregular throughout the scale4 ,whether the bore of the rest of the tube varies in diameter1 is of no moment4 ,from two to three inches below the measured part1 the bore is contracted very much1 to prevent the pulsations in the mercurial column--called pumping--which1 otherwise1 would occur at sea from the motion of the ship4 ,in ordinary marine barometers1 this contraction extends to the end of the tube4 ,below the contracted part is inserted a pipette--or ,gay ,lussac air-trap--which is a little elongated funnel with the point downwards4 ,its object is to arrest any air that may work in between the glass and the mercury4 ,the bubble of air lodges at the shoulder1 and can go up no farther4 ,it is one of those simple contrivances which turn out remarkably useful4 ,if any air gets into the tube1 it does not get to the top1 and therefore does not vitiate the performance of the barometer2 for the mercury itself works up and down through the funnel4 ,below this1 the tube should not be unnecessarily contracted4 ,illustration3 ,fig4 #ae4 ,the open end of the tube is fixed into an iron cylinder1 which forms the cistern of the barometer4 ,iron has no action upon mercury1 and is therefore used instead of any other metal4 ,one or two holes are made in the top of the cistern1 which are covered on the inside with strong sheep-skin leather1 so as to be impervious to mercury1 but sufficiently porous for the outer air to act upon the column4 ,the cistern is of capacity sufficient to receive the mercury which falls out of the tube until the column stands lower than the scale reads2 and when the tube is completely full1 there is enough mercury to cover the extremity so as to prevent access of air4 ,there is no screw required for screwing up the mercury4 ,the glass tube thus secured to the cistern is protected by a brass tubular frame1 into which the iron cistern fits and screws compactly4 ,cork is used to form bearings for the tube4 ,a few inches above the cistern is placed the attached thermometer4 ,its bulb is enclosed in the frame1 so as to be equally affected by heat with the barometric column4 ,the upper end of the frame is fitted with a cap which screws on1 and embraces a glass shield which rests in a gallery formed on the frame below the scale1 and serves to protect the silvered scale1 as well as the inner tube1 from dust and damp4 ,a ring1 moveable in a collar fixed on the frame above the centre of gravity of the instrument1 is attached to gimbals1 and the whole is supported by a brass arm in the usual manner2 so that the instrument can be moved round its axis to bring any source of light upon it1 and will remain vertical in all positions of the ship4 ,the vernier reads to five-hundredths of an inch4 ,no words are placed upon the scale1 as the old formulary was deemed misleading4 ,the vernier can be set with great exactness1 as light is admitted to the top of the mercury by a front and a back slit in the frame4 ,the lower edge of the vernier should be brought to the top of the mercury1 so as just to shut out the light4 ,it is evident that this form of barometer must be more reliable in its indications than those in wooden frames4 ,the graduations can be accurately made1 and they will be affected only by well-known alterations due to temperature4 ,some think the tube is too firmly held1 and therefore liable to be broken by concussion more readily than that of an inferior instrument4 ,this1 however1 appears a necessary consequence of greater exactness4 ,it is an exceedingly good portable instrument1 and can be put up and taken down very readily4 ,these barometers are preferred to marine barometers in wood1 wherever they have been used4 ,in merchant ships1 and under careful treatment1 they have been found very durable4 ,they may be sent with safety by railway1 packed carefully in a wooden box4 ,directions for ,packing4--,in removing this barometer it is necessary to slope it gradually till the mercury reaches the top of the tube4 ,it is then portable1 if carried cistern end upwards or lying flat4 ,if carried otherwise1 it will very probably be broken by the jerking motion of the heavy mercury in the glass tube4 ,of course it must not be jarred1 or receive concussion4 ,position for ,marine ,barometer4--,admiral ,fitz,roy1 to whose valuable papers we are much indebted1 writes in his ,barometer ,manual3--,it is desirable to place the barometer in such a position as not to be in danger of a side blow1 and also sufficiently far from the deck above to allow for the spring of the metal arm in cases of sudden movements of the ship4 ,if there is risk of the instrument striking anywhere when the vessel is much heeled1 it will be desirable to put some soft padding on that place1 or to check movement in that direction by a light elastic cord2 in fixing which1 attention must be paid to have it acting only where risk of a blow begins1 not interfering otherwise with the free swing of the instrument3 a very light cord attached above1 when possible1 will be least likely to interfere injuriously4 #ba4 ,method of verifying ,marine and other ,barometers4--,in nearly all the barometers which had been employed at sea till recently the index correction varied through the range of scale readings1 in proportion to the difference of capacity between the cistern and the tube4 ,to find the index correction for a land barometer1 comparison with a standard1 at any part of the scale at which the mercury may happen to be1 is generally considered sufficient4 ,to test the marine barometer is a work of much more time1 since it is necessary to find the correction for scale readings at about each half inch throughout the range of atmospheric pressure to which it may be exposed2 and it becomes necessary to have recourse to artificial means of changing the pressure of the atmosphere on the surface of the mercury in the cistern4 ,the barometers to be thus tested are placed1 together with a standard1 in an air-tight chamber1 to which an air-pump is applied1 so that1 by partially exhausting the air1 the standard can be made to read much lower than the lowest pressure to which marine barometers are likely to be exposed2 and by compressing the air it can be made to read higher than the mercury ever stands at the level of the sea4 ,the tube of the standard is contracted similarly to that of the marine barometer1 but a provision is made for adjusting the mercury in its cistern to the zero point4 ,glass windows are inserted in the upper part of the iron air-chamber1 through which the scales of the barometers may be seen2 but as the verniers cannot be moved in the usual way from outside the chamber1 a provision is made for reading the height of the mercury independent of the verniers attached to the scales of the respective barometers4 ,at a distance of some five or six feet from the air-tight chamber a vertical scale is fixed4 ,the divisions on this scale correspond exactly with those on the tube of the standard barometer4 ,a vernier and telescope are made to slide on the scale by means of a rack and pinion4 ,the telescope has two horizontal wires1 one fixed and the other moveable by a micrometer screw1 so that the difference between the height of the column of mercury and the nearest division on the scale of the standard1 and also of all the other barometers placed by the side of it for comparison1 can be measured either with the vertical scale and vernier or the micrometer wire4 ,the means are thus possessed of testing barometers for index error in any part of the scale1 through the whole range of atmospheric pressure to which they are likely to be exposed2 and the usual practice is to test them at every half inch from #bg4e to #ca inches4 ,in this way barometers of various other descriptions have been tested1 and some errors found to be so large that a few barometers read half an inch and upwards too high1 while others read as much too low4 ,in some cases those which were correct in one part of the scale were found to be from half an inch to an inch wrong in other parts4 ,these barometers were of an old and ordinary1 not to say inferior1 construction4 ,in some the mercury would not descend lower than about #bi inches1 owing to a fault very general in the construction of many common barometers till lately in frequent use3--the cistern was not large enough to hold the mercury which descended from the tube in a low atmospheric pressure4 ,when used on shore1 this contraction of the tube causes the marine barometer to be sometimes a little behind an ordinary land barometer1 the tube of which is not contracted4 ,the amount varies according to the rate at which the mercury is rising or falling1 and ranges from #j4jj to #j4jb of an inch4 ,as the motion of the ship at sea causes the mercury to pass more rapidly through the contracted tube1 the readings are almost the same there as they would be if the tube were not contracted1 and in no case do they differ enough to be of importance in maritime use4 ,the cistern of this marine barometer is generally made an inch and a quarter in diameter1 and the scale part of the tube a quarter of an inch in bore4 ,the inches on the scale1 instead of being true1 are shortened by 4#jd of an inch1 in order to avoid the necessity of applying a correction due to the difference of capacity of the tube and cistern4 ,this is done with much perfection1 and the errors of the instruments1 when compared with a standard by the apparatus used at ,kew and ,liverpool ,observatories1 are determined to the thousandth of an inch1 and are invariably very uniform and small4 ,the error so determined includes the correction due to capillarity1 capacity1 and error of graduation1 and forms a constant correction1 so that only one variable correction1 that due to temperature1 need be applied1 when the barometer is suspended near the water line of the ship1 to make the observations comparable with others4 ,with all the advantages of this barometer1 however1 it has recently been superseded1 to some extent1 because it was found to require more care than could ordinarily be expected to be given to it by the commander of a ship4 ,seamen do not exactly understand the value of such nice accuracy as the thousandth part of an inch1 but prefer an instrument that reads only to a hundredth part4 #bb4 ,,the ,,fitzroy ,,marine ,,barometer4 ,admiral ,fitz,roy deemed it desirable to construct a form of barometer as practically useful as possible for marine purposes4 ,one that should be less delicate in structure than the ,kew barometer1 and not so finely graduated4 ,one that could be set at a glance and read easily2 that would be more likely to bear the common shocks unavoidable in a ship of war4 ,accordingly1 the ,admiral has devised a barometer1 which he has thus described3-- ,this marine barometer1 for ,her ,majesty's service1 is adapted to general purposes4 ,it differs from barometers hitherto made in points of detail1 rather than principle3--#a4 ,the glass tube is packed with vulcanised india-rubber1 which checks vibration from concussion2 but does not hold it rigidly1 or prevent expansion4 #b4 ,it does not oscillate 7or pump71 though extremely sensitive4 #c4 ,the scale is porcelain1 very legible1 and not liable to change4 #d4 ,there is no iron anywhere 7to rust74 #e4 ,every part can be unscrewed1 examined1 or cleaned1 by any careful person4 #f4 ,there is a spare tube1 fixed in a cistern1 filled with boiled mercury1 and marked for adjustment in this1 or any similar instrument4 ,these barometers are graduated to hundredths1 and they will be found accurate to that degree1 namely the second decimal of an inch4 ,they are packed with vulcanised caoutchouc1 in order that 7by this1 and by a peculiar strength of glass tube7 guns may be fired near these instruments without causing injury to them by ordinary concussion4 ,it is hoped that all such instruments1 for the public service at sea1 will be quite similar1 so that any spare tube will fit any barometer4 ,to ,shift a ,tube4--,incline the barometer slowly1 and then take it down1 after allowing the mercury to fill the upper part4 ,lay the instrument on a table1 unscrew the outer cap at the joining just below the cistern swell1 then unscrew the tube and cistern1 by turning the cistern gently1 against the sun1 or to the left1 and draw out the tube very carefully without bending it in the least1 turning it a little1 if required1 as moved4 ,then insert the new tube very cautiously1 screw in1 and adjust to the diamond-cut mark for #bg inches4 ,attach the cap1 and suspend the barometer for use4 ,if the mercury does not immediately quit the top of the tube1 tap the cistern end rather sharply4 ,in a well-boiled tube1 with a good vacuum1 the mercury hangs1 at times1 so adhesively as to deceive1 by causing a supposition of some defect4 ,in about ten minutes the mercurial column should be nearly right2 but as local temperature affects the brass1 as well as the mercury1 slowly and unequally1 it may be well to defer any exact comparisons with other instruments for some few hours4 ,messrs4 ,negretti and ,zambra are the makers of these barometers for the ,royal ,navy4 ,fig4 #af is an illustration4 ,illustration3 ,fig4 #af4 ,the tube is fixed to a boxwood cistern1 which is plugged with very porous cane at the top1 to allow of the ready influence of a variation in atmospheric pressure upon the mercury4 ,round the neck of the cistern is formed a brass ring1 with a screw thread on its circumference4 ,this screws into the frame1 and a mark on the tube is to be adjusted to #bg inches on the scale1 the cistern covering screwed on1 and the instrument is ready to suspend4 ,the frame and all the fittings are brass1 without any iron whatever2 because the contact of the two metals produces a galvanic action1 which is objectionable4 ,the spare tube is fitted with india-rubber1 and ready at any time to replace the one in the frame4 ,the ease with which a tube can be replaced when broken is an excellent feature of the instrument4 ,the spare tube is carefully stowed in a box1 which can also receive the complete instrument when not in use4 ,all the parts are made to a definite gauge2 the frames are1 therefore1 all as nearly as possible similar to each other1 and the tubes--like rifle bullets--are adjustible to any frame4 ,if1 then1 the tube in use gets broken1 the captain can replace it by the other2 but1 as it is securely packed with india-rubber1 there is very little liability of its being broken by fair usage4 ,every person who knows the importance of the barometer on board ship1 will acknowledge that the supplementary tube is a decided improvement4 ,many instruments of this description are afloat in the ,royal ,navy1 and in a short time it may be expected that all the frames and tubes of barometers in the public service at sea will be similar in size and character2 so that should a captain have the misfortune to get both his tubes broken1 he would be able to borrow another from any ship he fell in with that had one to spare1 which would be perfectly accurate1 because it would have been verified before it was sent out4 #bc4 ,admiral ,fitz,roy's ,words for the ,scale4--,the graduation of inches and decimals are placed in this barometer on the right-hand side of the tube2 and on a similar piece of porcelain1 on the left-hand1 are engraved1 as legibly as they are expressed succinctly1 the following words1 of universal application in the interpretation of the barometer movements3-- ,,rise ,,fall ,,for ,,for ,,cold ,,warm ,,dry ,,wet ,,or ,,or ,,less ,,more ,,wind4 ,,wind4 -------- -------- ,,except ,,except ,,wet ,,from ,,wet ,,from ,,cooler ,,side4 ,,cooler ,,side4 ,reverting to the explanation of the words on the ,coast barometers 7at page #ad71 and comparing and considering them as given for northern latitudes1 and as they must be altered for southern latitudes1 it will be perceived1 that for all cold winds the barometer rises2 and falls for warm winds4 ,the mercury also falls for increased strength of wind2 and rises as the wind lulls4 ,likewise before or with rain the column of mercury falls2 but it rises with fine dry weather4 ,putting these facts together1 and substituting for the points of the compass the terms cold and warm1 the appropriateness of the words on the scale of this barometer is readily perceived4 ,these concise and practical indications of the movements in the barometer are applicable for instruments intended for use in any region of the world1 and are in perfect accordance with the laws of winds and weather deduced by ,dove and other meteorologists4 ,there is nothing objectionable in them1 and being founded upon experience and the deductions made from numerous recorded observations of the weather in all parts of the world1 as well as confirmed by the theories of science1 they may consequently be considered as generally reliable4 ,they involve no conjecture1 but express succinctly scientific principles4 #bd4 ,trials of the ,fitz,roy ,marine ,barometer under ,fire of ,guns4--,some of the first barometers made by ,messrs4 ,negretti and ,zambra on ,admiral ,fitz,roy's principle were severely tried under the heaviest naval gun firing1 on board ,h4,m4,s4 ,excellent2 and under all the circumstances1 they withstood the concussion4 ,the purpose of the trials was to ascertain whether the vulcanized india-rubber packing round the glass tube of a new marine barometer did check the vibration caused by firing1 and whether guns might be fired close to these instruments without causing injury to them4 ,in the first and second series of experiments1 a marine barometer on ,admiral ,fitz,roy's plan was tried against a marine barometer on the ,kew principle1 both instruments being new1 and treated in all respects similarly4 ,they were hung over the gun1 under the gun1 and by the side of the gun1 the latter both inside and outside a bulkhead1--in fact1 in all ways that they would be tried in action with the bulkheads cleared away4 ,the result was that the ,kew barometer was broken and rendered useless1 while the new pattern barometer was not injured in the least4 ,in a third series of experiments1 ,mr4 ,negretti being present1 five of the new pattern barometers were subjected to the concussion produced by firing a #fh-pounder gun with shot1 and #af lbs4 charge of powder4 ,they were suspended from a beam immediately under the gun1 then from a beam immediately over the gun1 and finally they were suspended by the arm to a bulkhead1 at a distance of only #c ft4 #f in4 from the axis of the gun2 and the result was1 according to the official report1 that all these barometers1 however suspended1 would stand1 without the slightest injury1 the most severe concussion that they would ever be likely to experience in any sea-going man-of-war4 ,these trials were conducted under the superintendence of ,captain ,hewlett1 ,c4,b41 and the guns were fired in the course of his usual instructions4 ,his reports to ,admiral ,fitz,roy1 giving all the particulars of the trials1 are published in the ,ninth ,number of ,meteorological ,papers1 issued by the ,board of ,trade4#b #be4 ,,negretti ,,and ,,zambra',s ,,farmer',s ,,barometer ,,and ,,domestic ,,weather-,,glass4 ,it is a well-known fact that the barometer is as much1 or even more affected by a change of wind as it is by rain2 and the objection raised against a simple barometer reading1 as leaving the observer in doubt whether to expect wind or rain1 is removed by the addition of the ,hygrometer1 an instrument indicating the comparative degree of dryness or dampness of the air2--a most important item in the determination of the coming weather4 ,the farmer should not be content to let his crops lie at the mercy1 so to speak1 of the weather1 when he has within his command instruments which may be the means of preventing damage to1 and in cases total loss of1 his crops4 ,the farmer hitherto has had to depend for his prognostication of the weather on his own unassisted ,weather ,wisdom2 and it is perfectly marvellous how expert he has become in its use4 ,science now steps in1 not to ignore this experience1 but on the contrary1 to give it most valuable assistance by extending it1 and enabling it to predict1 with an accuracy hitherto unknown1 the various changes that take place in this most variable of climates4 ,to the invalid1 the importance of predicting with tolerable accuracy the changes that are likely to occur in the weather1 cannot be over-rated4 ,many colds would be prevented1 if we could know that the morning so balmy and bright1 would subside into a cold and cheerless afternoon4 ,even to the robust1 much inconvenience may be prevented by a due respect to the indications of the hygrometer and the barometer1 and the delicate in health will do well to regard its warnings4 ,illustration3 ,fig4 #ag4 ,description of the ,instrument4--,the farmer's barometer1 as figured in the margin1 consists of an upright tube of mercury inverted in a cistern of the same fluid2 this is secured against a strong frame of wood1 at the upper end of which is fixed the scale1 divided into inches and tenths of an inch4 ,on either side of the barometer1 or centre tube1 are two thermometers--that on the left hand has its bulb uncovered and freely exposed1 and indicates the temperature of the air at the place of observation2 that on the right hand has its bulb covered with a piece of muslin1 from which depend a few threads of soft lamp cotton2 this cotton is immersed in the small cup situated just under the thermometer1 this vessel being full of water2 the water rises by capillary attraction to the muslin-covered bulb1 and keeps it in a constantly moist state4 ,these two thermometers1 which we distinguish by the names ,wet ,bulb and ,dry ,bulb1 form the ,hygrometer2 and it is by the simultaneous reading of these two thermometers1 and noting the difference that exists between their indications1 that the humidity in the atmosphere is determined4 ,admiral ,fitz,roy's words 7see p4 #bb7 are placed upon the scale of the barometer1 as the value of a reading depends1 not so much on the actual height of the mercury in the tube1 as it does on whether the column is rising1 steady1 or falling4 ,the moveable screw at the bottom of the cistern is for the purpose of forcing the mercury to the top of the tube when the instrument is being carried from place to place1 and it must always be unscrewed to its utmost limit when the barometer is hung in its proper place4 ,after this it should never be touched4 ,the manner in which the ,hygrometer acts is as follows3 ,it is a pretty well-known fact that water or wine is often cooled by a wet cloth being tied round the bottle1 and then being placed in a current of air4 ,the evaporation that takes place in the progressive drying of the cloth causes the temperature to fall considerably below that of the surrounding atmosphere1 and the contents of the bottle are thus cooled4 ,in the same manner1 then1 the covered wet bulb thermometer will be found invariably to read lower than the uncovered one2 and the greater the dryness of the air1 the greater will be the difference between the indications of the two thermometers2 and the more moisture that exists in the air1 the more nearly they will read alike4 ,the cup must be kept filled with pure water1 and occasionally cleaned out1 to remove any dirt4 ,the muslin1 or cotton-wick1 should also be renewed every few weeks4 ,the hygrometer may be had separate from the barometer1 if the combined instruments cannot be sufficiently exposed to the external air1 this being essential for the successful use of the hygrometer4 ,this farmer's weather-glass1 then1 consists of three distinct instruments3 the barometer1 the thermometer1 and the hygrometer4 ,he has thus at command the three instrumental data necessary for the prediction of the weather4 ,and now to describe-- ,how to ,use the ,instrument4--,the observations should be taken twice a day1 say at #i ,a4,m4 and #c ,p4,m42 and should be entered on a slip of paper1 or a slate hung up by the barometer4 ,the observer will then be able to see the different values of the readings from time to time1 and to draw his conclusions therefrom4 ,the thermometer on the left hand should first be read1 and a note made of its indication1 which is the temperature of the air4 ,the wet bulb thermometer should now be read1 and also noted2 and the difference should be taken of these two readings4 ,next read the barometer by moving the small index at the side of the tube until it is on a level with the top of the mercury4 ,having noted the number of inches at which the column stands1 compare with the last observation1 and see immediately whether the barometer is rising1 steady1 or falling4 ,now1 having taken the observations as above1 we naturally ask the question1 ,what are we to predict from them8 ,and1 probably1 the best way of answering this query will be by giving an example4 ,we will suppose that our readings yesterday were as follows3--,temperature1 #gj deg42 ,wet ,bulb1 #fi deg42 ,difference1 #a deg42 very moist air4 ,barometer1 #bi4e1 and that rain has fallen4 ,to-day1 we read3--,temperature1 #fj deg42 ,wet ,bulb1 #ee deg42 ,difference1 #e deg42 dryer air4 ,barometer1 #cj4 ,we may safely predict that the rain will cease1 and probably we may have wind from the northward4 ,in spring or autumn1 if the barometric height be steady any where between #bi4e and #cj inches1 with the temperature about #fj deg41 fresh to moderate south-westerly winds1 with cloudy sky1 will probably characterize the weather2 the indications of the hygrometer being then specially serviceable in enabling us to foretell rain2 but if the mercury become steady at about #cj4e inches1 with temperature about #dj deg41 north-easterly winds1 dry air1 and clear sky1 may be confidently expected4 ,many cases will doubtless suggest themselves to the observer where these figures do not occur1 and where he might find a difficulty in interpreting the indications of his instruments4 ,we have1 therefore1 drawn up some concise rules for his guidance2 and although they will not prove absolutely infallible guides to this acknowledged most difficult problem1 still1 they will be found of much service in foretelling the weather1 when added to an intelligent observation of ordinary atmospheric phenomena1 as force and direction of wind1 nature of any particular season1 and the time of year4 #bf4 ,,rules ,,for ,,foretelling ,,the ,,weather4 ,a ,,rising ,,barometer4 ,a ,rapid rise indicates unsettled weather4 ,a ,gradual rise indicates settled weather4 ,a ,rise1 with dry air1 and cold increasing in summer1 indicates wind from northward2 and if rain has fallen1 better weather is to be expected4 ,a ,rise1 with moist air and a low temperature1 indicates wind and rain from northward4 ,a ,rise1 with southerly wind1 indicates fine weather4 ,a ,,steady ,,barometer1 ,with dry air and a seasonable temperature1 indicates a continuance of very fine weather4 ,a ,,falling ,,barometer4 ,a ,rapid fall indicates stormy weather4 ,a ,rapid fall1 with westerly wind1 indicates stormy weather from northward4 ,a ,fall1 with a northerly wind1 indicates storm1 with rain and hail in summer1 and snow in winter4 ,a ,fall1 with increased moisture in the air1 and the heat increasing1 indicates wind and rain from southward4 ,a ,fall1 with dry air1 and cold increasing 7in winter71 indicates snow4 ,a ,fall1 after very calm and warm weather1 indicates rain with squally weather4 #bg4 ,causes which may bring about a ,fall or a ,rise in the ,barometer4#c--;,as heat produces rarefaction1 a sudden rise of temperature in a distant quarter may affect the weight of the atmosphere over our heads1 by producing an aerial current outwards1 to supply the place of the lighter air which has moved from its former position2 in which case the barometer will fall4 ,now such a movement in the atmosphere is likely to bring about an intermixture of currents of air of different temperatures1 and from this intermixture rain is likely to result4 ,on the other hand1 as cold produces condensation1 any sudden fall of temperature causes the column of air over the locality to contract and sink to a lower level1 whilst other air rushes in from above to supply the void2 and1 accordingly1 the barometer rises4 ,should this air1 as often happens1 proceed from the north1 it will contain in general but little moisture2 and hence1 on reaching a warmer latitude1 will take up the vapour of the air1 so that dry weather will result4 ,it is generally observed1 that wind causes a fall in the instrument2 and1 indeed1 in those greater movements of the atmosphere which we denominate storms or hurricanes1 the depression is so considerable as to forewarn the navigator of his impending danger4 ,it is evident1 that a draught of air in any direction must diminish the weight of the column overhead1 and consequently cause the mercury in the barometer to sink4 ,the connection1 therefore1 of a sinking of the barometric column with rain is frequently owing to the wind causing an intermixture of the aerial currents which1 by their motion1 diminish the weight of the atmosphere over our heads2 whilst a steady rise in the column indicates the absence of any great atmospheric changes in the neighbourhood1 and a general exemption from those causes which are apt to bring about a precipitation of vapour4 #bh4 ,use of the ,barometer in the management of ,mines4--,the inflammable and suffocating gases1 known to coal-miners as fire-damp and choke-damp1 are specifically heavier than air2 and as they issue from the fissures of the mine1 or are released from the coal1 the atmospheric pressure tends to drive them into the lowest and least ventilated galleries4 ,consequently a greatly reduced atmospheric pressure will favour a sudden outflow or advance of gas2 whence may result cases of explosion or suffocation4 ,it has been found that these accidents occur for the most part about the time of a low barometric column4 ,a reliable barometer should1 therefore1 be systematically consulted by those entrusted with the management or control of coal-mines1 so that greater vigilance and caution may be enjoined on the miners whenever the mercury falls low1 especially after it has been unusually high for some days4 #bi4 ,use of the ,barometer in estimating the ,height of ,tides4--,the pressure of the atmosphere affects the height of the tide1 the water being in general higher as the barometer is lower4 ,the expressions of seamen1 that frost nips the tide1 and fog nips the tide1 are explained by the high barometer which usually accompanies frost and fog4 ,m4 ,daussy1 ,sir ,j4 ,c4 ,ross1 and others1 have established that a rise of one inch in the barometer will have a corresponding fall in the tide of about one foot4 ,therefore navigators and pilots will appreciate the following suggestion of ,admiral ,fitz,roy3-- ,vessels sometimes enter docks1 or even harbours1 where they have scarcely a foot of water more than their draught2 and as docking1 as well as launching large ships1 requires a close calculation of height of water1 the state of the barometer becomes of additional importance on such occasions4 ,,chapter ,,ii4 ,,syphon ,,tube ,,barometers4 #cj4 ,principle of4--,if some mercury1 or any other fluid1 be poured into a tube of glass1 bent in the form of ,u1 and open at both ends1 it will rise to the same height in both limbs1 the tube being held vertically4 ,if mercury be poured in first1 and then water upon it at one end1 these liquids will not come to the same level2 the water will stand much higher than the mercury4 ,if the height of the mercury1 above the line of meeting of the fluids1 be one inch1 that of the water will be about thirteen-and-a-half inches4 ,the explanation of this is1 that the two columns balance each other4 ,the pressure of the atmosphere in each limb is precisely similar2 but the one column stands so much higher than the other1 because the fluid of which it is composed is so much lighter1 bulk for bulk1 than the other4 ,if one end of the tube be hermetically closed1 the other limb be cut off within a few inches of the bend1 and the tube carefully filled with mercury2 by placing it in a vertical position1 the mercury will fall1 if the closed limb be long enough1 until it is about thirty inches higher than that in the exposed limb1 where it will remain4 ,here the atmosphere presses upon the short column2 but not upon the long one4 ,it is this pressure1 therefore1 which maintains the difference of level4 ,in fact1 it forms a barometer without a cistern1 the short limb answering the purpose of a cistern4 ,the first barometers on this principle were devised by the celebrated philosopher1 ,dr4 ,hook1 as described in the next section4 #ca4 ,,dial1 ,,or ,,wheel ,,barometers4 ,the familiar household ,weather ,glasses are barometers on the syphon principle4 ,the portions of the two limbs through which the mercury will rise and fall with the varying pressure of the atmosphere are made of precisely the same diameter2 while the part between them is contracted4 ,on the mercury1 in the exposed limb1 rests a round float of ivory or glass2 to this a string is attached and passed over and around a brass pulley1 the other end carrying another lighter weight4 ,the weight resting on the mercury rises and falls with it4 ,on the spindle of the pulley1 which passes through the frame and centre of the dial-plate1 is fixed a light steel hand1 which revolves as the pulley turns round4 ,when the mercury falls for a decrease of atmospheric pressure1 it rises by the same quantity in the short tube1 and pushes up the float1 the counterpoise falls1 and thus moves the hand or pointer to the left4 ,when the pressure increases1 the pointer is drawn in a similar manner to the right4 ,illustration3 ,fig4 #ah4 ,illustration3 ,fig4 #ai4 ,illustration3 ,fig4 #bj4 ,the dials are generally made of metal silvered over or enamelled1 but porcelain may be used4 ,if the circumference of the pulley1 or wheel1 be two inches1 it will revolve once for an alteration of level amounting to two inches in each tube1 or four inches in the height of the barometric column2 and as the dial may be from twenty to thirty-six inches in circumference1 five to nine inches on the graduated scale corresponds to one inch of the column2 and hence the sub-divisions are distinctly perceptible1 and a vernier is not necessary4 ,the motion of the pointer alone is visible2 and a mahogany1 or rosewood1 frame1 supports1 covers1 and renders the instrument ornamental and portable4 ,in the back of the frame is a hinged door1 which covers the cavity containing the tube and fixtures4 ,the dial is covered by a glass in a brass rim1 similar to a clock face4 ,a brass index1 working over the dial1 moveable by a key or button1 may be applied1 and will serve to register the position of the hand when last observed4 ,these instruments are usually fitted with a thermometer1 and a spirit level2 the latter for the purpose of getting the instrument perfectly vertical4 ,they sometimes have1 in addition1 a hygrometer1 a sympiesometer1 an aneroid1 a mirror1 or a clock1 c41 singly or combined4 ,the frame admits of much variety of style and decoration4 ,it may be carved or inlaid4 ,the usual adjustment of scale is suited for localities at no considerable elevation above the sea4 ,accordingly1 being commercial articles1 they have been found frequently quite out of place4 ,when intended for use at high elevations1 they should have a special adjustment of scale4 ,as household instruments they are serviceable1 and ornamental4 ,but the supply-and-demand principle upon which they are sold1 has entailed upon those issued by inferior makers a generally bad adjustment of scale4 ,the illustrations are those of ordinary designs4 ,illustration3 ,fig4 #ba4 ,illustration3 ,fig4 #bb4 ,illustration3 ,fig4 #bc4 ,dial barometers required for transmission to distant parts1 as ,india and the ,colonies1 are furnished with a steel stop-cock1 to render them portable more effectually than can be done by the method of plugging the tube4 #cb4 ,,standard ,,syphon ,,barometer4 ,fig4 #bd represents the most accurate form of the ,gay ,lussac barometer4 ,the short limb is closed at the top1 after the mercury is introduced1 and a small lateral puncture is made at a1 which is covered over with a substance which permits the access of air1 but prevents the escape of any mercury when the instrument is packed for travelling4 ,the bent part of the tube is contracted to a capillary bore2 and just above this1 in the long limb1 is placed the air-trap1 already described 7see p4 #ag71 and here illustrated 7fig4 #be74 ,when reversed1 as it must be for portability1 the capillary attraction keeps the mercury in the long branch4 ,should the mercury of the short column get detached1 some small quantity of air may pass2 but it will be arrested at the pipette1 and will not vitiate the length of the barometric column4 ,it can be easily expelled by gently shaking or tapping the instrument before suspending it for observation4 ,in the illustration1 the zero of the scale is placed at ,z1 near the middle of the tube2 and the graduations extend above and below4 ,in making an observation1 it is necessary to take the reading ,,za on the long branch1 and ,,zb on the short one4 ,the sum of the two gives the height of the barometer4 ,the zero of the scale in some instruments is placed low down1 so as to require the difference of the two readings to be taken4 ,a thermometer is attached to the frame as usual4 ,illustration3 ,fig4 #bd4 ,illustration3 ,fig4 #be4 ,these instruments can be very accurately graduated1 and are very exact in their indications1 provided great care has been exercised in selecting the tubes1 which must be of the same calibre throughout the parts destined to measure the variations of atmospheric pressure4 ,they should be suspended so as to insure their hanging vertically4 ,the syphon barometer does not require correction for capillarity nor for capacity1 as each surface of the mercury is equally depressed by capillary attraction1 and the quantity of mercury which falls from the long limb of the tube occupies the same length in the short one4 ,the barometric height must1 however1 be corrected for temperature1 as in the cistern barometer4 ,tables containing the temperature corrections to be applied to barometer readings for scales engraved on the glass tube1 or on brass or wood frames1 are published4 ,,chapter ,,iii4 ,,barographs1 ,,or ,,self-,,registering ,,barometers4 #cc4 ,milne's ,self-,registering ,barometer4--,for a long time a good and accurate self-recording barometer was much desired4 ,this want is now satisfactorily supplied1 not by one1 but by several descriptions of apparatus4 ,the one first to be described was the design of ,admiral ,sir ,a4 ,milne1 who himself constructed1 in #aheg1 we believe1 the original instrument1 which he used with much success4 ,since that time several of these instruments have been made1 and have performed satisfactorily4 ,the barometer tube is a syphon of large calibre1 provided with a ,gay ,lussac pipette1 or air-trap2 and fitted with a float1 a wheel1 and a pointer1 as in the ,dial barometer4 ,the float is attached to a delicate watch-chain1 which passes over the wheel and is adequately counterpoised4 ,behind the indicating extremity of the pointer or hand is a projecting point1 which faces the frame of the instrument1 and is just within contact with the registering paper4 ,a clock is applied1 and fitted with auxiliary mechanism1 so as to be able to move the mounted paper with regularity behind the pointer1 and at designed equal intervals of time to release a system of levers and springs1 so as to cause the marker to impress a dot on the paper1 either by puncture or pencil-mark4 ,the paper is ruled with horizontal lines for the range of the mercurial column1 and parallel arcs of circles for the hours4 ,thus the barometer is rendered self-recording1 by night or day1 for a week or more2 hence the great value of the instrument4 ,the clock1 index1 and registering mechanism are protected from dust and interference by a glass front1 hinged on and locked4 ,as the temperature of the mercury is not registered1 there is fixed to the frame a ,sixe's thermometer to record the maximum and minimum temperatures1 which should be noted at least every twenty-four hours4 ,admiral ,fitz,roy has suggested the name ,atmoscope for ,admiral ,milne's barometer2 and he has also termed it a ,barograph4 ,this latter word appears to be applicable to all kinds of self-registering barometers hitherto designed4 ,of the arrangement under consideration ,admiral ,fitz,roy writes3--,it shows the alterations in tension1 or the pulsations1 so to speak1 of atmosphere1 on a large scale1 by hourly marks2 and the diagram expresses1 to a practised observer1 what the 'indicator card' of a steam-cylinder shows to a skilful engineer1 or a stethescope to a physician4 ,illustration3 ,fig4 #bf4 #cd4 ,modification of ,milne's ,barometer4--,the great difficulty to be overcome in ,milne's barometer1 is to adjust the mechanism for obtaining registration so that the action of the striker upon the pointer should not in the slightest degree move it from its true position4 ,a different mode of registration1 capable of recording accurately the least appreciable movement of the mercurial column1 has been effected4 ,in this instrument the registering paper is carried upon a cylinder or drum4 ,by reference to the illustration1 ,fig4 #bf1 the details of construction will be readily understood4 ,it should1 however1 be mentioned1 that it is not a picture of the outward appearance of the instrument4 ,the position of the barometer should be behind the clock2 it is represented on one side merely for the purpose of clearly illustrating the arrangement and principles4 ,the instrument has a large syphon barometer tube1 in which the mercurial column is represented4 ,on the mercury at ,a1 in its open end1 rests a glass float1 attached to a watch-chain1 or suitable silken cord1 the other end of which is connected to the top of the arched head on the short arm of a lever-beam4 ,the long arm of the beam is twice the length of the short arm1 for the following reason4 ,as the mercury falls in the long limb1 it rises through an equal space in the short limb of the tube1 and vice versa4 ,but the barometric column is the difference of height of the mercury in the two limbs2 hence the rise or fall of the float through half-an-inch will correspond to a decrease or an increase of the barometric column of one inch4 ,in order1 then1 to record the movements of the barometric column1 and not those of the float1 the arm of the beam connected with the float is only half the radius of the other arm4 ,both arms of the beam carry circular-arched heads1 which are similar portions of the complete circles1 the centre of curvature being the fulcrum1 or axis4 ,this contrivance maintains the leverage on each extremity of the beam always at the same distance from the fulcrum4 ,from the top of the large arched head a piece of watch-chain descends1 and is attached to the marker1 ,b1 which properly counterpoises the float1 ,a1 and is capable of easy movement along a groove in a brass bar1 so as to indicate the barometric height on an ivory scale1 ,c1 fixed on the same vertical framing4 ,on the opposite side of the marker1 ,b1 is formed a metallic point1 which faces the registration sheet and is nearly in contact with it4 ,the framing1 which carries the scale and marker1 is an arrangement of brass bars1 delicately adjusted and controlled by springs1 so as to permit of a quick horizontal motion1 in a small arc1 being communicated to it by the action of the hammer1 ,e1 of the clock1 whereby the point of the marker is caused to impress a dot upon the paper4 ,the same clock gives rotation to the hollow wooden cylinder1 ,d1 upon which is mounted the registering paper4 ,the clock must be rewound when a fresh paper is attached to the cylinder1 which may be daily1 weekly1 or monthly1 according to construction2 and the series of dots impressed upon the paper shows the height of the barometric column every hour by day and night4 ,the space traversed by the marker is precisely equal to the range of the barometric column4 #ce4 ,king's ,self-,registering ,barometer4--,mr4 ,alfred ,king1 ,engineer of the ,liverpool ,gas-light ,company1 designed1 so long ago as #ahed1 a barometer to register1 by a continuous pencil-tracing1 the variations in the weight of the atmosphere2 and a highly-satisfactory self-recording barometer1 on his principle and constructed under his immediate superintendence1 has quite recently been erected at the ,liverpool ,observatory4 ,illustration3 ,fig4 #bg4 ,fig4 #bg is the front elevation of this instrument4 ,a1 the barometer tube1 is three inches in internal diameter1 and it floats freely 7not being fixed as usual7 in the fixed cistern1 ,b1 guided by friction-wheels1 ,w4 ,the top end of the tube is fastened to a peculiar chain1 which passes over a grooved wheel turning on finely-adjusted friction rollers4 ,the other end of the chain supports the frame1 ,d1 which carries the tracing pencil4 ,the frame is suitably weighted and guided1 and faces the cylinder1 ,c1 around which the tracing paper is wrapped1 and which rotates once in twenty-four hours by the movement of a clock4 ,mr4 ,hartnup1 ,director of the ,liverpool ,observatory1 in his ,annual ,report1 #ahfh1 says3--,for one inch change in the mercurial column the pencil is moved through five inches1 so that the horizontal lines on the tracing1 which are half an inch apart1 represent one-tenth of an inch change in the barometer4 ,the vertical lines are hour lines1 and being nearly three-quarters of an inch apart1 it will be seen that the smallest appreciable change in the barometer1 and the time of its occurrence1 are recorded4 ,it has been remarked by persons in the habit of reading barometers with large tubes1 that1 in squally weather1 sudden and frequent oscillations of the mercurial column are sometimes seen4 ,now1 to register these small oscillations must be a very delicate test of the sensitiveness of a self-registering barometer1 as the time occupied by the rise and fall of the mercury in the tube in some cases does not exceed one minute4 ,mr4 ,hartnup affirms that the tracing of this instrument exhibits such oscillations whenever the wind blows strong and in squalls4 ,as the barometer in this instrument is precisely similar to the ,long ,range ,barometer invented by ,mr4 ,mc,neild 7and which will be found described at page #dh71 it may be desirable to quote the following1 from ,mr4 ,hartnup's ,report3--,mr4 ,king constructed a small model instrument to illustrate the principle4 ,this instrument was entrusted to my care for examination1 and it was exhibited to the scientific gentlemen who visited the ,observatory in #ahed1 during the meeting of the ,british ,association for the ,advancement of ,science4 #cf4 ,syphon1 with ,photographic ,registration4--,a continuous self-registering barometer has been constructed1 in which photography is employed4 ,those who may wish to adopt a similar apparatus1 or thoroughly to understand the arrangements and mode of observation1 should consult the detailed description given in the ,greenwich ,magnetical and ,meteorological ,observations1 #ahdg4 ,as the principles are applicable to photographic registration of magnetic and electric as well as meteorologic variations in instrumental indications1 it would be beside our purpose to describe fully the apparatus4 ,the barometer is a large syphon tube2 the bore of the upper and lower extremities1 through which the surfaces of the mercury rise and fall1 is #a-a_/aj inch in diameter4 ,the glass float in the open limb is attached to a wire1 which moves a delicately-supported light lever as it alters its elevation4 ,the fulcrum of the lever is on one side of the wire2 the extremity on the other side1 at four times this distance from the fulcrum1 carries a vertical plate of opaque mica1 having a small aperture4 ,through this hole the light of a gas-jet shines upon photographic paper wrapped round a cylinder placed vertically1 and moved round its axis by a clock fixed with its face horizontal4 ,the cylinder is delicately supported1 and revolves in friction rollers4 ,a bent wire on the axis is embraced by a prong on the hour hand of the time-piece2 therefore the cylinder is carried round once in twelve hours4 ,it might be arranged for a different period of rotation4 ,as the cylinder rotates1 the paper receives the action of the light1 and a photographic trace is left of the movements of the barometer four times the extent of the oscillations of the float1 or twice the length of the variations in the barometric column4 ,certain chemical processes are required in the preparation of the paper1 and in developing the trace4 ,the diagram which we give on the next page1 with the explanation1 taken from ,drew's ,practical ,meteorology1 will enable the above description to be better understood3 ,illustration3 ,fig4 #bh4 ,q e is a lever whose fulcrum is e1 the counterpoise f nearly supporting it2 s is an opaque plate of mica1 with a small aperture at p1 through which the light passes1 having before been refracted by a cylindrical lens into a long ray1 the portion only of which opposite the aperture p impinges on the paper2 d is a wire supported by a float on the surface of the mercury2 ,g ,h is the barometer2 p1 the vertical cylinder charged with photographic paper2 r1 the photographic trace2 ,i1 the timepiece1 carrying round the cylinder by the projecting arm t4 ,it is evident that the respective distances of the float and the aperture p from the fulcrum may be regulated so that the rise and fall of the float may be multiplied to any extent required4 ,when only the lower surface of the mercury in a syphon barometer is read1 as in the instrument just described1 a correction for temperature is strictly due to the height of the quicksilver in the short tube2 but this in so short a column will rarely be sensible4 ,,chapter ,,iv4 ,,mountain ,,barometers4 #cg4 ,the ,syphon ,tube ,mountain ,barometer1 on ,gay ,lussac's principle1 constructed as described at page #ca1 and fixed in a metallic tubular frame1 forms a simple and light travelling instrument4 ,the graduations are made upon the frame1 and it is suspended for reading by a ring at the top1 from beneath an iron tripod stand1 which is usually supplied with it4 ,considerable care is requisite in adjusting the verniers1 so as to keep the instrument steady and vertical4 ,a drawback to the convenience of this barometer is the movement of the mercury in the short limb1 which is generally not confined1 and hence has every facility for becoming quickly oxidised in travelling4 ,to remedy this1 ,messrs4 ,negretti and ,zambra so construct the ,mountain ,syphon ,barometer that by a simple half turn of a screw the mercury can be confined for portability1 while the lower limb can be taken out for cleaning whenever found requisite4 #ch4 ,mountain ,barometer on ,fortin's principle4--,this barometer1 with ,fortin's cistern1 as arranged by ,messrs4 ,negretti and ,zambra1 is an elegant1 manageable1 and very accurate instrument for travelling purposes1 and well adapted for careful measurement of heights4 ,the cistern is made large enough to receive all the mercury that will fall from the tube at the highest attainable elevation4 ,the screw at the bottom confines the mercury securely for carriage1 and serves to adjust the surface of the mercury to the zero of the scale when making an observation4 ,the vernier reads to 4#jjb of an inch1 and slides easily on the brass frame1 which is made as small in diameter as is compatible with the size of the tube4 ,the tube in this barometer should be altogether without contractions1 so that the mercury will readily fall when it is set up for observation4 ,it must be carefully calibrated1 and its internal diameter ascertained1 in order that correction may be made for capillarity4 ,this correction1 however1 should be combined with the error of graduation1 and form a permanent index error1 ascertainable at any time by comparison with an acknowledged standard barometer4 ,the barometer is supported in the tripod stand 7furnished as part of the instrument7 when used for observation4 ,it is suspended by placing two studs1 in the ring on the frame1 in slots formed on the top of the stand1 so that it hangs freely and vertically in gimbals4 ,to the metal top of the stand1 mahogany legs are hinged4 ,to make the barometer portable1 it must be lifted out of the stand1 sloped gently until the mercury reaches the top1 turning the screw at the bottom meanwhile2 then invert and screw until the mercury is made tight4 ,the inverted instrument packs in the stand1 the legs being formed to fit round the frame2 and receptacles are scooped out for the cistern1 thermometer1 gimbals1 and vernier2 so that the instrument is firmly surrounded by the wooden legs1 which are held fast together by brass rings passed over them4 ,illustration3 ,fig4 #bi4 #ci4 ,newman's ,mountain ,barometer4--,fig4 #bi is an illustration of the mountain barometer known as ,newman's4 ,the cistern consists of two separate compartments2--the top of the lower and the bottom of the upper1 being perfectly flat1 are pivoted closely together at the centres1 so that the lower can move through a small arc1 when turned by the hand4 ,this movement is limited by two stops4 ,the top of the lower compartment and the bottom of the upper have each a circular hole1 through which the mercury communicates4 ,when the instrument is required for observation1 the cistern is turned close up to the stop marked open or not portable4 ,when it is necessary to pack it for travelling1 the mercurial column must be allowed to fill the tube by sloping the barometer gently2 then invert it1 and move the cistern to the stop marked shut or portable4 ,in this condition1 the upper compartment is completely filled with mercury1 and consequently that in the tube cannot move about1 so as to admit air or endanger the tube4 ,nor can the mercury pass back to the lower compartment1 as the holes are not now coincident1 and the contact is made too perfect to allow the mercury to creep between the surfaces4 ,the tube does not enter the lower compartment1 which is completely full of mercury when the instrument is arranged for observation4 ,the spare capacity of the upper cistern is sufficient to receive the mercury which descends from the tube to the limit of the engraved scale1 which in these barometers generally extends only to about #bj inches4 ,a lower limit could of course be given by increasing the size of the cisterns1 which it is not advisable to do unless for a special purpose4 ,this barometer may be had mounted in wood1 or in brass frame4 ,if in wood1 it has a brass shield1 which slides round the scale part of the frame1 so as to be easily brought in front of the tube and scale as a protection in travelling2 the vernier screw1 in this case1 being placed at the top of the instrument4 ,when the scale is graduated with true inches1 the neutral point1 the capacity and capillarity corrections should be marked on the frame4 ,the graduated scales1 however1 placed on these barometers in brass frames1 are usually artificial inches1 like the ,kew plan of graduation2 the advantage being that one simple correction only is required1 viz4 one for index error and capillarity combined1 which can always be readily determined by comparison with a standard barometer2 moreover1 as no adjustment of cistern is required in reading1 the instrument can be verified by artificial pressure throughout the scale1 by the plan practised at ,kew1 ,liverpool1 c41 and already described 7see p4 #ah74 #dj4 ,,negretti ,,zambra',s ,,patent ,,mountain ,,and ,,other ,,barometers4 ,this invention is intended to make mountain and other barometers of standard accuracy stronger1 more portable1 and less liable to derangement1 when being carried about1 than heretofore1 by dispensing with the ordinary flexible cistern containing the mercury at the bottom of the instrument1 and adapting in lieu thereof a rigid cistern constructed of glass and iron4 ,the cistern is composed of a glass cylinder1 which is secured in a metallic tube or frame4 ,in order to render the cistern mercury-tight at top and bottom1 metal caps are screwed into the tube or frame1 and bear against leather washers placed between them and the edges of the glass cylinder4 ,the upper cap of the cistern is tapped with a fine threaded screw to receive the iron plug or socket1 into which the barometer tube is securely fixed4 ,the whole length of this plug has a fine screw cut upon it by which the cistern can be screwed up or down4 ,at the side of this plug or socket1 extending from the lower end to within half an inch of the top1 is cut a groove for admitting the air to the surface of the mercury within the cistern when the barometer is in use4 ,an ivory point is screwed into the under surface of the plug1 carrying the barometer tube4 ,this ivory point is very carefully adjusted by measurement to be the zero point of the instrument1 from which the barometer scale of inches is divided4 ,the surface of the mercury in the cistern is adjusted to the zero point by screwing the cistern up or down until the ivory point and its reflected image are in contact4 ,illustration3 ,fig4 #cj4 ,the instrument 7fig4 #cj7 is shown in a state of adjustment1 ready to take an observation2 but when it is desired to render it portable1 it must be inclined1 until mercury from the cistern fills the tube2 the cistern must then be screwed up on the socket1 so as to bring the face of the upper cap against the under side of the shoulder of the cover immediately above it2 the instrument may then be carried without being liable to derangement4 ,precautions necessary in using the ,mountain ,barometer4--,on removing the barometer from its case after a journey1 allow it to remain with its scale end downward1 whilst the cistern is unscrewed to the extent of one turn of the screw1 after which slightly shake the cistern2 the mercury in it will then completely fill the end of the barometer tube1 should any portion of it have escaped therefrom4 ,the barometer is then inverted1 and if it be desired to make an observation1 suspend it vertically from its stand by the ring at top4 ,the cistern must then be unscrewed1 until the surface of the mercury is brought just level with the extreme end of the ivory or zero point fixed to the iron plug on which the glass cistern moves up and down4 ,should the elevation of the place where the barometer is to be used be considerably above the sea level1 it will be well--after suspending it from the stand--to unscrew the cistern several turns1 holding the barometer in an oblique position1 as at great heights the mercury will fall considerably quicker than the cistern can be unscrewed1 thereby filling it to overflowing2 but by partly unscrewing the cistern first1 room is given for the reception of a fall of mercury to the extent of several inches4 ,the cistern must not be unscrewed when the ,instrument is ,,inverted more than two turns of the screw1 otherwise the mercury will flow out through the groove4 ,it is found safer when travelling to carry the barometer in a horizontal position1 or with its cistern end uppermost4 ,to clean the ,barometer4--,should at any time the mercury in the cistern become oxidised1 and reading from its surface be difficult1 it can be readily cleaned by removing the cistern and its contained mercury from the barometer frame by unscrewing it when in a horizontal position2 this precaution is necessary that the mercury in the tube may not escape1 and thereby allow air to enter4 ,the cistern must then be emptied1 and with a dry clean leather1 or silk handkerchief1 well cleaned4 ,the operation of cleaning being performed1 return the cistern to the frame1 and screw it until the face is brought up against the under side of the shoulder1 still keeping the instrument horizontal4 ,the cistern is now ready for re-filling1 to do which stand the barometer on end head downwards1 and remove the small screw at bottom2 through the aperture thus opened1 pour in mercury1 passing it through a paper funnel with a very small aperture4 ,it is well to pass the mercury through a very small funnel two or three times before returning it to the barometer cistern1 as by this process all particles of dust or oxide adhere to the paper1 and are effectually removed4 ,should any small quantity of the mercury be lost during the operation of cleaning1 it is of no importance so long as sufficient remains to allow of adjustment to the zero point4 ,this latter constitutes one of the great advantages of this new instrument over the ordinary barometer2 for1 in the majority of cases1 after an instrument has been compared carefully with a standard1 should mercury be lost1 there is no means of correcting the error unless a standard barometer be at hand2 the new barometer is1 in this respect1 independent1 a little mercury more or less being unimportant4 #da4 ,short ,tube ,barometer4--,this is simply a tube shorter1 as may be required1 than that necessary to show the atmospheric pressure at the sea level4 ,it is convenient for balloon purposes1 and for use at mountain stations1 being of course a special construction4 #db4 ,method of ,calculating ,heights by the ,barometer4--,the pressure of the atmosphere being measured by the barometer1 it is evident that as the instrument is carried up a high mountain or elevated in a balloon1 the length of the column must decrease as the atmospheric pressure decreases1 in consequence of a stratum of air being left below4 ,the pressure of air arises from its weight1 or the attraction of gravitation upon it1 and therefore the quantity of air below the barometer cistern cannot influence the height of the column4 ,hence it follows that a certain relation must exist between the difference of the barometric pressure at the foot and at the top of a hill or other elevation1 and the difference of the absolute heights above the sea4 ,theoretical investigation1 abundantly confirmed by practical results1 has determined that the strata of air decrease in density in a geometrical proportion1 while the elevations increase in an arithmetical one4 ,hence we have a method of determining differences of level1 by observations made on the density of the air by means of the barometer4 ,it is beyond our purpose to explain in detail the principles upon which this method is founded1 or to give its mathematical investigation4 ,we append ,tables1 which will be useful to practical persons1--surveyors1 engineers1 travellers1 tourists1 c41--who may carry a barometer as a travelling companion4 ,table ,i4 is calculated from the formula1 height in feet #fj1bjj 7log4 #bi4ibb - log4 ,b7 #ibe2 where #bi4ibb is the mean atmospheric pressure at #cb deg4 ,f41 and the mean sea-level in latitude #de deg42 and ,b is any other barometric pressure2 the #ibe being added to avoid minus signs in the ,table4 ,table ,,ii4 contains the correction necessary for the mean temperature of the stratum of air between the stations of observation2 and is computed from ,regnault's co-efficient for the expansion of air1 which is 4#jjbjcf of its volume at #cb deg4 for each degree above that temperature4 ,table ,,iii4 is the correction due to the difference of gravitation in any other latitude1 and is found from the formula1 x #a 4#jjbfe cos4 #b lat4 ,table ,,iv4 is to correct for the diminution of gravity in ascending from the sea-level4 ,to use these ,tables3 ,the barometer readings at the upper and lower stations having been corrected and reduced to temperature #cb deg4 ,f41 take out from ,table ,i4 the numbers opposite the corrected readings1 and subtract the lower from the upper4 ,multiply this difference successively by the factors found in ,tables ,,ii4 and ,,iii4 ,the factor from ,table ,,iii4 may be neglected unless precision is desired4 ,finally1 add the correction taken from ,table ,,iv4 ,,table ,i4 ,approximate ,height due to ,barometric ,pressure4 ---------------------------------------- ------ ,inches4 ,feet4,inches4 ,feet4,inches4 ,feet4 --------------------------------------- #ca4j #j #bh4b #bdge #be4d #ebji #cj4i #hd 4#a #befh 4#c #ecab 4#h #afi #bh4j #bffa 4#b #edae 4#g #bed #bg4i #bged 4#a #eeai 4#f #cci 4#h #bhdh #be4j #efbc 4#e #dbe 4#g #bidb #bd4i #egbh 4#d #eaa 4#f #cjcg 4#h #ehcc 4#c #eig 4#e #cacb 4#g #eici 4#b #fhc 4#d #cbbg 4#f #fjde 4#a #ggj 4#c #ccbc 4#e #faeb #cj4j #heg 4#b #cdai 4#d #fbei #bi4i #idd 4#a #ceae 4#c #fcff 4#h #ajcb #bg4j #cfab 4#b #fdgd 4#g #aabj #bf4i #cgji 4#a #fehb 4#f #abjh 4#h #chjf #bd4j #ffia 4#e #abif 4#g #cijd #bc4i #fhjj 4#d #ache 4#f #djjb 4#h #fiaj 4#c #adgd 4#e #dajj 4#g #gjbj 4#b #aefc 4#d #daii 4#f #gaca 4#a #afec 4#c #dbih 4#e #gbdb #bi4j #agdc 4#b #dcih 4#d #gcec #bh4i #ahcc 4#a #ddih 4#c #gdfe 4#h #aibd #bf4j #deih 4#b #gegg 4#g #bjae #be4i #dfii 4#a #gfij 4#f #bajf 4#h #dhjj #bc4j #ghjc 4#e #baih 4#g #dijb #bb4i #giag 4#d #bbij 4#f #ejjd 4#h #hjcb 4#c #bchb 4#e #eajf 4#g #hadg ---------------------------------------- ------ ,,table ,i4--continued4 ,approximate ,height due to ,barometric ,pressure4 ---------------------------------------- --------- ,inches4 ,feet4 ,inches4 ,feet4 ,inches4 ,feet4 ---------------------------------------- -- #bb4f #hbfb #ah4i #abicg #ae4b #ahfcb 4#e #hcgh 4#h #acjgf 4#a #ahhje 4#d #hdie 4#g #acbae #ae4j #ahigi 4#c #hfab 4#f #accee #ad4i #aiaed 4#b #hgbi 4#e #acdif 4#h #aiccj 4#a #hhdg 4#d #acfch 4#g #aiejg #bb4j #hiff 4#c #acghj 4#f #aifhe #ba4i #ijhe 4#b #acibc 4#e #aihfe 4#h #ibje 4#a #adjfg 4#d #bjjdf 4#g #icbe #ah4j #adbab 4#c #bjbbh 4#f #iddf #ag4i #adceh 4#b #bjdab 4#e #iefg 4#h #adeje 4#a #bjeig 4#d #ifhi 4#g #adfeb #ad4j #bjghc 4#c #ihaa 4#f #adhjj #ac4i #bjigj 4#b #iicd 4#e #adidi 4#h #baaei 4#a #ajjeh 4#d #aejii 4#g #bacdi #ba4j #ajahb 4#c #aebej 4#f #baeda #bj4i #ajcjg 4#b #aedjb 4#e #bagcd 4#h #ajdcb 4#a #aeeed 4#d #baibh 4#g #ajeeh #ag4j #aegjg 4#c #bbabd 4#f #ajfhd #af4i #aehfa 4#b #bbcba 4#e #ajhab 4#h #afjaf 4#a #bbebj 4#d #ajidj 4#g #afagb #ac4j #bbgbj 4#c #aajfi 4#f #afcbi #ab4i #bbibb 4#b #aaaih 4#e #afdhg 4#h #bcabf 4#a #aacbh 4#d #affdf 4#g #bccca #bj4j #aadeh 4#c #afhjf 4#f #bcech #ai4i #aaehi 4#b #afifg 4#e #bcgdf 4#h #aagba 4#a #agabi 4#d #bcief 4#g #aahec #af4j #agbib 4#c #bdafh 4#f #aaihf #ae4i #agdef 4#b #bdcha 4#e #ababj 4#h #agfba 4#a #bdeif 4#d #abbed 4#g #agghg #ab4j #bdhac 4#c #abchi 4#f #agied #aa4i #bejcb 4#b #abebe 4#e #ahabb 4#h #bebec 4#a #abffb 4#d #ahbia 4#g #bedgf #ai4j #abgii 4#c #ahdfa 4#f #begjj ---------------------------------------- --------- ,,table ,,ii4 ,correction due to ,mean ,temperature of the ,air4 ---------------------------------------- --- ,mean ,factor4,mean ,factor4,mean ,factor4 ,temp4 ,temp4 ,temp4 ------------------------------------ #aj deg4 #j4iee #ce deg4 #a4jjf #fj deg4 #a4jeg #aa 4#ieg #cf #a4jjh #fa #a4jei #ab 4#iei #cg #a4jaj #fb #a4jfa #ac 4#ifa #ch #a4jab #fc #a4jfc #ad 4#ifc #ci #a4jad #fd #a4jfe #ae 4#ife #dj #a4jaf #fe #a4jfg #af 4#ifg #da #a4jah #ff #a4jfi #ag 4#ifi #db #a4jbj #fg #a4jga #ah 4#iga #dc #a4jbb #fh #a4jgc #ai 4#igd #dd #a4jbd #fi #a4jge #bj 4#igf #de #a4jbf #gj #a4jgg #ba 4#igh #df #a4jbi #ga #a4jgi #bb 4#ihj #dg #a4jca #gb #a4jha #bc 4#ihb #dh #a4jcc #gc #a4jhc #bd 4#ihd #di #a4jce #gd #a4jhf #be 4#ihf #ej #a4jcg #ge #a4jhh #bf 4#ihh #ea #a4jci #gf #a4jij #bg 4#iij #eb #a4jda #gg #a4jib #bh 4#iib #ec #a4jdc #gh #a4jid #bi 4#iid #ed #a4jde #gi #a4jif #cj 4#iif #ee #a4jdg #hj #a4jih #ca #j4iih #ef #a4jdi #ha #a4ajj #cb #a4jjj #eg #a4jea #hb #a4ajb #cc #a4jjb #eh #a4jec #hc #a4ajd #cd #a4jjd #ei #a4jee #hd #a4ajf ---------------------------------------- --- ,,table ,,iii4 ---------------------------------------- --------------- ,latitude4,factor4,latitude4,factor4,lat itude4,factor4 ---------------------------------------- -------- #hj deg4 #j4iigea #ej #j4iiied #bj #a4jjbjc #ge #j4iiggj #de #a4jjjjj #ae #a4jjbcj #gj #j4iigig #dj #a4jjjdf #aj #a4jjbdi #fe #j4iihcj #ce #a4jjjij #e #a4jjbfa #fj #j4iihfh #cj #a4jjacb #j #a4jjbfe #ee #j4iiiaj #be #a4jjagj ---------------------------------------- --------------- ,,table ,,iv4 ---------------------------------------- ------------ ,height in ,correction ,height in ,correction ,thousand ,feet4 ,additive4,thousand ,feet4 ,additive4 ---------------------------------------- -------- #a #c #ad #dd #b #e #ae #dh #c #h #af #eb #d #aa #ag #ef #e #ad #ah #fj #f #ag #ai #fe #g #bj #bj #fi #h #bc #ba #gd #i #bf #bb #gh #aj #cj #bc #hc #aa #cc #bd #hh #ab #cg #be #ic #ac #da #bf #ih ---------------------------------------- ------------ ,,example #a4 ,on ,october #bast1 #aheb1 when ,mr4 ,welsh ascended in a balloon1 at #c;h4 #cjm4 p4m41 the barometer1 corrected and reduced1 was #ah4he1 the air temperature #bg deg41 while at ,greenwich1 #aei feet above the sea1 the barometer at the same time was #bi4ig inches1 air temperature #di deg41 the balloon not being more than #e miles ,s4,w4 from over ,greenwich2 required its elevation4 ,feet4 ,barometer in ,balloon #ah4he1 ,table ,i4 #acjjg at ,greenwich #bi4ig #hhc ----- #ababd ,mean ,temperature1 #ch deg41 ,table ,,ii4 ,factor #a4jab ----- #abbfi4 ----- ,latitude #ea-a_/b deg41 ,factor from ,table ,,iii4 4#iiida ----- #abbfb ,correction from ,table ,,iv4 #ch ----- #abcjj ,elevation of ,greenwich #aei ----- ,balloon #abdei feet4 ,the following examples1 from the balloon ascents of ,j4 ,glashier1 ,esq41 ,f4,r4,s41 will serve for practice4#d #b4 ,ascended from ,wolverhampton1 #ahth ,august1 #ahfb1 at #b;h4 #chm4 p4m42 barometer 7in all cases corrected and reduced to #cb deg4 ,f7 was #ad4hfh1 the temperature of the air #bf deg42 at the same time1 at ,wrottesley ,hall1 #eca feet above the sea1 in latitude #eb-a_/b deg4 ,n1 the barometer was #bi4df1 and the temperature of the air #fe deg4#d2 find the elevation of the balloon above the sea4 ,height1 #ah1iei feet4 #c4 ,from the same place an ascent was made #eth ,september1 #ahfb1 when at #a;h4 #dhm4 p4m4 barometer was #aa4ied1 air ,o deg42 at ,wrottesley ,hall #bi4ch1 air #ef deg4 ,height1 #bc1ibc feet4 #d4 ,from the ,crystal ,palace a balloon ascent was made #bjth ,august1 #ahfb4 ,at #f;h4 #dgm4 p4m4 barometer was #be4ee1 air #ej deg4#e2 and at the same time at ,greenwich ,observatory1 at #aei feet above the sea1 the barometer was #bi4ha1 air #fc deg4 ,height1 #d1djf feet4 #e4 ,from the same place an ascent was made #hth ,september1 #ahfb4 ,at #e p4m41 the balloon being over ,blackheath1 barometer was #be4fj1 and the air #di deg4#e1 while at ,greenwich1 barometer was #bi4ib1 air #ff deg4#d4 ,height1 #d1dfa feet4 ,,chapter ,v4 ,,secondary ,,barometers4 #dc4 ,desirability of ,magnifying the ,barometer ,range4--,the limits within which the ordinary barometric column oscillates1 do not exceed four inches for extreme range1 while the ordinary range is confined to about two inches2 hence it has often been felt that the public utility of the instrument would be greatly enhanced if by any means the scale indications could be increased in length4 ,this object was sought to be obtained by bending the upper part of the tube from the vertical1 so that the inches on the scale could be increased in length in proportion to the secant of the angle it made with the vertical4 ,this was called the diagonal barometer4 ,the upper part of the tube has also been formed into a spiral1 and the scale1 placed along it1 is thus greatly enlarged4 ,but these methods of enlarging the indications cannot be so successfully accomplished1 nor so cheaply nor so elegantly1 as is done by the principle employed in the dial barometer4 ,hence they are not in use4 ,illustration3 ,fig4 #ca4 #dd4 ,howson's ,long ,range ,barometer4--,very recently quite a novel design has been patented by ,mr4 ,howson1 for a long range barometer4 ,the construction requires neither distortion of the tube1 nor mechanism for converting a short scale into a long one2 but the mercury itself rises and falls1 through an extended range1 naturally1 and in simple obedience to the varying pressure of the atmosphere4 ,the tube is fixed1 but its cistern is sustained by the mere pressure of the atmosphere4 ,looking at the instrument1 it seems a perfect marvel4 ,it appears as though the cistern with the mercury in it must fall to the ground4 ,the bore of the tube is wide1 about an inch across4 ,a long glass rod is fixed to the bottom of the glass cistern1 where a piece of cork or some elastic substance is also placed4 ,the tube is filled with mercury2 the glass rod is plunged into the tube as it is held top downwards1 until the cork gets close up to the tube and fits tightly against it4 ,the pressure against the cork simply prevents the mercury from coming out while the instrument is being inverted4 ,when it is inverted1 the mercury partly falls1 and forms an ordinary barometric column4 ,when the top is held1 the cistern and glass rod1 instead of falling away1 remain perfectly suspended4 ,there is no material support to the cistern2 the tube only is fixed1 the cistern hangs to it4 ,glass is many times lighter than mercury4 ,when the glass rod is introduced1 it displaces an equal volume of mercury4 ,the glass rod1 being so much lighter than mercury1 floats and sustains the additional weight of the cistern by its buoyancy4 ,in the mean time1 the atmosphere is acting upon the mercury1 keeping up the ordinary barometric column4 ,supposing there is a rise in the ordinary barometer1 the atmosphere presses some more mercury up the tube4 ,this mercury is taken out of the cistern1 which of course becomes lighter1 and therefore the rod and cistern float up a little higher1 which thus causes the column of mercury to rise still more4 ,the increased pressure and buoyancy thus acting together1 increase the ascent in the barometric column1 as shown by the fixed scale4 ,one inch in the barometer might be represented by two or more inches in this instrument1 according to construction4 ,supposing there was a decrease of pressure1 the mercury would fall1 come into the cistern1 make it heavier1 and increase the fall somewhat4 ,friction guides1 at the top of the rod1 prevent it coming into contact with the side of the tube when vertically suspended4 ,the illustration1 ,fig4 #ca1 shows the appearance of the instrument as framed in wood by the makers1 ,messrs4 ,negretti and ,zambra4 #de4 ,mc,neild's ,long ,range ,barometer4--,a barometer designed by a gentleman named ,mc,neild is on a directly opposite principle to the one just described4 ,the tube is made to float on the mercury in the cistern4 ,it is filled with mercury1 inverted in the usual manner1 then allowed to float1 being held vertically by glass friction points or guides4 ,by this contrivance1 the ordinary range of the barometer is greatly increased4 ,one inch rise or fall in the standard barometer may be represented by four or five inches in this instrument1 so that it shows small variations in atmospheric pressure very distinctly4 ,as the mercury falls in the tube with a decrease of pressure1 the surface of the mercury in the cistern rises1 and the floating tube rises also1 which causes an additional descent in the column1 as shown by fixed graduations on the tube4 ,with an increase of pressure1 some mercury will leave the cistern and rise in the tube1 while the tube itself will fall1 and so cause an additional ascent of mercury4 ,this barometer is identical in principle with ,king's ,barograph 7see p4 #cd74 ,the construction of ,howson's and ,mc,neild's ,barometers has been assigned to ,messrs4 ,negretti and ,zambra4 ,these instruments are usually made for domestic purposes with a scale of from three to five1 and for public use from five to eight times the scale of the ordinary standard4 ,their sensitiveness is consequently increased in an equal proportion1 and they have the additional advantage of not being affected by differences of level in the cistern4 ,however1 these novelties have not been sufficiently tried to determine their practical value for strictly scientific purposes2 but as weather-glasses1 for showing minute changes1 they are superior to the common barometer4 #df4 ,the ,water-glass ,barometer4--,if a ,florence flask1 having a long neck1 have a small quantity of water poured into it1 and then be inverted and so supported that the open end dips into a vessel containing water1 a small column of water will be confined in the neck of the bottle1 the pressure of which1 upon the surface of the exposed water1 will be equal to the difference between the atmospheric pressure and the elasticity of the confined air in the body of the bottle4 ,as the pressure of the atmosphere varies1 this column will alter in height4 ,but the elasticity of the confined air is also subject to variations1 owing to changes of temperature4 ,it follows1 then1 that the oscillations of the column are dependent on alterations of temperature and atmospheric pressure4 ,such an arrangement has been called the ,water-glass ,barometer1 and bears about the same relative value to the mercurial barometer1 as an exponent of weather changes1 that a cat-gut hygrometer bears to a thermometric hygrometer1 as an indicator of relative moisture4 #dg4 ,,sympiesometer4 ,nevertheless the instrument now about to be described1 depending upon similar principles1 but scientifically constructed and graduated1 is a very useful and valuable substitute for the mercurial barometer4 ,it consists of a glass tube1 varying1 according to the purposes for which the instrument is required1 from six to twenty-four inches in length4 ,the upper end is closed1 and formed into a bulb2 the lower is turned up1 formed into a cistern1 and open at top1 through a pipette1 or cone4 ,a plug1 moveable by a catch from below1 can be made to close this opening1 so as to render the instrument portable4 ,illustration3 ,fig4 #cb4 ,the upper portion of the tube is filled with air2 the lower portion1 and part of the cistern1 with sulphuric acid1 coloured so as to render it plainly visible4 ,formerly1 hydrogen and oil were used4 ,it was found1 however1 that1 by the process known to chemists as osmosis1 this light gas in time partially escaped1 and the remainder became mixed with air1 the consequence being that the graduations were no longer correct4 ,they are more durable as at present constructed4 ,the liquid rises and falls in the tube with the variations of atmospheric pressure and temperature acting together4 ,if the pressure were constant1 the confined air would expand and contract for temperature only1 and the instrument would act as a thermometer4 ,in fact1 the instrument is regarded as such in the manufacture2 and the thermometric scales are ascertained and engraved on the scale4 ,a good mercurial thermometer is also mounted on the same frame4 ,if1 therefore1 at any time the mercurial and the air thermometers do not read alike1 it must evidently be due to the atmospheric pressure acting upon the air in the tube2 and it is further evident that1 under these circumstances1 the position of the top of the liquid may be marked to represent the barometric pressure at the time4 ,in this manner a scale of pressure is ascertained by comparison with a standard barometer1 extending generally from #bg to #ca inches4 ,when made correctly1 these instruments agree well with the mercurial barometer for a number of years1 and their subsequent adjustment is not a matter of much expense4 ,for use at sea1 the liquid column is contracted at the bend4 ,the sympiesometer is very sensitive1 and feels the alterations in the atmospheric pressure sooner than the ordinary marine barometer4 ,the scale is usually on silvered brass1 mounted on a mahogany or rosewood frame1 protected in front by plate glass4 ,it is generally furnished with a revolving register1 to record the observation1 in order that it may be known whether the pressure has increased or decreased in the interval of observation4 ,small pocket sympiesometers are sometimes fitted with ivory scales1 and protected by a neat velvet-lined pasteboard or morocco case4 ,how to take an ,observation4--,in practice1 the indications of the atmospheric pressure are obtained from the sympiesometer by noting1 first1 the temperature of the mercurial thermometer2 secondly1 adjusting the pointer of the pressure scale to the same degree of temperature on the scale of the air column2 thirdly1 reading the height of the liquid on the sliding scale4 ,directions for ,use4--,the sympiesometer should be carried and handled so as to keep the top always upwards1 to prevent the air mechanically mixing with the liquid4 ,care should also be taken to screen it from casual rays of the sun or cabin fire4 #dh4 ,,aneroids4 ,the beautiful and highly ingenious instrument called by the name ,aneroid1 is no less remarkable for the scientific principles of its construction and action1 than for the nicety of its mechanism4 ,it is a substitute1 and perhaps the best of all substitutes1 for the mercurial barometer4 ,as its name implies1 it is constructed without fluid4 ,it was invented by ,m4 ,vidi of ,paris4 ,in the general form in which it is made it consists of a brass cylindrical case about four inches in diameter and one and a half inch deep1 faced with a dial graduated and marked similarly to the dial-plate of a wheel-barometer1 upon which the index or pointer shows the atmospheric pressure in inches and decimals of an inch in accordance with the mercurial barometer4 ,within the case1 for ordinary sizes1 is placed a flat metal box1 generally not more than half an inch thick and about two inches or a little more in diameter1 from which nearly all the air is exhausted4 ,the top and bottom of this box is corrugated in concentric circles1 so as to yield inwardly to external pressure1 and return when the pressure is removed4 ,the pressure of the atmosphere1 acting externally1 continually changes1 while the elastic pressure of the small quantity of air within can only vary by its volume being increased or decreased1 or by change of temperature4 ,leaving out of consideration1 for the moment1 the effect of temperature1 we can readily perceive that as the pressure is lessened upon the outside of the box1 the elastic force of the air within will force out the top and bottom of the box2 and when the outer pressure is increased they will be forced in4 ,thus with the varying pressure of the atmosphere1 the top and bottom of the box approach to and recede from each other by a small quantity2 but the bottom being fixed1 nearly all this motion takes place on the top4 ,thus the top of the box is like an elastic cushion1 which rises and falls according as the compressing force lessens or increases4 ,to the eye these expansions and contractions would not be perceptible1 so small is the motion4 ,but they are rendered very evident by a nice mechanical arrangement4 ,to the box is attached a strong piece of iron1 kept pressed upon it by a spring at one extremity2 so that as the top of the box rises1 the motion is made sensible at the point held by the spring1 and when the top descends the spring draws the piece of iron into close contact with it4 ,this piece of iron acts as a lever1 having its fulcrum at one extremity1 the power at the centre of the box-top1 and the other extremity controlled by the spring4 ,thus it is evident that the small motion of the centre of the box-top is much increased at the spring extremity4 ,the motion thus obtained is communicated to a system of levers2 and1 by the intervention of a piece of watch-chain and a fine spring passing round the arbour1 turns the index to the right or left1 according as the external pressure increases or decreases4 ,thus1 when by increase of pressure the vacuum box is compressed1 the mechanism transfers the movement to the index1 and it moves to the right2 when the vacuum box bulges out under diminished pressure1 the mechanical motion is reversed1 and the index moves to the left4 ,as the index traverses the dial1 it shows upon the scale the pressure corresponding with that which a good mercurial barometer would at the same time and place indicate2 that is1 supposing it correctly adjusted4 ,a different and more elegant arrangement has since been adopted4 ,a broad curved spring is connected to the top of the vacuum box1 so as to be compressed by the top of the box yielding inward to increased pressure1 and to relax itself and the box as the pressure is lessened4 ,the system of levers is connected to this spring1 which augments and transfers the motion to the index1 in the manner already described4 ,increase of pressure causes the levers to slacken the piece of watch-chain connected with them and the arbour of the index4 ,the spring now uncoils1 winds the chain upon the arbour1 and turns the index to the right4 ,decrease of pressure winds the chain off the barrel1 tightens the spiral spring1 which thus turns the index to the left4 ,the graduations of the aneroid scale are obtained by comparisons with the correct standard reading of a mercurial barometer1 under the normal and reduced atmospheric pressure4 ,reduced pressure is obtained by placing both instruments under the receiver of an air pump4 ,illustration3 ,fig4 #cc4 ,fig4 #cc represents the latest improved mechanism of an aneroid4 ,the outer case and the face of the instrument are removed1 but the hand is attached by its collet to the arbour4 ,a is the corrugated box1 which has been exhausted of air through the tube1 ,j1 and hermetically sealed by soldering4 ,b is a powerful curved spring1 resting in gudgeons fixed on the frame-plate1 and attached to a socket behind1 ,f1 in the top of the box4 ,a lever1 ,c1 joined to the stout edge of the spring1 is connected1 by the bent lever at ,d1 with the chain1 ,e1 the other end of which is coiled round1 and fastened to the arbour1 ,f4 ,as the box1 ,a1 is compressed by the weight of the atmosphere increasing1 the spring1 ,b1 is tightened1 the lever1 ,c1 depressed1 and the chain1 ,e1 uncoiled from ,f1 which is thereby turned so that the hand1 ,h1 moves to the right4 ,in the mean while the spiral spring1 ,g1 coiled round ,f1 and fixed at one extremity to the frame-work and by the other to ,f1 is compressed4 ,when1 therefore1 the pressure decreases1 ,a and ,b relax1 by virtue of their elasticity2 ,e slackens1 ,g unwinds1 turning ,f1 which carries ,h to the left4 ,near ,j is shown an iron pillar1 cast as part of the stock of the spring1 ,b4 ,a screw works in this pillar through the bottom of the plate1 by means of which the spring1 ,b1 may be so adjusted to the box1 ,a1 as to set the hand1 ,h1 to read on the scale according to the indications of a mercurial barometer4 ,the lever1 ,c1 is composed of brass and steel1 soldered together1 and adjusted by repeated trials to correct for the effects of temperature4 ,a thermometer is sometimes attached to the aneroid1 as it is convenient for indicating the temperature of the air4 ,as regards the instrument itself1 no correction for temperature can be applied with certainty4 ,it should be set to read with the mercurial barometer at #cb deg4 ,f4 ,then the readings from it are supposed to require no correction4 ,in considering the effects of temperature upon the aneroid1 they are found to be somewhat complex4 ,there is the effect of expansion and contraction of the various metals of which the mechanism is composed2 and there is the effect on the elasticity of the small portion of air in the box4 ,an increase of temperature produces greater1 a diminution less elasticity in this air4 ,the compensation for effects of temperature is adjusted by the process of trial and error1 and only a few makers do it well4 ,it is very often a mere sham4 ,admiral ,fitz,roy writes1 in his ,barometer ,manual1 ,the known expansion and contraction of metals under varying temperatures1 caused doubts as to the accuracy of the aneroid under such changes2 but they were partly removed by introducing into the vacuum box a small portion of gas1 as a compensation for the effects of heat or cold4 ,the gas in the box1 changing its bulk on a change of temperature1 was intended to compensate for the effect on the metals of which the aneroid is made4 ,besides which1 a further and more reliable compensation has lately been effected by a combination of brass and steel bars4 ,aneroid barometers1 if often compared with good mercurial columns1 are similar in their indications1 and valuable2 but it must be remembered that they are not independent instruments1 that they are set originally by a barometer1 require adjustment occasionally1 and may deteriorate in time1 though slowly4 ,the aneroid is quick in showing the variation of atmospheric pressure2 and to the navigator who knows the difficulty1 at times1 of using barometers1 this instrument is a great boon1 for it can be placed anywhere1 quite out of harm's way1 and is not affected by the ship's motion1 although faithfully giving indication of increased or diminished pressure of air4 ,in ascending or descending elevations1 the hand of the aneroid may be seen to move 7like the hand of a watch71 showing the height above the level of the sea1 or the difference of level between places of comparison4 ,in the admiral's ,notes on ,meteorology1 he says1 ,the aneroid is an excellent weather glass1 if well made4 ,compensation for heat or cold has lately been introduced by efficient mechanism4 ,in its improved condition1 when the cost may be about ,l#e1 it is fit for measuring heights as far as #e1jjj feet with approximate accuracy2 but even at the price of ,l#c1 as a weather-glass only1 it is exceedingly valuable1 because it can be carried anywhere2 and if now and then compared with a good barometer1 it may be relied on sufficiently4 ,i have had one in constant use for ten years1 and it appears to be as good now as at first4 ,for a ship of war 7considering concussion by the fire of guns71 for boats1 or to put in a drawer1 or on a table1 ,i believe there is nothing better than it for use as a common weather-glass4 ,colonel ,sir ,h4 ,james1 ,r4,e41 in his ,instructions for taking ,meteorological ,observations1 says of the aneroid1 ,this is a most valuable instrument2 it is extremely portable4 ,i have had one in use for upwards of ten years1 and find it to be the best form of barometer1 as a weather-glass1 that has been made4 ,one of the objects of ,mr4 ,glaisher's experiments in balloons was to compare the readings of an aneroid barometer with those of a mercurial barometer up to five miles4 ,in the comparisons the readings of the mercurial barometer were corrected for index-error and temperature4 ,the aneroid readings1 says ,mr4 ,glaisher1 prove all the observations made in the several ascents may be safely depended upon1 and also that an aneroid barometer can be made to read correctly to pressures below twelve inches4 ,as one of the general conclusions derived from his experiments he states1 that an aneroid barometer read correctly to the first place1 and probably to the second place of decimals1 to a pressure as low as seven inches4 ,the two aneroids used by ,mr4 ,glaisher were by ,messrs4 ,negretti and ,zambra4 ,aneroids are now manufactured almost perfectly compensated for temperature4 ,such an instrument therefore ought to show the same pressure in the external air at a temperature say of #dj deg41 as it would in a room where the temperature at the same time may be #fj deg42 provided there is no difference of elevation4 ,to test it thoroughly would require an examination and a comparison with barometer readings reduced to #cb deg4 ,f41 conducted through a long range of temperature and under artificially reduced pressure4 ,a practical method appears to be to compare the aneroid daily1 or more often1 for a few weeks with the readings of a mercurial barometer reduced to #cb deg42 and if the error so found be constant1 the object of the compensation may be assumed to be attained1 particularly if the temperature during the period has varied greatly4 ,directions for using the ,aneroid4--,aneroids are generally suspended with the dial vertical2 but if they be placed with the dial horizontal1 the indications differ a few hundredths of an inch in the two positions4 ,hence1 if their indications are registered1 they should be kept in the same position4 ,the aneroid will not answer for exact scientific purposes1 as it cannot be relied upon for a length of time4 ,its error of indication changes slowly1 and hence the necessity of its being set from time to time with the reading of a good barometer4 ,to allow of this being done1 at the back of the outer case is the head of a screw in connection with the spring attached to the vacuum box4 ,by applying a small turnscrew to this screw1 the spring of the vacuum box may be tightened or relaxed1 and the index made to move correspondingly to the right or left on the dial4 ,by this means1 besides being enabled to correct the aneroid at any time1 if the measure of a height rather greater than the aneroid will commonly show be required1 it may be re-set thus3 ,when at the upper station 7within its range71 and having noted the reading carefully1 touch the screw behind so as to bring back the hand a few inches 7if the instrument will admit71 then read off and start again4 ,reverse the operation when descending4 ,this may add some inches of measure approximately4--,fitz,roy4 ,illustration3 ,fig4 #cd4 #di4 ,small ,size ,aneroids4--,the patent for the ,aneroid having expired1 ,admiral ,fitz,roy urged upon ,messrs4 ,negretti ,zambra the desirability of reducing the size at which it had hitherto been made1 as well as of improving its mechanical arrangement1 and compensation for temperature4 ,they accordingly engaged skilful workmen1 who1 under their directions1 and at their expense1 by a great amount of labour and experiment1 succeeded in reducing its dimensions to two inches in diameter1 and an inch and a quarter thick4 ,the exact size and appearance of this aneroid are shown in fig4 #cd4 ,the compensation is carefully adjusted1 and the graduations of the dial ascertained under reduced pressure1 so that they are not quite equal1 but more accurate4 #ej4 ,watch ,aneroid4--,subsequently the aneroid has been further reduced in size and it can now be had from an inch and a quarter to six inches in diameter4 ,the smallest size can be enclosed in watch cases1 fig4 #ce1 or otherwise1 so as to be adapted to the pocket4 ,by a beautifully simple contrivance1 a milled rim is adjusted to move round with hand pressure1 and carry a fine index or pointer1 outside and around the scale engraved on the dial1 or face1 for the purpose of marking the reading1 so that the subsequent increase or decrease of pressure may be readily seen4 ,these very small instruments are found to act quite as correctly as the largest1 and are much more serviceable4 ,besides serving the purpose of a weather-glass in the house or away from home1 if carried in the pocket1 they are admirably suited to the exigencies of tourists and travellers4 ,they may be had with scale sufficient to measure heights not exceeding #h1jjj feet2 with a scale of elevation in feet1 as well as of pressure in inches1 engraved on the dial4 ,the scale of elevation1 which is for the temperature of #ej deg41 was computed by ,professor ,airy1 the ,astronomer ,royal1 who kindly presented it to ,messrs4 ,negretti and ,zambra1 at the same time suggesting its application4 ,moderate-sized aneroids1 fitted in leathern sling cases1 are also good travelling instruments1 and will be found serviceable to pilots1 fishermen1 and for use in coasting and small vessels1 where a mercurial barometer cannot be employed1 because requiring too much space4 ,illustration3 ,fig4 #ce4 ,admiral ,fitz,roy1 in a communication to the ,mercantile ,marine ,magazine1 ,december1 #ahfj1 says3--,aneroids are now made more portable1 so that a pilot or chief boatman may carry one in his pocket1 as a railway guard carries his timekeeper2 and1 thus provided1 pilots cruising for expected ships would be able to caution strangers arriving1 if bad weather were impending1 or give warning to coasters or fishing boats4 ,harbours of ,refuge1 however excellent and important1 are not always accessible1 even when most wanted1 as in snow1 rain1 or darkness1 when neither land1 nor buoy1 nor even a lighthouse-light can be seen4 #ea4 ,measurement of ,heights by the ,aneroid4--,for measuring heights not exceeding many hundred feet above the sea-level by means of the aneroid1 the following simple method will suffice3-- ,divide the difference between the aneroid readings at the lower and upper stations by 4#jjaa2 the quotient will give the approximate height in feet4 ,thus1 supposing the aneroid to read at the ,lower ,station #cj4che inches4 ,upper ,station #cj4jbe ------ ,difference 4#cfj ,divided gives 4#cfj_/4jjaa #cbg feet4 ,as an illustration of the mode in which the aneroid should be used in measuring heights1 the following example is given3-- ,a gentleman who ascended ,helvellyn1 ,august #abth1 #ahfb1 recorded the following observations with a pocket aneroid by ,negretti and ,zambra3-- ,near #aj a4m41 at the first milestone from ,ambleside1 found by survey to be #ahh feet above the sea1 the aneroid read #bi4hi inches2 about #a p4m41 at the summit of ,helvellyn1 #bf4ha2 and at #e p4m41 at the milestone again1 #bi4gf4 ,the temperature of the lower air was #eg deg41 of the upper1 #ed deg4 ,hence the height of the mountain is deduced as follows3-- ,inches4 ,reading at #aj a4m4 #bi4hi #e p4m4 #bi4gf ------ ,mean #bi4hbe ,table ,i4#e #ajaj ,upper ,reading #bf4ha #cgif ----- ,difference #bghf ,mean ,temperature #ee deg4#e1 gives in ,table ,,ii4 #a4jdh ----- #bibj ,lat4 #ee deg4 ,n41 gives in ,table ,,iii4 4#iiia ----- #biag ,table ,,iv4 #e ----- ,difference of height #bibb ,height of lower station #ahh ----- ,helvellyn #caaj ,in ,sir ,j4 ,herschell's ,physical ,geography it is given as #caae ft4 ,so near an agreement is attributable to the excellence of the aneroid1 and the careful accuracy of the observer4 #eb4 ,,metallic ,,barometer4 ,this instrument1 the invention of ,m4 ,bourdon1 has a great resemblance to the aneroid1 but is much simpler in arrangement4 ,the inventor has applied the same principle to the construction of metallic steam-pressure gauges4 ,we are here1 however1 only concerned with it as constructed to indicate atmospheric pressure4 ,it consists of a long slender flattened metallic tube1 partially exhausted of air1 and hermetically closed at each end1 then fixed upon its centre1 and bent round so as to make the ends face each other4 ,the transverse section of this tube is an elongated ellipse4 ,the principle of action is this3 interior pressure tends to straighten the tube1 external pressure causes it to coil more4 ,hence as the atmospheric pressure decreases1 the ends of the tube become more apart4 ,this movement is augmented and transferred by a mechanical arrangement of small metallic levers to a radius bar1 which carries a rack formed on the arc of its circle4 ,this moves a pinion1 upon the arbour of which a light pointer1 or hand1 is poised1 which indicates the pressure upon a dial4 ,when the pressure increases1 the ends of the tube approach each other1 and the pointer moves from left to right over the dial4 ,the whole mechanism is fixed in a brass case1 having a hole at the back for adjusting the instrument to the mercurial barometer by means of a key1 which sets the pointer without affecting the levers4 ,the dial is generally open to show the mechanism1 and is protected by a glass1 to which is fitted a moveable index4 ,this barometer is very sensitive1 and has the advantage of occupying little space1 although it has not yet been made so small as the aneroid4 ,both these instruments admit of a great variety of mounts to render them ornamental4 ,the metallic barometer can be constructed with a small clock in its centre1 so as to form a novel and beautiful drawing-room ornament4 ,admiral ,fitz,roy writes1 ,metallic barometers1 by ,bourdon1 have not yet been tested in very moist1 hot1 or cold air for a sufficient time4 ,they are dependent1 or secondary instruments1 and liable to deterioration4 ,for limited employment1 when sufficiently compared1 they may be very useful1 especially in a few cases of electrical changes1 not foretold or shown by mercury1 which these seem to indicate remarkably4 ,they are not so well adapted for travellers1 nor for measurements of considerable elevations1 as aneroids4 ,,chapter ,,vi4 ,,instruments ,,for ,,ascertaining ,,temperature4 #ec4 ,temperature is the energy with which heat affects our sensation of feeling4 ,bodies are said to possess the same temperature1 when the amounts of heat which they respectively contain act outwardly with the same intensity of transfer or absorption1 producing in the one case the sensation of warmth1 in the other that of coldness4 ,instruments used for the determination and estimation of temperatures are called ,thermometers4 ,experience proves that the same body always occupies the same space at the same temperature2 and that for every increase or decrease of its temperature1 it undergoes a definite dilatation or contraction of its volume4 ,provided1 then1 a body suffers no loss of substance or peculiar change of its constituent elements or atoms1 while manifesting changes of temperature it will likewise exhibit alterations in volume2 the latter may1 therefore1 be taken as exponents of the former4 ,the expansion and contraction of bodies are adopted as arbitrary measures of changes of temperature2 and any substance will serve for a thermometer in which these changes of volume are sensible1 and can be rendered measureable4 #ed4 ,thermometric ,substances4--,thermometers for meteorological and domestic purposes are constructed with liquids1 and generally either mercury or alcohol1 because their alterations of volume for the same change of temperature are greater than those of solids2 while being more manageable1 they are preferred to gases4 ,mercury is of all substances the best adapted for thermometric purposes1 as it maintains the liquid state through a great alteration of heat1 has a more equable co-efficient of expansion than any other fluid1 and is peculiarly sensitive to changes of temperature4 ,the temperature of solidification of mercury1 according to ,fahrenheit's scale of temperature1 is -#dj deg42 and its temperature of ebullition is about #fjj deg4 ,sulphuric ether1 nitric acid1 oil of sassafras1 and other limpid fluids1 have been employed for thermometers4 #ee4 ,description of the ,thermometer4--,the ordinary thermometer consists of a glass tube of very fine bore1 having a bulb of thin glass at one extremity1 and closed at the other4 ,the bulb and part of the tube contains mercury2 the rest of the tube is a vacuum1 and affords space for the expansion of the liquid4 ,this arrangement renders very perceptible the alterations in volume of the mercury due to changes of temperature4 ,it is true1 the glass expands and contracts also2 but only by about one-twentieth of the extent of the mercury4 ,regarding the bulb1 then1 as unalterable in size1 all the changes in the bulk of the fluid must take place in the tube1 and be exhibited by the expansion and contraction of the column1 which variations are made to measure changes of temperature4 #ef4 ,,standard ,,thermometer4 ,the peculiarities in the construction of thermometers will be best understood by describing the manufacture of a ,standard ,thermometer1 which is one of the most accurate make1 and the scale of which is divided independently of any comparison with another thermometer4 ,fig4 #cf is an illustration of such an instrument1 on a silvered brass scale4 ,illustration3 ,fig4 #cf ,selection of ,tube4--,in selecting the glass tube1 much care is requisite to ascertain that its bore is perfectly uniform throughout4 ,as received from the glass-house1 the tubes are generally1 in their interior1 portions of very elongated cones1 so that the bore is wider at one end than at the other4 ,with due care1 however1 a proper length of tube can be selected1 in which there is no appreciable difference of bore4 ,this is ascertained by introducing into the tube a length of mercury of about a half or a third of an inch1 and accurately measuring it in various positions in the tube4 ,to accomplish this1 the workman blows a bulb at one end of the tube1 and heats the bulb a little to drive out some of the air4 ,then1 placing the open end in mercury1 upon cooling the elasticity of the enclosed air diminishes1 and the superior pressure of the atmosphere drives in some mercury4 ,the workman stops the process so soon as he judges sufficient mercury has entered4 ,by cooling or heating the bulb1 as necessary1 the mercury is made to pass from one end of the tube to the other4 ,should the length of this portion of mercury alter in various parts of the bore1 the tube must be rejected4 ,if it is1 as nearly as possible1 one uniform length1 the tube is set aside for filling4 ,the bulb is never blown by the breath1 but by an elastic caoutchouc ball containing air1 so that the introduction of moisture is avoided4 ,the spherical form is to be preferred2 for it is best adapted to resist the varying pressure of the atmosphere4 ,the bulbs should not be too large1 or the mercury will take some time to indicate sudden changes of temperature4 ,cylindrical bulbs are sometimes desirable1 as they offer larger surfaces to the mercury1 and enable thermometers to be made more sensitive4 ,the mercury1 with which the bulb is to be filled1 should be quite pure1 and freed from moisture and air by recent boiling4 ,filling the ,tube4--,the filling is effected by heating the bulb with the flame of a spirit-lamp1 while the open end is embedded in mercury4 ,upon allowing the bulb to cool1 the atmospheric pressure drives some mercury into it2 and the process of heating and cooling is thus continued until sufficient mercury is introduced4 ,the mercury is next boiled in the tube1 to expel any air or moisture that may be present4 ,in order to close the tube and exclude all air1 the artist ascertains that the tube contains the requisite quantity of mercury2 then1 by holding the bulb over the spirit flame1 he causes the mercury to fill the whole of the tube1 and dexterously removing it from the source of heat1 he1 at the same instant1 closes it with the flame of a blow-pipe4 ,if any air remain in the tube1 it is easily detected2 for if the instrument be inverted1 the mercury will fall to the extremity of the tube1 if there is a perfect vacuum1 unless the tube be so finely capillary that its attraction for the mercury is sufficient to overcome the force of gravity1 in which case the mercury will retain its position in every situation of the instrument4 ,if1 however1 the mercury fall and does not reach quite to the extremity of the bore1 some air is present1 which must be removed4 ,the ,graduation4--,the thermometer is now prepared for graduation1 the first part of which process is the determination of two fixed points4 ,these are given by the temperatures of melting ice and of the vapour of boiling water4 ,melting ice has always the same temperature in every place and under all circumstances2 provided only that the water from which the ice is congealed is free from salts4 ,the temperature of the vapour of boiling water depends upon the pressure of the atmosphere1 but is always constant for the same pressure4 ,the fixed point corresponding to the temperature of melting ice is called the freezing point4 ,it is obtained by keeping the bulb and the part of the tube occupied by mercury immersed in melting ice1 until the mercury contracts to a certain point1 where it remains stationary4 ,this position of the end of the mercury is then marked upon the tube4 ,the boiling point is not so easily determined1 for the barometer must be consulted about the same time4 ,the boiling apparatus is generally constructed of copper4 ,it consists of a cylindrical boiler1 heated from the base by a spirit lamp or charcoal fire4 ,an open tube two or three inches in diameter and of suitable length enters the top of the boiler4 ,this tube is enveloped by another fixed to the top of the boiler but not opening into it1 and so that the two tubes are about an inch apart4 ,the object of the outer tube is to protect the inner tube from the cold temperature of the air4 ,the outer tube has an opening at the top for the admission of the thermometer1 and a hole near the bottom for the escape of steam through a spout4 ,when the water is made to boil1 the steam rises in the inner tube1 fills the space between the tubes1 and escapes at the spout4 ,the thermometer is then passed down into the inner cylinder1 and held securely from the top by means of a piece of caoutchouc4 ,the tubes or cylinders should be of sufficient length to prevent the thermometer entering the water4 ,this is necessary because the temperature of boiling water is influenced by any substance which it holds in chemical solution2 and1 moreover1 its temperature increases with the depth1 owing to the pressure of the upper stratum4 ,the thermometer being thus surrounded with steam1 the mercury rises in the tube4 ,as it does so1 the tube should be depressed so as always to keep the top of the mercury just perceptible4 ,when the temperature of the vapour is attained1 the mercury ceases to rise1 and remains stationary4 ,the position of the end of the mercury is now marked upon the tube1 and the boiling-point is obtained4 #eg4 ,methods of ascertaining the exact ,boiling ,temperature4--,the normal boiling temperature of water all nations have tacitly agreed to fix under a normal barometric pressure of #bi4ibb inches of mercury1 having the temperature of melting ice1 in the latitude of #de deg41 and at the sea-level4 ,if the atmospheric pressure at the time or place of graduating a thermometer does not equal this1 the boiling temperature will be higher or lower according as the pressure is greater or less4 ,hence a reading must be taken from a reliable barometer1 which must also be corrected for errors and temperature1 and reduced for latitude1 in order to compare the actual atmospheric pressure at the time with the assumed normal pressure4 ,tables of vapour tension1 as they are termed1 have been computed from accurate experimental investigations and theory1--giving the temperatures of the vapour of water for all probable pressures2 ,regnault's1 the most recent1 is considered the most accurate2 and his investigations are based upon the standard pressure given above1 and are for the same latitude4 ,his ,table1 therefore1 will give the temperature on the thermometric scale corresponding to the pressure4 ,the ,commissioners appointed by the ,british ,government to construct standard weights and measures1 decided that the normal boiling-point1 #bab deg41 on the thermometer should represent the temperature of steam generated under an atmospheric pressure equal in inches of mercury1 at the temperature of freezing water1 to #bi4ibb 7cos4 #b latitude x 4#jgff7 74#jjjjjagi x height in feet above the sea-level74 ,hence1 at ,london1 lat4 #ea deg4#cj' ,n41 we deduce #bi4ije as the barometric pressure representing the normal boiling point of water1--the trifling correction due to height being neglected4 ,if then1 in the latitude of ,london1 the barometric pressure1 at the time of fixing the boiling point1 be not #bi4ije inches1 that point will be higher or lower1 according to the difference of the pressure from the normal4 ,near the sea-level about #j4ei inch of such difference is equivalent to #a deg4 ,fahrenheit in the boiling point4 ,suppose1 then1 the atmospheric pressure at ,london to be #cj4ghe inches1 the following calculation gives the corresponding boiling temperature for ,fahrenheit's scale3-- ,observed pressure #cj4ghe ,normal #bi4ije ------ ,difference 4#hhj ,as #j4ei is to #j4hh1 so is #a deg4 to #a deg4#e4 ,that is1 the water boils at #a deg4#e above its normal temperature2 so that1 in this case1 the normal temperature to be placed on the scale1 viz4 #bab deg41 must be #a deg4#e lower than the mark made on the tube at the height at which the mercury stood under the influence of the boiling water4 ,the temperature of the vapour of boiling water may be found1 at any time and place1 as follows3--,multiply the atmospheric pressure by the factor due to the latitude1 given in the annexed ,table ,v41 and with the result seek the temperature in ,table ,,vi4 ,,table ,v4 ,,table ,,vi4 ---------------------------------------- ------------------------ ,latitude4 ,factor4 ,temperature,tension4,temperature,tensio n4 of ,vapour4 of ,vapour4 ---------------------------------------- ---------------- ,degrees4 ,degrees4 ,inches4 ,degrees4 ,inches4 #j #j4iigce #agi #ad4icd #aig #bb4jcf #e #j4iigci #ahj #ae4bga #aih #bb4eja #aj #j4iigea #aha #ae4fad #aii #bb4igd #ae #j4iiggj #ahb #ae4ifc #bjj #bc4def #bj #j4iigig #ahc #af4cah #bja #bc4idf #be #j4iihcj #ahd #af4fhj #bjb #bd4dde #cj #j4iihfh #ahe #ag4jdi #bjc #bd4ieb #ce #j4iiiaj #ahf #ag4dbe #bjd #be4dfh #dj #j4iiied #ahg #ag4hjh #bje #be4iic #de #a4jjjjj #ahh #ah4aig #bjf #bf4ebg #ej #a4jjjdf #ahi #ah4eid #bjg #bg4jgj #ee #a4jjjij #aij #ah4iih #bjh #bg4fbc #fj #a4jjacb #aia #ai4dji #bji #bh4ahe #fe #a4jjagj #aib #ai4hbh #baj #bh4gef #gj #a4jjbjc #aic #bj4bed #baa #bi4cce #ge #a4jjbcj #aid #bj4fhh #bab #bi4ibb #hj #a4jjbdi #aie #ba4abi #bac #cj4eae #aif #ba4egh #bad #ca4aae ---------------------------------------- ------------------------ ,how to use the ,tables4--,when the temperature is known to decimals of a degree1 take out the tension for the degree1 and multiply the difference between it and the next tension by the decimals of the temperature1 and add the product to the tension1 for the degree4 ,required the tension corresponding to #aig deg4#hd4 deg4 #aig #bb4jcf 4#dfe x 4#hd 4#cia #aih #bb4eja #aig deg4 #bb4jcf ------ ------ ,difference 4#dfe #aig4hd #bb4dbg ,when the tension is given1 take the difference between it and the next less tension in the ,table1 and divide this difference by the difference between the next less and next greater tensions4 ,the quotient will be the decimals to add to the degree opposite the next less tension4 ,thus1 for #bc4bad inches1 required the temperature4 ,given #bc4bad ,next greater #bc4def #bb4igd ,next less #bb4igd ------ ------ 4#bdj ,difference 4#dhb 4#bdj ,and ---- 4#e 4#dhb ,temperature opposite next less #aii4j ----- ,temperature required #aii4e ,a similar method of interpolation in taking out numerical quantities is applicable to almost all tables2 and should be practised with all those given in this work4 ,example4--,thus1 in ,liverpool1 lat4 #ec deg4 #cj' ,n41 the barometer reading #bi4hgf inches1 its attached thermometer #ee deg41 and the correction of the instrument being 4#jae 7including index error1 capillarity and capacity71 what temperature should be assigned for the boiling point marked on the thermometer8 ,observed barometer #bi4hgf ,correction 4#jae ------ #bi4hia ,correction for temperature - 4#jgd ------ ,reduced reading #bi4hag ,factor from ,table ,v4 #a4jjjgg ------- #bjhgai #bjhgai #bihag ----------- ,equivalent for lat4 #de deg4 #bi4hciieiji ,in ,table ,,vi41 #bi4hd gives temperature #baa deg4#hf4 #eh4 ,displacement of the ,freezing ,point4--,either the prolonged effect of the atmospheric pressure upon the thin glass of the bulbs of thermometers1 or the gradual restoration of the equilibrium of the particles of the glass after having been greatly disturbed by the operation of boiling the mercury1 seems to be the cause of the freezing points of standard thermometers reading from a few tenths to a degree higher in the course of some years1 as has been repeatedly observed4 ,to obviate this small error1 it is our practice to place the tubes aside for about six months before fixing the freezing point1 in order to give time for the glass to regain its former state of aggregation4 ,the making of accurate thermometers is a task attended with many difficulties1 the principal one being the liability of the zero or freezing point varying constantly1 so much so1 that a thermometer that is perfectly correct to-day1 if immersed in boiling water1 will be no longer accurate2 at least1 it will take some time before it again settles into its normal state4 ,then1 again1 if a thermometer is recently blown1 filled1 and graduated immediately1 or1 at least1 before some months have elapsed1 though every care may have been taken with the production of the instrument1 it will require some correction2 so that the instrument1 however carefully made1 should from time to time be plunged into finely-pounded ice1 in order to verify the freezing point4 #ei4 ,the ,scale4--,the two fixed points having been determined1 it is necessary to apply the scale4 ,the thermometers in general use in the ,united ,kingdom1 the ,british ,colonies1 and ,north ,america are constructed with ,fahrenheit's scale4 ,fahrenheit was a philosophical instrument maker of ,amsterdam1 who1 about the year #agbd1 invented the scale which has given his name to the thermometer4 ,the freezing point is marked #cb deg41 the boiling point #bab deg41 so that the intermediate space is divided into #ahj equal parts1 called degrees4 ,the principle which dictated this peculiar division of the scale is as follows3--,when the instrument stood at the greatest cold of ,iceland1 or #j degree1 it was computed to contain #aaabd equal parts of quicksilver1 which1 when plunged in melting snow1 expanded to #aaaef parts2 hence the intermediate space was divided into #cb equal portions1 and #cb was taken as the freezing point of water3 when the thermometer was plunged in boiling water1 the quicksilver was expanded to #aaccf2 and therefore #bab deg4 was marked as the boiling point of that fluid4 ,in practice1 ,fahrenheit determined the divisions of his scale from two fixed points1 the freezing and boiling of water4 ,the theory of the division1 if we may so speak1 was derived from the lowest cold observed in ,iceland1 and the expansions of a given portion of mercury 7,professor ,trail74 ,the divisions of the scale can be carried beyond the fixed points1 if requisite1 by equal graduations4 ,fahrenheit's scale is very convenient in some respects4 ,the meteorological observer is seldom troubled with negative signs1 as the zero of the scale is much below freezing4 ,again1 the divisions are more numerous1 and consequently smaller1 than on other scales in use2 and the further subdivision into tenths of degrees1 seems to give all the minuteness usually required4 ,celcius1 a ,swede1 in #agdb1 proposed zero for the freezing point1 and #ajj for the boiling point1 all temperatures below zero being distinguishable by the sign 7--7 minus4 ,this scale is known as the centigrade1 and is in use in ,france1 ,sweden1 and the southern part of ,europe4 ,it has the advantage of the decimal notation1 with the embarrassment of the negative sign4 ,reaumur1 a ,frenchman1 proposed zero for the freezing point1 and #hj deg4 for the boiling point1 an arrangement inferior to the centigrade4 ,it is1 however1 in use in ,spain1 ,switzerland1 and ,germany4 ,it is merely a simple arithmetical operation to change the indications of any one of these scales into the equivalents on the others4 ,to facilitate such conversions1 tables are convenient1 when a large number of observations are under discussion2 and they can be easily formed or obtained4 ,in the absence of such tables1 the following formulae will insure accuracy of method1 and save thinking1 when occasional conversions are wanted to be made3--,f4 stands for ,fahrenheit1 ,c4 for ,centigrade1 and ,r4 for ,reaumur4 ,given4 ,required4 ,solution4 ,f4 ,c4 7,f4-#cb7 #e_/i ,f4 ,r4 7,f4-#cb7 #d_/i ,c4 ,f4 #i_/e ,c4 #cb ,c4 ,r4 #d_/e ,c4 ,r4 ,f4 #i_/e ,r4 #cb ,r4 ,c4 #e_/d ,r4 ,example4--,convert #be deg4 of ,fahrenheit's scale into the corresponding temperature on the ,centigrade scale4 ,here ,c4 7#be - #cb7 #e_/i ,c4 -#ce_/i -#c4i or nearly #d deg4 below zero of the ,centigrade scale4 ,the algebraical sign must be carefully attended-to in the calculations4 #fj4 ,the method of testing ,thermometers for meteorological purposes is very simple4 ,such thermometers are seldom required to read above #abj deg4 ,in these the freezing point having been determined1 the divisions of the scale are ascertained by careful comparisons1 with a standard thermometer1 in water of the requisite temperature4 ,for the freezing point1 the bulbs1 and a considerable portion of the tubes of the thermometers1 are immersed in pounded ice4 ,for the higher temperatures1 the thermometers are placed in a cylindrical glass vessel containing water of the required heat3 the scales of the thermometers intended to be tested1 together with the ,standard with which they are to be compared1 are read through the glass4 ,in this way the scale readings may be tested at any required degree of temperature1 and the usual practice is to test them at every ten degrees from #cb deg4 to #ib deg4 of ,fahrenheit4--,fitz,roy4 #fa4 ,porcelain ,scale ,plates4--,thermometer scales of brass1 wood1 or ivory1 either by atmospheric influence or dipping in sea-water1 are very liable to become soiled and discoloured1 so much so that after a very little time the divisions are rendered nearly invisible4 ,to obviate this inconvenience1 ,messrs4 ,negretti and ,zambra were the first to introduce into extensive use thermometer and barometer scale-plates made of porcelain1 having the divisions and figures engraved thereon by means of fluoric acid1 and permanently burnt-in and blackened1 so as always to present a clear legible scale4 ,that these scales have been found superior to all others1 may be inferred from the fact that all the thermometers now supplied to the various government departments are provided with such scales4 ,they can be adapted to replace any of the old forms of brass or zinc scales1 the divisions and figures of which have become obliterated or indistinct4 #fb4 ,enamelled ,tubes4--,nearly all thermometer tubes are now made with enamelled backs4 ,this contrivance of enamelling the backs of the tubes enables the makers to use finer threads of mercury than had before been found practicable2 for were it not for the great contrast between the dark thread of mercury and the white enamel on the glass1 many of the thermometers now in use would be positively illegible4 ,the enamelling of thermometers is an invention of ,messrs4 ,negretti and ,zambra4 ,it is necessary to state this1 as many persons1 from interested motives1 are anxious to ignore to whom the credit of the invention is due4 #fc4 ,thermometers of extreme ,sensitiveness4--,thermometers for delicate experiments are no novelty4 ,thermometers have been made with very delicate bulbs to contain a very small quantity of mercury4 ,such instruments have also been made with spiral or coiled tubular bulbs1 but the thickness of glass required to keep these coils or spirals in shape1 and in fact to prevent their falling to pieces1 served to nullify the effect sought to be produced1 viz4 instantaneous action2 and where a small thin bulb was employed1 the indicating column was generally so fine that it was positively invisible except by the aid of a powerful lens4 ,messrs4 ,negretti and ,zambra have now introduced a new form of thermometer1 which combines sensitiveness and quickness of action1 together with a good visible column4 ,the bulb of this thermometer is of the gridiron form4 ,care has been taken in constructing the bulb1 so that the objections attending spirals and other forms have been overcome2 for whilst the reservoir or bulb is made of glass so thin that it is only by a spirit lamp and not a glass blower's blowpipe that it can be formed1 yet it is still so rigid 7owing to its peculiar configuration7 that no variations in its indications can be detected1 whether it be held in a horizontal1 vertical1 or oblique position1 nor will any error be detected if it be stood on its own bulb4 ,they have made thermometers with bulbs or reservoirs formed of about nine inches of excessively thin cylindrical glass1 whose outer diameter is not more than a twentieth of an inch2 so that1 owing to the large surface presented1 the indications are positively instantaneous4 ,this form of thermometer was constructed expressly to meet the requirements of scientific balloon ascents1 to enable thermometrical readings to be taken at the precise elevation4 ,it was contemplated to procure a metallic thermometer1 but on the production of this perfect instrument the idea was abandoned4 #fd4 ,,varieties ,,of ,,thermometers4 ,fig4 #cg is an illustration of boxwood scale thermometers for general use and common purposes4 ,fig4 #ch1 ,negretti and ,zambra's ,travelling ,thermometer2 it is fixed in a plated metal 7silver or otherwise7 case1 similar to a pencil-case1 and has the scale divided upon its stem4 ,fig4 #ci1 ,thermometer mounted on a slab of glass1 upon which the scale is etched1 the back being either oak1 mahogany1 or ebony4 ,fig4 #dj1 ,portable ,thermometer1 in a bronzed brass or ,german silver revolving case4 ,fig4 #da1 ,pocket ,thermometer1 on ivory or metallic scale1 in morocco or papier-mache case4 ,illustration3 ,fig4 #cg4 ,illustration3 ,fig4 #ch4 ,illustration3 ,fig4 #ci4 ,illustration3 ,fig4 #dj4 ,illustration3 ,fig4 #da4 ,fig4 #db1 an ,ornamental ,drawing-room ,thermometer1 on ebony or ivory stand1 with glass shade4 ,fig4 #dc1 representation of highly carved or engine-turned design for thermometer mounts1 in ivory or wood1 for the drawing-room4 ,some have the addition of a sundial or compass at the top2 they may also be formed for a watch-stand4 ,fig4 #dd1 ,bath ,thermometer1 having a float to admit of its being kept in the water4 ,illustration3 ,fig4 #db4 ,illustration3 ,fig4 #dc4 ,illustration3 ,fig4 #dd4 ,fig4 #de1 ,thermometer with ivory scale in glass cylinder1 mounted on oak bracket with metal top1 for out-door use2 as at a window4 ,fig4 #df1 ,thermometer for the window1 on patent porcelain or glass scale1 with oak bracket and convenient brass supports1 for placing the instrument at any angle4 ,fig4 #dg1 ,chemical ,thermometer1 on boxwood scale1 jointed near the bulb on a brass hinge1 ranging from #cjj deg4 to #fjj deg4 ,fig4 #dh1 ,chemical ,thermometer1 for acids1 graduated on its own stem1 suitable for insertion in the tubulure of retorts2 they are also made insulated in glass cylinder to protect the graduated stem2 ranging from #j deg4 to #fjj deg4 ,illustration3 ,fig4 #de4 ,illustration3 ,fig4 #df4 ,illustration3 ,fig4 #dg4 ,illustration3 ,fig4 #dh4 ,illustration3 ,fig4 #di4 ,illustration3 ,fig4 #ej4 #fe4 ,superheated ,steam ,thermometer4--,the great advantage gained by the use of superheated steam in marine and other steam-engines being now generally admitted by engineers1 reliable thermometers1 reading to #fjj deg4 at least1 are of the utmost importance4 ,to meet this want1 ,messrs4 ,negretti and ,zambra have constructed for the purpose a substantial form of thermometer1 on their patent porcelain scales1 in strong and convenient metal mountings1 with perforated protection to the bulb4 ,the scales cannot be deteriorated by steam1 heat1 oil1 or dirt2 and an occasional wiping will be all that is necessary to keep the divisions and figures clean and visible for any length of time2 while careful calibration of the thermometer tubes ensures the most accurate indications attainable4 ,these thermometers are illustrated by figs4 #di #ej4 ,a similar1 but cheaper1 construction is given to thermometers to be used with hot air1 or hot water1 apparatus4 #ff4 ,thermometer for ,sugar ,boiling is protected by a metallic frame2 and is usually from three to four feet long1 the graduations being confined to a space of about twelve inches at the upper part of the instrument1 allowing the bulb and greater part of the tube to be immersed in the boiling sugar4 ,the graduations extend to #bgj deg4 or further4 ,an index is sometimes attached to the scale1 which may be set to any degree of heat required to be maintained4 #fg4 ,,earth ,,thermometer4 ,the ,earth ,thermometer is for ascertaining the temperature of the soil at various depths4 ,it is protected by a brass frame1 pointed and strengthened at the end to facilitate insertion into the ground1 as in fig4 #ea4 ,illustration3 ,fig4 #ea4 ,utility of a ,knowledge of the ,temperature of the ,soil4--,the temperature of the soil is an important element in the consideration of climate1 as it concerns the vegetable kingdom4 ,dr4 ,daubeny1 in his ,lectures on ,climate1 gives the following statement with respect to some temperatures which have been observed just beneath the earth's surface1 in different parts of the globe3-- ---------------------------------------- ---------------------------- ,country4 ,temperature4 ,authority4 ---------------------------------------- --------------------------- ,tropics1 often #afb-ahd deg4 ,humboldt4 ,egypt #acc-add ,edwards ,colin4 ,orinoco ,in white sand1 #adj ,humboldt4 ,chili #aac-aah1 among dry grass ,boussingault4 ,cape of ,good ,hope#aej1 under the soil of a bulb ,herschell4 garden ,bermuda #adb1 thermometer barely covered ,emmet4 in earth ,china ,water of the fields1 #aac2 ,meyer4 adjacent sand1 much higher2 blackened sides of the boat at midday1 #adb-aej ,france #aah-abb1 and in one instance #abg ,arago4 ---------------------------------------- ---------------------------- ,the importance of this to vegetation may be estimated by the following considerations3-- ,it is known that every plant requires a certain amount of heat1 varying in the case of each species1 for the renewal of its growth1 at the commencement of the season4 ,now when this degree of heat has spurred into activity those parts that are above ground1 and caused them to elaborate the sap1 it is necessary that the subterranean portions should at the same time be excited by the heat of the ground to absorb the materials which are to supply the plant with nourishment4 ,unless the latter function is provided for1 the aerial portions of the plant will languish from want of food to assimilate4 ,indeed1 it is even advisable that the roots should take the start of the leaves1 in order to have in readiness a store of food for the latter to draw upon4 ,in another place the professor remarks3--,it has been calculated by ,mr4 ,raikes1 from experiments made at ,chat ,moss1 that the temperature of the soil when drained averages #aj deg4 more than it does when undrained2 and this is not surprising1 when we find that #a lb4 of water evaporated from #a1jjj lbs4 of soil will depress the whole by #aj deg41 owing to the latent heat which it absorbs in its conversion into vapour4 #fh4 ,,marine ,,thermometer4 ,this instrument is a special construction to meet the requirements of navigation4 ,it consists of a carefully constructed thermometer divided on its stem to degrees1 which are sufficiently large to admit of subdivision into tenths of degrees by estimation1 and ranging from #j deg4 to #acj deg4 ,the scale is porcelain1 having the degrees etched upon it1 and burnt-in a permanent black4 ,the instrument is made to slide into a japanned metallic case1 for handy use and protection4 ,it is therefore adapted for almost any ordinary purpose2 and cannot be injuriously affected by any chemical action arising from air or sea-water4 ,a set of these thermometers consists of six1 carefully packed in a neat box2 two having japanned metallic cases 7fig4 #eb71 the others being designed for use without the case1 or to replace a breakage4 ,illustration3 ,fig4 #eb4 ,this thermometer is employed in the ,royal ,navy1 and for the observations made at sea for the ,board of ,trade4 ,the thermometer is now considered a necessary instrument on board ship4 ,not only is it of invaluable utility in connection with the barometer as a guide to the weather1 but its indications are of service in showing the presence of a warm or cold current in the sea2 many of the great oceanic currents being characterised by the warmth or coldness of their waters4 ,in seas visited by icebergs1 the habitual use of the thermometer would indicate their proximity1 as the water is rendered colder for some distance around by the thawing of huge masses of ice4 ,the water over a shoal in the sea is generally colder than the surface-water of the surrounding ocean2 which may result from the cold water being brought to the surface by the current of water encountering the shoal4 ,with this fact navigators are well acquainted2 and therefore a fall in the sea-water thermometer may forebode that shallow water is at hand4 ,it has been ascertained that fish inhabit regions of the oceans and seas having the peculiar temperature suitable to their habits4 ,the better and firmer sort of fish are found where cold waters exist4 ,those taken in warmer belts or streams of water1 even in the same latitude1 are far inferior in condition1 and less approved by the palate4 ,the fish of the ,mediterranean1 a warm sea1 are generally poor and scarce4 ,fish taken in the cold waters between the ,american shore and the ,gulf ,stream are much esteemed2 while in and on the other side of the stream they are said to be tasteless1 and of no flavour4 ,between the coasts of ,china and the warm waters of the ,japanese current1 the seas abound with excellent fish2 but in the warm waters of the current and beyond1 they are never seen in such shoals4 ,in fact1 it is clearly ascertained that fishes are adapted to climates1 like birds and beasts4 ,it has been even affirmed1 after careful investigation1 that herrings1 which abound in the ,british ,seas1 and form a most important branch of our fisheries1 can only be found in a temperature varying from #ed deg4 to #eh deg4 ,hence the thermometer1 if brought into use by the fishermen1 would guide them to the spots where they may with the best chance cast their nets on dark nights1 when other indications are not perceptible4 ,this thermometer in its metallic case is perfectly suited for dipping overboard1 or placing in a bucket of water just taken from the sea1 to ascertain its temperature4 ,,chapter ,,vii4 ,,self-,,registering ,,thermometers4 #fi4 ,importance of ,self-,registering ,thermometers4--,heat being apparently the most effective agent in producing meteorological phenomena1 the determination of the highest temperature of the day1 and the lowest during the night1 is a prime essential to enable an estimate of the climate of any place to be formed4 ,to observe these extremes by means of the ordinary thermometer would be impracticable1 from the constant watchfulness which would be necessary4 ,hence1 the utility and importance of self-recording thermometers are evident4 ,a thermometer constructed to register the highest temperature is usually called a maximum thermometer2 one to show the lowest temperature is termed a minimum thermometer2 and if made to record both extremes of temperature1 it is designated a maximum-and-minimum thermometer4 ,we will1 for the sake of method1 describe the instruments in use in this order4 ,it would carry us beyond our scope to explain in detail the methods of dealing with temperature observations2 but we may remark that half the sum of the maximum and minimum temperature of each day of twenty-four hours1 is not what meteorologists designate the mean daily temperature1 although it very frequently approximates to it4 ,the mean temperature of the day is understood to be the average of twenty-four consecutive hourly readings of a thermometer2 and meteorology now supplies formulae whereby this result can be deduced from two or three observations only in a day4 ,but we would observe that the actual mean temperature of any place has not such an important influence upon life1 either animal or vegetable1 as the abruptness and magnitude of the variations of temperature4 ,climate1 therefore1 should be estimated more by the range of the thermometer than by the average of its indications4 ,the ,registrar ,general's returns prove that with a wide range of the thermometer1 the mortality greatly increases2 and it is now becoming apparent to meteorologists that the daily range of the thermometer marks the effects of temperature on the health of men1 and the success of crops1 better than any other meteorological fact of which we take cognizance4 ,now that self-registering thermometers are constructed with mercury1 the most appropriate of all thermometric substances1 not only for maxima1 but likewise for minima temperatures1 the determination of the diurnal range of temperature is rendered more certain1 and observations at different places are more strictly comparable4 ,,maxima ,,thermometers4 #gj4 ,rutherford's ,maximum ,thermometer4--,the maximum thermometer1 invented by ,dr4 ,john ,rutherford1 differs from an ordinary thermometer in having a small cylinder of steel1 porcelain1 or aluminium1 moving freely in the tube beyond the mercury1 so as to form an index4 ,the stem of the thermometer is fixed horizontally on the frame1 which must be suspended in the same position1 as represented in fig4 #ec4 ,the instrument is set by holding it bulb downward1 so as to allow the index to fall by its own gravity into contact with the mercury4 ,increase of heat produces expansion of the mercury1 which consequently pushes forward the index4 ,when the temperature decreases1 the mercury recedes from the index1 leaving it so that the extremity which was in contact with the mercury indicates upon the scale the highest temperature since the instrument was last set4 ,illustration3 ,fig4 #ec4 ,as it is easily constructed and is comparatively cheap1 it is still employed for ordinary purposes4 ,its disadvantages are1 firstly1 its liability of soon getting out of order by the index becoming embedded in the mercury1 or fixed by oxidation1 thus rendering it altogether useless2 secondly1 the ease with which the index can be displaced by the wind moving the instrument1 or other accidental disturbance1 so as to cause it to give erroneous indications occasionally2 and thirdly1 its consequent total unfitness for use at sea4 ,in the part of the tube beyond the mercury1 a small quantity of air is enclosed for the purpose of preventing the metal flowing freely in the tube4 ,this necessitates the construction of a larger bulb1 which renders the thermometer less sensitive4 ,moreover1 as it frequently happens that some mercury passes the index1 particles of air insinuate themselves in the metal1 and cause separations in the column1 which very often can be removed only by a maker4 ,to facilitate this re-adjustment1 a small chamber is left at the end of the tube1 and the mercury being expanded into it by heat until the index and air bubbles are forced into it1 if possible1 upon the cooling down again1 by a little management1 the mercury will contract1 leaving the air and index behind4 ,yet sometimes the index cannot be moved in the least from its place of fixture1 so that the instrument must be virtually reconstructed4 #ga4 ,phillip's ,maximum ,thermometer4--,a maximum thermometer1 better perhaps in its action than ,rutherford's1 has been suggested by ,professor ,john ,phillips1 of ,oxford4 ,a small portion of air is introduced into an ordinary thermometer1 so as to cut off about half an inch of the mercurial thread near its end in the tube4 ,this forms a maximum thermometer1 when the stem is arranged horizontally4 ,the isolated portion is pushed forward by expansion1 and is left in this position when the mercury contracts4 ,the end remote from the bulb shows on the scale the maximum temperature4 ,when made with a capillary tube so fine that the attraction arising from capillarity overcomes the force of gravity1 and prevents the mercury falling to the end of the tube when the instrument is inverted1 it forms a very serviceable thermometer1 quite portable and suitable for use on board ship4 ,in such a tube a smart shake from a swing of the hand is required to bring the detached portion back to the column1 so as to set the instrument for future observation2 no ordinary motion will move it4 ,when the thermometer has not this peculiarity1 the mercury will flow to the end1 if held bulb downward2 and in this state it is not at all a satisfactory instrument1 as the air is likely to be displaced1 and a great deal of tact is requisite to again get it to divide the column suitably4 ,it has been found in practice that the air bubble at different temperatures assumes different lengths1 and if very small it disappears in a few years by oxidation and by diffusion with the mercury1 so that the instrument becomes defective and uncertain in action1--results which led to the construction of the self-registering mercurial maximum thermometer1 invented and patented by ,messrs4 ,negretti and ,zambra4 ,it has been before the public about twelve years2 we may therefore1 now1 safely speak of its merits4 #gb4 ,negretti and ,zambra's ,patent ,maximum ,thermometer consists of a glass tube containing mercury fitted on an engraved scale1 as shown in fig4 #ed4 ,the part of the thermometer tube above the mercury is entirely free from air2 and at the point ,a in the bend above the bulb1 is inserted and fixed with the blow-pipe a small piece of solid glass1 or enamel1 which acts as a valve1 allowing mercury to pass on one side of it when heat is applied1 but not allowing it to return when the thermometer cools4 ,when mercury has been once made to pass the contraction1 which nothing but the expansive force of heat can effect1 and has risen in the tube1 the upper end of the column registers the maximum temperature4 ,to return the mercury to the bulb1 we must apply a force equal to that which raised it in the tube2 the force employed is gravity1 assisted when necessary by a little agitation of the instrument4 ,illustration3 ,fig4 #ed4 ,the degrees are generally divided on the stems of these thermometers1 but their frames of course bear a scale as well4 ,the makers have various styles of framing in wood1 metal1 porcelain1 and even glass4 ,each material is eligible according to requirements4 ,porcelain scales1 having the marks etched upon them by acid and permanently blackened and baked in1--by a process for which the inventors have a separate patent1--will be found very serviceable1 as they do not corrode or tarnish by exposure to any kind of weather2 while any amount of dust and dirt can readily be cleaned off4 ,the chief recommendation of this thermometer is its simplicity of construction1 enabling it to be used with confidence and safety4 ,of no other maximum thermometer can it be said that it is impossible to derange or put it out of order2 hence1 as regards durability1 it surpasses all others4 ,nothing short of actual breakage can cause it to fail4 ,hence it is the most easily portable of all self-registering thermometers1 an advantage which renders it suitable for travellers1 and for transmission abroad4 ,in the year #aheb1 the ,british ,meteorological ,society reported this thermometer to be the best which has yet been constructed for maximum temperature1 and particularly for sun observations4 ,since then eleven years have elapsed1 and it is still without a rival4 ,directions for use4 ,in using this thermometer for meteorological observations1 it should be suspended by means of two brass plates ,b1 ,c1 attached for that purpose1 in such manner that it hangs raised up a little at ,c1 and so placed that it is in the shade1 with the air passing freely to it from all sides2 then1 on an increase of heat1 the mercury will pass up the tube as in an ordinary thermometer1 and continue doing so as long as the heat increases4 ,on a decrease of heat1 the contraction of mercury will take place below the bend in the tube1 leaving the whole column of mercury in the tube1 thus registering the highest temperature1 and showing such till the instrument is disturbed4 ,to prepare the instrument for future observations1 remove and hold it perpendicularly1 with the bulb downward1 and then shake it4 ,the mercury will then descend in the tube1 and indicate the temperature of the air at that time2 and1 when again suspended1 is prepared for future observation4 ,after the temperature has attained a maximum1 there will be1 with a decrease of heat1 a slight contraction of mercury in the tube--as well as of that in the bulb--and hence doubts have arisen as to the accuracy of the registration2 but calculation shows1 and critical trial has proved1 that the greatest daily range of temperature will not produce an error large enough to be appreciable on the scale4 ,a very great advantage of this thermometer is that the mercury may be allowed to flow to the end of the tube without the maximum temperature attained during an experiment being lost4 ,it can be employed with the bulb uppermost4 ,all that is necessary for reading the maximum temperature is to slope the instrument so that the mercury flows gently towards the bulb4 ,it will then stop at the contraction so as to show the maximum temperature on the scale4 ,afterwards the mercury is driven into the bulb by agitating the instrument while held in the hand4 ,hence the instrument is invaluable as a registering thermometer on board ship1 as its indications are in no way affected by the motions and tremors of the vessel4 ,for physiological experiments1 such as taking the temperature of the mouth in fever1 this thermometer is the only one that can be used with certainty1 as it can be held in any position1 without losing the maximum temperature attained4 ,,minima ,,thermometers4 #gc4 ,rutherford's ,alcohol ,minimum ,thermometer1 fig4 #ee1 consists of a glass tube1 the bulb and part of the bore of which is filled with perfectly pure spirits of wine1 in which moves freely a black glass index4 ,a slight elevation of the thermometer1 bulb uppermost1 will cause the glass index to flow to the surface of the liquid1 where it will remain1 unless violently shaken4 ,on a decrease of temperature the alcohol recedes1 taking with it the glass index2 on an increase of temperature the alcohol alone ascends in the tube1 leaving the end of the index farthest from the bulb indicating the minimum temperature4 ,illustration3 ,fig4 #ee4 ,directions for using1 c4--,having caused the glass index to flow to the end of the column of spirit1 by slightly tilting the thermometer1 bulb uppermost1 suspend the instrument 7in the shade with the air passing freely to it on all sides7 by the two brass plates attached for that purpose1--in such manner that the bulb is about half an inch lower than the upper1 or the end of the thermometer farthest from the bulb2 then1 on a decrease of temperature1 the spirits of wine will descend1 carrying with it the glass index2 on an increase of temperature1 however1 the spirits of wine will ascend in the tube1 leaving that end of the small glass index farthest from the bulb indicating the minimum temperature4 ,to reset the instrument1 simply raise the bulb end of the thermometer a little1 as before observed1 and the index will again descend to the end of the column1 ready for future observation4 ,precautions4--#a4 ,by no means jerk or shake an alcohol minimum thermometer when resetting it1 for by so doing it is liable to disarrange the instrument1 either by causing the index to leave the spirit1 or by separating a portion of the spirit from the main column4 #b4 ,as alcohol thermometers have a tendency to read lower by age1 owing to the volatile nature of the fluid allowing particles in the form of vapour to rise and lodge in the tube1 it becomes necessary to compare them occasionally with a mercurial thermometer whose index error is known2 and if the difference be more than a few tenths of a degree1 examine well the upper part of the tube to see if any alcohol is hanging in the bore thereof2 if so1 the detached portion of it can be joined to the main column by swinging the thermometer with a pendulous motion1 bulb downwards4 #c4 ,the spirit column is sometimes much separated by jolting in travelling4 ,if the instrument is in such a condition when received1 it should be held by the right hand1 bulb downward1 and the frame tapped smartly1 but cautiously1 against the palm of the left hand4 ,the broken thread of spirit will soon begin to join1 and by continuing the operation a sufficient time all the bubbles will disappear1 and the thermometer become as good as ever4 #gd4 ,horticultural ,minimum ,thermometer4--,this instrument1 represented in fig4 #ef1 is a special construction of ,rutherford's minimum thermometer to meet the requirements of horticulturists4 ,it is desirable1 if not essential1 that gardeners should have the means of ascertaining to what temperature stoves and greenhouses descend on cold nights1 especially in winter4 ,this thermometer is mounted on a strong cast zinc frame1 with the divisions and figures of the scale raised4 ,illustration3 ,fig4 #ef4 ,the sunk surface of the frame is painted dark2 the figures and division a bright colour1 so that observations can be made without a close inspection of the instrument4 ,the directions for using are the same as those given in the preceding section4 ,it may be used as an ordinary thermometer1 by simply hanging it from the top loop1 in which position1 the coloured liquid will always indicate the present temperature4 ,it was a source of annoyance with the ordinary boxwood and flat metal scales1 that after a time1 exposure to a damp warm atmosphere favoured the growth of confervae upon them1 and obliterated the divisions2 the plan of raising the figures and divisions of the scale has been found to prevent the destruction of the instrument in this way4 #ge4 ,baudin's ,alcohol ,minimum ,thermometer4--,this instrument resembles ,rutherford's thermometer in appearance2 its indications are given by the expansion and contraction of alcohol1 and its minimum temperature is likewise registered by a glass index being pulled back and left behind by the alcohol1 as in ,rutherford's instrument4 ,there is1 however1 a great improvement in ,baudin's instrument2 for whilst ,rutherford's thermometer can only register in a horizontal position1 ,baudin's can be used either horizontally or vertically1 as necessity may require4 ,this important change is effected in the following manner3--,instead of the index in the thermometer being loose and free to run up and down according to the position in which the instrument is held1 as in ,rutherford's1 the index in the new instrument is made to fit the bore of the tube as nearly tight as possible1 so much so that in holding the thermometer even upside down1 or shaking it1 the index will not shift from its position2 but1 inasmuch as a minimum thermometer with an immoveable index could not be set when required for observation1 and would consequently be useless1 the inventor has introduced behind the index a piece of solid glass1 about one-and-a-half inch in length1 which moves freely in the alcohol4 ,the addition of the weight of this piece of glass on the top of the index1 when turned upside down1 forces the index down to the edge of the alcohol2 and it is there left1 as in the case of the ordinary ,rutherford's thermometer4 ,it is1 therefore1 by turning the thermometer upside down1 and letting the moveable piece of glass fall on the index1 that the index is driven to the end of the alcohol2 after this operation the thermometer is hung up either horizontally or vertically1 and will then be ready for use4 ,the index1 although immoveable per se1 is by the alcohol drawn back1 as in the ordinary minimum1 and its indications are read off on the scale from the top of the index4 #gf4 ,mercurial ,minima ,thermometers desirable4--,alcohol does not expand equally for equal increments of heat1 consequently errors are likely to exist in the scale indications unless the graduations are very accurately--not necessarily equally--made4 ,on this account1 as well as from the volatility of alcohol1 and the intervention of gaseous partitions in the tube1 a good and thoroughly reliable minimum thermometer was for a long time a desideratum4 ,it was desirable to obtain a thermometer which should register the lowest temperature by mercury1 the fluid in general use for meteorological thermometers4 ,several instruments have recently been invented to meet this requirement1 which are suitable and satisfactory for land purposes1 but one well adapted for use on board ship is still very much wanted4 ,for very low temperatures1 alcohol thermometers will always be required2 as mercury freezes at -#dj deg4 ,f1 and contracts very irregularly much before this point1 while alcohol has never yet been frozen4 #gg4 ,negretti and ,zambra's ,patent ,mercurial ,minimum ,thermometer1 represented by fig4 #eg1 has a cylindrical bulb of large size1 which1 at first sight1 might induce the idea that the instrument would not be sufficiently sensitive2 but as length is given to the cylinder instead of increasing its diameter1 it will be found as sensitive as a globular bulb of the same diameter1 and much more so than an ordinary alcohol thermometer4 ,illustration3 ,fig4 #eg4 ,the reason for having the bulb large is to allow the internal diameter of the thermometer tube to be larger than that generally used for thermometrical purposes1 so that a steel index1 pointed at both ends1 may move freely within when required4 ,the tube is blown1 filled and regulated in the usual way1 #fj deg4 of temperature being about half-way up the tube4 ,a small cylindrical bulb is then formed at the upper end of the tube1 and then is introduced a steel needle pointed at both ends1 that in contact with the mercury being abrupt1 the other more prolonged4 ,the open extremity of the tube is now drawn out into a fine capillary tube1 and the bulb of the instrument warmed so as to cause the mercury to fill the tube completely4 ,when the mercury reaches the capillary tube1 the flame of a blow-pipe is applied2 the glass is dexterously melted1 the superfluous part taken away1 and the tube left hermetically closed4 ,during this operation1 the steel index has been embedded in the heated mercury4 ,as the instrument cools1 if held upright1 the mercury will recede and expose the needle1 which will then follow the descending column simply by its own gravity4 ,in this condition the thermometer resembles ,rutherford's maximum1 being a tube of mercury with a steel index floating on its surface2 but it possesses these important advantages3 it is quite free from air1 so that the mercury can move with perfect freedom2 and the index is pointed at both ends1 to allow the mercury to pass1 instead of being ground flat to prevent it4 ,to use the ,thermometer1 it is suspended perpendicularly 7figure #eg7 with the steel index resting on the surface of the mercurial column4 ,as the mercury in the cylinder contracts1 that in the tube descends1 and the index1 of its own gravity1 follows it2 on the contrary1 as the mercury expands and rises in the tube1 it passes the index on one side1 and in rising1 exerts a lateral pressure on the needle1 and jams it to one side of the tube1 where it remains firmly fixed1 leaving the upper point of the needle indicating the minimum temperature4 ,in this thermometer1 the reading is always from the upper point of the needle1 and not from the mercury itself4 ,to extricate the ,needle from the mercury1 a magnet is used1 when1 if the needle is embedded only a few degrees1 it can readily be withdrawn without altering the position of the instrument4 ,should the magnet not be sufficient for the purpose1 we simply turn the thermometer on its support from the upright position1 slightly elevating the bulb 7fig4 #eh 7#b774 ,the mercury and index will then flow into the small reservoir4 ,should the index not freely leave the tube with the mercury1 assist it with a magnet1 and when the mercury and index are in the upper bulb 7figure #b71 apply a magnet outside1 which will attract and hold fast the index2 and whilst thus holding it1 again bring the thermometer to the upright position1 when the mercury will immediately fall back into the tube1 leaving the index attached to the magnet 7figure #d71 with which it is guided down to the surface of the mercury1 ready for another observation4 ,illustration3 ,fig4 #eh4 ,care must be taken not to withdraw the magnet until the index is in contact with mercury2 for1 if released before touching1 it might plunge too deeply1 and give a false indication4 ,the rule for re-setting it will be to bring the needle-point in contact with the mercury1 and then withdraw the magnet1 having previously ascertained that no particles of mercury are attached to the index4 ,it may sometimes1 though rarely1 happen1 that from the time a minimum temperature is registered by the index1 and by the time an observation is made1 the mercury may have risen so high in the tube as to completely pass the index1 as shown 7figure #c74 ,should it so happen1 the space which the index occupies will readily be observed1 as it will be pressed to one side of the tube1 causing a different appearance in that part1 although the point of the needle may not be seen4 ,if such be the case1 apply a magnet to the spot where you see the index is fixed3 this will hold the needle firmly4 ,then1 by slightly tilting the thermometer bulb uppermost1 the mercury will flow into the top bulb1 leaving the index attached to the magnet1 and quite uncovered4 ,having taken the reading1 draw the needle into the top bulb1 and hold it there whilst you adjust the thermometer by again bringing it to the upright position4 ,by contracting the bore of this thermometer1 at the bend of the tube1 sufficiently to keep the mercury from flowing out of its bulb with too much freedom by motion1 the instrument becomes perfectly safe for transmission abroad4 #gh4 ,negretti ,zambra's ,second ,patent ,mercurial ,minimum ,thermometer4--,in this thermometer a principle is used that has been long known to scientific men1 viz4 the affinity of mercury for platinum4 ,if mercury be placed in contact with platinum under ordinary circumstances1 no effect will take place2 but if the mercury is once made to attack the platinum1 the amalgamation is permanent and the contact perfect1 so much so1 that the principle was made use of in constructing standard barometers4 ,a ring of platinum was fused round the end of the tube1 dipping into the mercury2 and the contact between the platinum and mercury became so perfect that air could not creep down the tube and up the bore1 as in ordinary barometer tubes4 ,this principle of adhesion or affinity of mercury for platinum has been brought into play for the purpose of arresting the mercury after it has reached the minimum temperature in a thermometer4 ,this thermometer is made as follows3--behind the bulb is placed a supplementary chamber2 in the space or neck between the bulb of the thermometer and the chamber1 is placed a small piece of platinum2 this may be of any shape or size1 but the smaller the better4 ,this is not to fit in the neck2 it must1 on the contrary1 be rather loose2 it may be fastened in position or not4 ,the instrument is represented by fig4 #ei4 ,illustration3 ,fig4 #ei4 ,directions for using4--,having suspended the thermometer in a horizontal position1 the mercury is made to stand in exact contact with the platinum plug by slightly elevating the bulb end of the instrument4 ,the thermometer is now ready for observation4 ,on a decrease of temperature1 the mercury will endeavour to contract first from the easier passage1 viz4 behind the bulb2 but in consequence of the adhesion of the mercury to the platinum1 it cannot recede from here1 it is therefore forced to contract from the indicating tube1 and will continue to do so as long as the temperature decreases2 and as no indices are employed in this thermometer1 the extreme end of the mercurial column will show how cold it has been4 ,on an increase of temperature the mercury will glide over the platinum plug and expand by the easier passage into the supplementary chamber1 and there remain until a decrease of temperature again takes place1 when the mercury that had gone into the supplementary chamber will be the first to recede1 until it reaches the platinum plug1 its further progress being arrested2 it will then fall in the indicating tube1 and there remain until re-set4 #gi4 ,casella's ,mercurial ,minimum ,thermometer4--,the general form and arrangement of this instrument is shown in fig4 #fj4 ,a tube with large bore1 a1 has at the end a flat glass diaphragm formed by the abrupt junction of a small chamber1 b c1 the inlet to which at b is larger than the bore of the indicating tube4 ,the result of this is that on setting the thermometer1 as described below1 the contracting force of the mercury in cooling withdraws the fluid in the indicating stem only2 whilst on its expanding with heat1 the long column does not move1 the increased bulk of mercury finding an easier passage into the small pear-shaped chamber attached4 ,illustration3 ,fig4 #fj4 ,we believe that a small speck of air must be confined in the chamber1 b c1 to act as a spring to start the mercury from the chamber in the act of setting the thermometer4 ,were this air not present1 the mercury would so adhere to the glass that no amount of shaking could induce it to flow from the chamber4 ,to set the ,instrument1 place it in a horizontal position1 with the back plate1 d1 suspended on a nail1 and the lower part supported on a hook1 e4 ,the bulb end may now be gently raised or lowered1 causing the mercury to flow slowly until the bent part1 a1 is full and the chamber1 b c1 quite empty4 ,at this point the flow of mercury in the long stem of the tube is arrested1 and indicates the exact temperature of the bulb or air at the time4 ,on an increase of temperature the mercury will expand into the small chamber1 b c2 and a return of cold will cause its recession from this chamber only1 until it reaches the diaphragm1 b4 ,any further diminution of heat withdraws the mercury down the bore to whatever degree the cold may attain1 where it remains until farther withdrawn by increased cold1 or till re-set for future observation4 ,,maxima ,,and ,,minima ,,thermometers4 #hj4 ,rutherford's arrangement for obtaining a complete instrument for the registration of heat and cold was simply mounting a maximum thermometer and a minimum thermometer upon the same frame or slab4 ,thus constructed1 they are often called day and night thermometers1 though somewhat inappropriately2 for in temperate climates the temperature of the night sometimes exceeds that of the day1 notwithstanding the reverse is the general law of temperature4 ,fig4 #fa will explain the arrangement of ,rutherford's day and night thermometer4 ,illustration3 ,fig4 #fa4 #ha4 ,sixe's ,self-,registering ,thermometer4--,the very ingenious and certainly elegant instrument about to be described was invented by ,james ,sixe1 of ,colchester4 ,it consists of a long cylindrical bulb1 united to a tube of more than twice its length1 bent round each side of it in the form of a syphon1 and terminated in a smaller1 oval-shaped bulb4 ,figure #fb gives a representation of this instrument4 ,the lower portion of the syphon is filled with mercury2 the long bulb1 the other parts of the tube1 and part of the small bulb1 with highly rectified alcohol4 ,a steel index moves in the spirit in each limb of the syphon4 ,the two indices are terminated at top and bottom with a bead of glass1 to enable them to move with the least possible friction1 and without causing separation of the spirit1 or allowing mercury to pass easily4 ,they would1 from their weight1 always rest upon the mercury2 but each has a fine hair tied to its upper extremity and bent against the interior of the tube1 which acts as a spring with sufficient elasticity to keep the index supported in the spirit in opposition to gravity4 ,illustration3 ,fig4 #fb4 ,the instrument acts as follows3--,a rise of temperature causes the spirit in the long bulb to expand and press some of the mercury into the other limb of the syphon1 into which it rises also from its own expansion1 and carries the index with it1 until the greatest temperature is attained4 ,the lower end of this index then indicates upon the engraved scale the maximum temperature4 ,as the temperature falls the spirit and the mercury contract1 and in returning towards the bulb the second index is met and carried up by the mercury until the lowest temperature occurs1 when it is left to indicate upon the scale the minimum temperature4 ,the limb of the syphon adjoining the bulb requires1 therefore1 a descending scale of thermometric degrees2 the other limb1 an ascending scale4 ,the graduations must be obtained by comparisons with a standard thermometer under artificial temperatures1 which should be done in this way for every #e deg41 in order to correct for the inequality in the bore of the tube1 and the irregular expansion of the spirit4 ,the instrument is set for observation by bringing the indices into contact with the mercury1 by means of a small magnet1 which attracts the steel through the glass1 so that it is readily drawn up or down4 ,they should be drawn nearly to the top of the limbs when it is desired to remove the instrument1 which should be carefully carried in the vertical position2 for should it be inverted1 or laid flat1 the spirit may get among the mercury1 and so break up the column as to require the skill of a maker to put it in order again4 ,for transmission by ordinary conveyances1 it requires that attention be given to keep it vertical4 ,the entanglement of a small portion of mercury with the indices is sometimes a source of annoyance in this instrument1 for the readings are thereby rendered somewhat incorrect4 ,small breakages in the mercury1 either from intervening bubbles of spirit or adhesion to the indices1 may generally be rectified by cautiously tapping the frame of the instrument1 so as to cause the mercury to unite by the assistance thus given to its superior gravity4 ,these thermometers1 when carefully made and adjusted to a standard thermometer1 are strongly recommended for ordinary purposes1 where strict scientific accuracy is not required4 ,this is also the only fluid thermometer applicable for determining the temperature of the sea at depths4 ,,chapter ,,viii4 ,,radiation ,,thermometers4 #hb4 ,solar and ,terrestrial ,radiation considered4--,the surface of the earth absorbs the heat of the sun during the day1 and radiates heat into space during the night4 ,the envelope of gases and vapour1 which we call the atmosphere1 exerts highly important functions upon these processes4 ,thanks to the researches of ,professor ,tyndall1 we are now enabled to understand these functions much more clearly than heretofore4 ,his elaborate1 patient1 and remarkably sagacious series of experiments upon radiant heat1 have satisfactorily demonstrated that dry air is as transparent to radiant heat as the vacuum itself2 while air perfectly saturated with aqueous vapour absorbs more than five per cent4 of radiant heat1 estimated by the thermal unit adopted for the galvanometer indications of the effect upon a thermo-electric pile4 ,aqueous vapour1 in the form of fog or mist1 as is well known1 gives to our sensation a feeling of cold1 and interferes with the healthy action of the skin and the lungs2 the cause being its property of absorbing heat from our person4 ,air containing moisture in an invisible state likewise exerts a remarkable influence in radiating and absorbing heat4 ,by reason of these properties1 aqueous vapour acts as a kind of blanket upon the ground1 and maintains upon it a higher temperature than it would otherwise have4 ,regarding the earth as a source of heat1 no doubt at least ten per cent4 of its heat is intercepted within ten feet of the surface4 ,thus vapour--whether transparent and invisible1 or visible1 as cloud1 fog1 or mist--is intimately connected with the important operations of solar and terrestrial radiation4 ,cloudy1 or humid days1 diminish the effect upon the soil of solar radiation2 similar nights retard the radiation from the earth4 ,a dry atmosphere is the most favourable for the direct transmission of the sun's rays2 and the withdrawal of the sun from any region over which the air is dry1 must be followed by very rapid cooling of the soil4 ,the removal1 for a single summer night1 of the aqueous vapour from the atmosphere which covers ,england1 would be attended by the destruction of every plant which a freezing temperature could kill4 ,in ,sahara1 where 'the soil is fire and the wind is flame1' the refrigeration at night is often painful to bear4 ,ice has been formed in this region at night4 ,in ,australia1 also1 the diurnal range of temperature is very great1 amounting1 commonly1 to between #dj and #ej degrees4 ,in short1 it may be safely predicted1 that wherever the air is dry1 the daily thermometric range will be great4 ,this1 however1 is quite different from saying that when the air is clear1 the thermometric range will be great4 ,great clearness to light is perfectly compatible with great opacity to heat2 the atmosphere may be charged with aqueous vapour while a deep blue sky is overhead2 and on such occasions the terrestrial radiation would1 notwithstanding the 'clearness1' be intercepted4 ,the great range of the thermometer is attributable to the absence of that protection against gain or loss of heat which is afforded when aqueous vapour is present in the air2 and during such weather the rapid abstraction of moisture from the surface of plants and animals is very deleterious to their healthy condition4 ,the nipping of tender plants by frost1 even when the air of the garden is some degrees above the freezing temperature1 is also to be referred to chilling by radiation4 ,hence the practice of gardeners of spreading thin mats1 of bad radiating material1 over tender plants1 is often attended with great benefit4 ,by means of the process of terrestrial radiation ice is artificially formed in ,bengal1 where the substance is never formed naturally4 ,shallow pits are dug1 which are partially filled with straw1 and on the straw flat pans containing water which had been boiled is exposed to the clear firmament4 ,the water is a very powerful radiant1 and sends off its heat into space4 ,the heat thus lost cannot be supplied from the earth--this source being cut off by the non-conducting straw4 ,before sunrise a cake of ice is formed in each vessel4444 ,to produce the ice in abundance1 the atmosphere must not only be clear1 but it must be comparatively free from aqueous vapour4 ,considering1 therefore1 the important consequences attending both terrestrial and solar radiation1 it appears to us that observations from radiation thermometers are of much more utility in judging of climate than is usually supposed4 ,these observations are very scanty2 and what few are upon record are not very reliable1 principally from bad exposure of the instruments1 while the want of uniformity in construction may be another cause4 ,herschell's actinometer and ,pouillet's pyrheliometer1 instruments for ascertaining the absolute heating effect of the sun's rays1 should1 however1 be more generally employed by meteorologists4 ,in comparing observations on radiation it should be kept in mind1 that the difference between a thermometer which1 properly confined or shaded1 gives the true temperature of the night air1 and one which is permitted to radiate freely towards space1 must be greater at high elevations than at low ones2#f because the higher the place1 the less the thickness of the vapour-screen to intercept the radiation4 #hc4 ,solar ,radiation ,thermometer4--,as the interchange of heat between two bodies by radiation depends upon the relative temperature which they respectively possess1 the earth1 by the rays transmitted from the sun during the day1 must be continually gaining an accession of heat1 which would be far from being counterbalanced by the opposite effect of its own radiation into space4 ,hence1 from sunrise till two or three hours after mid-day1 the earth goes on gradually increasing in temperature1 the augmentation being greatest where the surface consists of materials calculated1 from their colour and texture1 to absorb heat1 and where it is deficient in moisture1 which1 by its evaporation1 would have a tendency to diminish it4#g ,it is1 therefore1 important to have instruments for measuring the efficacy of solar radiation1 apart from those for exhibiting the temperature of the place in the shade4 ,illustration3 ,fig4 #fc4 ,fig4 #fc shows the arrangement of ,negretti ,zambra's maximum thermometer1 for registering the greatest heat of the sun's direct rays1 hence called a solar radiation thermometer4 ,it has a blackened bulb1 the scale divided on its own stem1 and the divisions protected by a glass shield4 ,in use it should be placed nearly horizontally1 resting on ,y supports of wood or metal1 with its bulb in the full rays of the sun1 resting on grass1 and1 if possible1 so that lateral winds should not strike the bulb2 and at a sufficient distance from any wall1 so that it does not receive any reflected heat from the sun4 ,some observers place the thermometer as much as two feet from the ground4 ,it would be very desirable if one uniform plan could be recognized3 that of placing the instrument as indicated in the figure appears to be most generally adopted1 and the least objectionable4 #hd4 ,vacuum ,solar ,radiation ,thermometer4--,in order that the heat absorbed by the blackened bulb of the solar radiation thermometer may not in part be carried off by the currents of air which would come into contact with it1 the instrument has been improved by ,messrs4 ,negretti and ,zambra into the vacuum solar radiation thermometer1 as illustrated by fig4 #fd4 ,illustration3 ,fig4 #fd4 ,this consists of a blackened-bulb radiation thermometer1 enclosed in a glass tube and globe1 from which all air is exhausted4 ,thus protected from the loss of heat which would ensue if the bulb were exposed1 its indications are from #bj deg4 to #cj deg4 higher than when placed side by side with a similar instrument with the bulb exposed to the passing air4 ,at times when the air has been in rapid motion1 the difference between the reading of a thermometer giving the true temperature of the air in the shade1 and an ordinary solar radiation thermometer1 has been #bj deg4 only1 whilst the difference between the air temperature and the reading of a radiation thermometer in vacuo has been as large as #ej deg4 ,it is also found that the readings are almost identical at distances from the earth varying from six inches to eighteen inches4 ,by the use of this improvement1 it is hoped that the amounts of solar radiation at different places may be rendered comparable2 hitherto they have not been so2 the results found at different places cannot be compared1 as the bulbs of the thermometers are under very different circumstances as to exposure and currents of air4 ,important results are anticipated from this arrangement4 ,the observations at different places are expected to present more agreement4 ,observers would do well to note carefully the effect of any remarkable degree of intensity in the solar heat upon particular plants1 crops1 fruit or other trees4 #he4 ,terrestrial ,radiation ,thermometer is an alcohol minimum thermometer1 with the graduations etched upon the stem1 and protected by a glass shield1 as shown in figure #fe1 instead of being mounted on a frame4 ,the bulb is transparent2 that is to say1 the spirit is not coloured4 ,illustration3 ,fig4 #fe4 ,in use1 it should be placed with its bulb fully exposed to the sky1 resting on grass1 the stem being supported by little forks of wood4 ,the precautions required with this thermometer are similar to those for ordinary spirit thermometers1 explained at page #gf4 ,illustration3 ,fig4 #ff4 #hf4 ,a,ethrioscope4--,the celebrated experimental philosopher1 ,sir ,john ,leslie1 was the inventor of this instrument1 the purpose of which is to give a comparative idea of the radiation proceeding from the surface of the earth towards the sky4 ,it consists1 as represented in fig4 #ff1 of two glass bulbs united by a vertical glass tube1 of so fine a bore that a little coloured liquid is supported in it by its own adhesion1 there being air confined in each of the bulbs4 ,the bulb1 ,a1 is enclosed in a highly polished brass sphere1 ,d1 made in halves and screwed together4 ,the bulb1 ,b1 is blackened and placed in the centre of a metallic cup1 ,c1 which is well gilt on the inside1 and which may be covered by a top1 ,f4 ,the brass coverings defend both bulbs from solar radiation1 or any adventitious source of heat4 ,when the top is on1 the liquid remains at zero of the scale4 ,on removing the top and presenting the instrument to a clear sky1 either by night or by day1 the bulb1 ,b1 is cooled by terrestrial radiation1 while the bulb1 ,a1 retains the temperature of the air4 ,the air confined in ,b1 therefore1 contracts2 and the elasticity of that within ,a forces the liquid up the tube1 to a height proportionate to the intensity of the radiation4 ,such is the sensitiveness of the instrument1 that the smallest cloud passing over it checks the rise of the liquid4 ,sir ,john ,leslie says3--,under a clear blue sky1 the aethrioscope will sometimes indicate a cold of fifty millesimal degrees2 yet1 on other days1 when the air seems equally bright1 the effect is hardly #cj deg4 ,this anomaly1 according to ,dr4 ,tyndall1 is simply due to the difference in the quantity of aqueous vapour present in the atmosphere4 ,the presence of invisible vapour intercepts the radiation from the aethrioscope1 while its absence opens a door for the escape of this radiation into space4 #hg4 ,pouillet's ,pyrheliometer4--,this instrument is composed of a shallow cylinder of steel1 ,a1 fig4 #fg1 which is filled with mercury4 ,into the cylinder a thermometer1 ,d1 is introduced1 the stem of which is protected by a piece of brass tubing4 ,we thus obtain the temperature of the mercury4 ,the flat end of the cylinder is to be turned towards the sun1 and the surface1 ,b1 thus presented is coated with lamp black4 ,there is a collar and screw1 ,c1 by means of which the instrument may be attached to a stake driven into the ground1 or into the snow1 if the observations are made at considerable heights4 ,it is necessary that the surface which receives the sun's rays should be perpendicular to the rays2 and this is secured by appending to the brass tube which shields the stem of the thermometer1 a disk1 ,e1 of precisely the same diameter as the steel cylinder4 ,when the shadow of the cylinder accurately covers the disk1 we are sure that the rays fall1 as perpendiculars1 on the upturned surface of the cylinder4 ,illustration3 ,fig4 #fg4 ,the observations are made in the following manner3--,first1 the instrument is permitted1 not to receive the sun's rays1 but to radiate its own heat for five minutes against an unclouded part of the firmament2 the decrease of the temperature of the mercury consequent on this radiation is then noted4 ,next1 the instrument is turned towards the sun1 so that the solar rays fall perpendicularly upon it for five minutes2 the augmentation of heat is now noted4 ,finally1 the instrument is turned again towards the firmament1 away from the sun1 and allowed to radiate for another five minutes1 the sinking of the thermometer being noted as before4 ,in order to obtain the whole heating power of the sun1 we must add to his observed heating power the quantity lost during the time of exposure1 and this quantity is the mean of the first and last observations4 ,supposing the letter ,r to represent the augmentation of temperature by five minutes' exposure to the sun1 and that t and t#a represent the reductions of temperature observed before and after1 then the whole force of the sun1 which we may call ,t1 would be thus expressed3--,t ,r #a_/b7t t#a74 ,the surface on which the sun's rays here fall is known2 the quantity of mercury within the cylinder is also known2 hence we can express the effect of the sun's heat upon a given area1 by stating that it is competent1 in five minutes1 to raise so much mercury so many degrees in temperature4--,dr4 ,tyndall's ,heat considered as a ,mode of ,motion4 ,illustration3 ,fig4 #fh4 #hh4 ,sir ,john ,herschell's ,actinometer1 for ascertaining the absolute heating effect of the solar rays1 in which time is considered one of the elements of observation1 is illustrated by fig4 #fh4 ,the actinometer consists of a large cylindrical thermometer bulb1 with a scale considerably lengthened1 so that minute changes may be easily seen4 ,the bulb is of transparent glass filled with a deep blue liquid1 which is expanded when the rays of the sun fall direct on the bulb4 ,to take an observation1 the actinometer is placed in the shade for one minute and read off2 it is then exposed for one minute to sunshine1 and its indication recorded2 it is finally restored to the shade1 and its reading noted4 ,the mean of the two readings in the shade1 subtracted from that in the sun1 gives the actual amount of expansion of the liquid produced by the sun's rays in one minute of time4 ,for further information1 see ,report of the ,royal ,society on ,physics and ,meteorology2 or ,kaemtz's ,meteorology1 translated by ,c4 ,v4 ,walker2 or the ,admiralty ,manual of ,scientific ,instructions4 ,,chapter ,,ix4 ,,deep-,,sea ,,thermometers4 #hi4 ,on ,sixe's ,principle4--,thermometers for ascertaining the temperature of the sea at various depths are constructed to register either the maximum or minimum temperature1 or both4 ,the principle of each instrument is that of ,sixe4 ,there are very few parts of the ocean in which the temperature below is greater than at the surface1 except in the ,polar ,seas1 where it is generally found to be a few degrees warmer at considerable depths than at the surface4 ,when the instrument is required to register only one temperature1 it can be made narrower and more compact--a great advantage in sounding2 and with less length of bulb and glass tube1 so that the liability of error is diminished4 ,hence1 the minimum is the most generally useful for deep-sea soundings4 ,these thermometers must be sufficiently strong to withstand the pressure of the ocean at two or three miles of depth1 where there may be a force exerted to compress them exceeding three or four hundred atmospheres 7of #ae lbs4 to the square inch74 ,many have been the contrivances for obtaining correct deep-sea indications4 ,thermometers and machines of various sorts have been suggested1 adopted1 and eventually abandoned as only approximate instruments4 ,the principal reason for such instruments failing to give correct or reliable indications1 has been that the weight or pressure on the bulbs at great depths has interfered with the correct reading of the instruments4 ,thermometers have been enclosed in strong water-tight cases to resist the pressure2 but this contrivance has only had the tendency to retard the action1 so much so as to throw a doubt on the indications obtained by the instrument so constructed4 ,the thermometers constructed by ,messrs4 ,negretti and ,zambra for this purpose do not differ materially from those usually made under the denomination of ,sixe's thermometers1 except in the following most important particular3--,the usual ,sixe's thermometers have a central reservoir or cylinder containing alcohol2 this reservoir1 which is the only portion of the instrument likely to be affected by pressure1 has been1 in ,negretti and ,zambra's new instrument1 superseded by a strong outer cylinder of glass1 containing mercury and rarefied air2 by this means the portion of the instrument susceptible of compression1 has been so strengthened that no amount of pressure can possibly make the instrument vary4 ,this instrument has been tested in every possible manner1 and the results have been highly satisfactory1 so much so as to place their reliability beyond any possible doubt4 ,the scales are made of porcelain1 and are firmly secured to a back of oak1 which holds in a recess the bulb with its protecting shield1 and is rounded off so as to fit easily and firmly in a stout cylindrical copper case1 in which the thermometer is sent down when sounding 7see fig4 #fi74 ,the lid of the case is made to fit down closely1 and water-tight4 ,at the bottom of the case is a valve opening upward2 and the lid has a similar valve4 ,these allow the water to pass through the case as the instrument sinks1 so that the least amount of obstruction is offered to the descent4 ,at the lower end of the case is a stout brass spring1 to protect the instrument from a sudden jar if it should touch the bottom while descending rapidly4 ,as the instrument is drawn up1 the valves close with the weight of water upon them1 and it arrives at the surface filled with water brought up from its lowest position4 ,the deep-sea thermometers used in the ,royal ,navy are of this pattern4 ,illustration3 ,fig4 #fi4 #ij4 ,johnson's ,metallic ,deep-,sea ,thermometer4--,the objection to the employment of mercurial thermometers for ascertaining the temperature of the ocean at depths1 arising from the compression of the bulbs1 which was of such serious consequence previous to the modification made in the construction of the instrument by ,messrs4 ,negretti and ,zambra1 led to the construction of a metallic thermometer altogether free from liability of disturbance from compression by the surrounding water2 which1 however1 is certainly not so sensitive to changes of temperature as mercury4 ,this instrument is the invention of ,henry ,johnson1 ,esq41 ,f4,r4,a4,s41 and is thus described by him3-- ,during the year #ahdd some experiments were made by ,james ,glaisher1 ,esq41 ,f4,r4,s41 on the temperature of the water of the ,thames near ,greenwich at the different seasons of the year2 when that gentleman found that the indications of temperature were greatly affected by the pressure on the bulbs of the thermometers4 ,at a depth of #be feet this pressure would be nearly equal to the presence of three-fourths of an atmosphere4 ,these observations demonstrate the importance of using in deep-sea soundings an instrument free from liability of disturbance from compression by the surrounding water1 and have ultimately led to the construction of the thermometer now to be described4 ,the instrument is composed of solid metals of considerable specific gravity1 viz4 of brass and steel1 the specific gravity of these metals being #h4ci and #g4ha respectively4 ,they are therefore not liable to compression by the water1 which under a pressure of #a1abj atmospheres1 or at a depth of #e1jjj fathoms in round numbers1 acquires a density or specific gravity of #a4jf4 ,in the construction of this instrument1 advantage has been taken of the well-known difference in the ratios of expansion and contraction by heat and cold of brass and steel1 to form compound bars of thin bars of these metals riveted together2 and which will be found to assume a slight curve in one direction when heat has expanded the brass more than the steel1 and a slight one in the contrary direction when cold has contracted the brass more than the steel4 ,the indications of the instrument record the motions under changes of temperature of such compound bars2 in which the proportion of brass1 the more dilatable metal1 is two-thirds1 and of steel one-third4 ,illustration3 ,fig4 #gj4 ,upon one end of a narrow plate of metal about a foot long1 a1 are fixed three scales of temperature1 h1 which ascend from #be deg4 to #ajj deg4 ,f41 and which are shown more clearly in the drawing detached from the instrument4 ,upon one of these scales the present temperature is shown by the pointer1 e1 which turns upon a pivot in its centre4 ,the register index1 g1 to the maximum temperature1 and the index1 f1 to the minimum temperature1 are moved along the other scales by the pin upon the moving pointer1 at e1 where they are retained by stiff friction4 ,at equal distances from the centre of the pointer are two connecting pieces1 d d1 by which it is attached to the free ends of two compound bars1 b b1 and its movements correspond with the movements of the compound bars under variations of temperature4 ,the other ends of the bars are fastened by the plate1 c1 to the plate1 a1 on which the scales of temperature are fixed4 ,the connection of the bars with both sides of the centre of the pointer prevents disturbance of indication by lateral concussion4 ,the case of the instrument has been improved at the suggestion of ,admiral ,fitz,roy1 and now presents to the water a smooth cylindrical surface1 with rounded ends1 and without projection of fastenings4 ,in surveying expeditions1 this instrument would be found useful in giving notice of variation of depth of water1 and of the necessity for taking soundings4 ,a diminution of the temperature of water has been observed by scientific voyagers to accompany diminution of depth1 as on nearing land1 or approaching hidden rocks or shoals4 ,attention would also thus be attracted to the vicinity of icebergs4 ,this thermometer might easily be modified to serve for several other important purposes1 such as the determination of the temperature of intermittent hot springs1 and mud volcanoes4 ,illustration3 ,fig4 #ga4 ,the principle of this thermometer is not altogether new2 but the duplicate arrangement of the bars1 which effectually prevents the movement of the indices by any shaking1 and the application are certainly novel4 ,professor ,trail1 in the ,library of ,useful ,knowledge1 writes3--,in #ahjc1 ,mr4 ,james ,crighton1 of ,glasgow1 published a new 'metallic thermometer1' in which the unequal expansion of zinc and iron is the moving power4 ,a bar is formed by uniting a plate of zinc 7fig4 #ga71 c d1 #h inches long1 #a inch broad1 and #a_/d inch thick1 to a plate of iron1 a b1 of the same length4 ,the lower extremity of the compound bar is firmly attached to a mahogany board at e e2 a pin1 f1 fixed to its upper end1 plays in the forked opening in the short arm of the index1 g4 ,when the temperature is raised1 the superior expansion of the zinc1 c d1 will bend the whole bar1 as in the figure2 and the index1 g1 will move along the graduated arc1 from right to left1 in proportion to the temperature4 ,in order to convert it into a register thermometer1 ,crighton applied two slender hands1 h h1 on the axis of the index2 these lie below the index1 and are pushed in opposite directions by the stud1 i1--a contrivance seemingly borrowed from the instrument of ,fitzgerald1 a complicated metallic thermometer1 described by the ,professor previously4 ,,chapter ,x4 ,,boiling-,,point ,,thermometers4 #ia4 ,ebullition4--,the temperature at which a fluid boils is called the boiling-point of that particular fluid4 ,it is different for different liquids2 and1 moreover1 in the same liquid it varies with certain changes of circumstance4 ,thus the same liquid in various states of purity would have its boiling temperature altered in a slight degree4 ,there is also an intimate connection with the pressure under which a fluid is boiled1 and its temperature of ebullition4 ,liquids boiled in the open air are subjected to the atmospheric pressure1 which is well known to vary at different times and places2 and the boiling-point of the liquid exhibits corresponding changes4 ,when the pressure is increased on the surface of any fluid1 the temperature of ebullition rises2 and with a decrease of pressure1 the boiling goes on at a lower degree of heat4 ,in the case of water1 we commonly state the boiling-point to be #bab deg4 ,f42 but it is only so at the level of the sea1 under the mean pressure of the atmosphere1 represented1 in the latitude of ,london1 by a column of #bi4ije inches of mercury1 at a temperature of #cb deg4 ,f41 and when the water is fresh and does not contain any matter chemically dissolved in it4 ,when steam is generated and confined in a boiler1 the pressure upon the boiling water may be several times greater than that of the atmosphere4 ,experimentally it has been found1 that if the pressure in the boiler be #be lbs4 on the square inch1 the temperature of the boiling water1 and of the steam likewise1 is raised to #bda deg42 while under the exhausted receiver of an air-pump1 water will boil at #ahe deg41 when the pressure is reduced to #ag inches of mercury4 #ib4 ,relation between the ,boiling-,point and ,elevation4--,now1 as the atmospheric pressure is diminished by ascent1 as shown by the fall of mercury in the barometer1 it follows that in elevated localities water1 or any other fluid1 heated in the open air1 will boil at a temperature lower than at the sea-level4 ,therefore1 there must be some relation between the height of a hill1 or mountain1 and the temperature at which a fluid will boil at that height4 ,hence1 the thermometer1 as used to determine the boiling-point of fluids1 is also an indicator of the atmospheric pressure2 and may be used as a substitute for the barometer in measuring elevations4 ,if the atmospheric pressure were constant at the sea-level1 and always the same for definite heights1 we might expect the boiling-points of fluids also to be in exact accordance with height2 and the relation once ascertained1 we could readily1 by means of the thermometer and boiling water1 determine an unknown height1 or for a known elevation assert the boiling temperature of a liquid4 ,however1 as the atmospheric pressure is perpetually varying at the same place1 within certain limits1 so there are1 as it were1 sympathetic changes in the boiling temperatures of fluids4 ,it follows from this1 that heights can never be accurately measured1 either by the barometer or the boiling-point thermometer1 by simply observing at the places whose elevations are required4 ,to determine a height with any approach to accuracy1 it is necessary that a similar observation should be made at the same time at a lower station1 not very remote laterally from the upper1 and that they should be many times repeated4 ,when such observations have been very carefully conducted1 the height of the upper station above the lower may be ascertained with great precision1 as has been repeatedly verified by subsequent trigonometrical measurement of elevations so determined4 ,if the lower station be at the sea-level1 of course the absolute height of the upper is at once obtained4 #ic4 ,mountain ,thermometer2 sometimes called ,hypsometric ,apparatus4--,we have now to examine the construction of the boiling-point thermometer1 and its necessary appendages1 as adapted for the determination of heights4 ,messrs4 ,negretti and ,zambra's arrangement of the instrument is shown in figures #gb and #gc4 ,illustration3 ,fig4 #gb4 ,illustration3 ,fig4 #gc4 ,the thermometer is made with an elongated bulb1 so as to be as sensitive as possible4 ,the scale1 about a foot long1 is graduated on the stem1 and ranges from #ahj deg4 to #bad deg41 each degree being sufficiently large to show the divisions of tenths of a degree4 ,a sliding metallic vernier might perhaps with advantage be attached to the stem1 which would enable the observer to mark hundredths of a degree2 which1 however1 he can pretty well do by estimation4 ,the boiler is so contrived as to allow1 not only the bulb1 but the stem also of the thermometer1 to be surrounded by the steam4 ,the arrangement is readily understood by reference to the accompanying diagram1 fig4 #gc4 ,c1 is a copper boiler1 supported by a tripod stand so as to allow a spirit-lamp1 ,a1 made of metal to be placed underneath4 ,the flame from the lamp may be surrounded by a fine wire gauze1 ,b1 which will prevent it being extinguished when experimenting in the external air4 ,e ,e ,e1 is a three-drawn telescope tube1 proceeding from the boiler1 and open also at top4 ,another tube1 similarly constructed1 envelops this1 as shown by ,d ,d ,d4 ,this tube is screwed to the top of the boiler1 and has two openings1 one at the top to admit the thermometer1 the other low down1 ,g1 to give vent to the steam4 ,as the steam is generated1 it rises in the inner tube1 passes down between the tubes1 and flows away at ,g4 ,the thermometer is passed down1 supported by an india-rubber washer1 fitting steam tight1 so as to leave the top of the mercury1 when the boiling-point is attained1 sufficiently visible to make the observation4 ,the telescopic movement1 and the mode of supporting the thermometer1 enable the observer always to keep the bulb near the water1 and the double tube gives all the protection required to obtain a steady boiling-point4 ,some boiling-point thermometers are constructed with their scales altogether exposed to the air1 which may be very cold1 and consequently may contract to some extent the thread of mercury outside the boiler4 ,the steam1 having the same temperature as the boiling water1 keeps the tube1 throughout nearly its whole length1 at the same degree of heat1 in the apparatus described4 ,the whole can be packed in a tin case very compactly and securely for travelling1 as in fig4 #gb4 ,directions for ,using4--,when the apparatus is required for practical use1 sufficient water must be poured into the boiler to fill it about one third1 through an opening1 ,f1 which must be afterwards closed by the screw plug4 ,then apply the lighted lamp4 ,in a short time steam will issue from ,g2 and the mercury in the thermometer1 kept carefully immersed1 will rise rapidly until it attains a stationary point1 which is the boiling temperature4 ,the observation should now be taken and recorded with as much accuracy as possible1 and the temperature of the external air must be noted at the same time by an ordinary thermometer4 ,the water employed should be pure4 ,distilled water would therefore be the best4 ,if a substance is held mechanically suspended in water1 it will not affect the boiling-point4 ,thus1 muddy water would serve equally as well as distilled water4 ,however1 as it cannot be readily ascertained that nothing is dissolved chemically when water is dirty1 we are only correct when we employ pure water4 #id4 ,precautions to ensure correct ,graduation4--,those who possess a boiling-point thermometer should satisfy themselves that it has been correctly graduated4 ,to do this1 it is advisable to verify it with the reading of a standard barometer reduced to #cb deg4 ,f4 ,the table of ,vapour ,tension 7given at p4 #fb7 will furnish the means of comparison4 ,thus1 if the reduced reading of the barometer1 corrected also for latitude1 be #bi4ibb1 the thermometer should show #bab deg4 as the boiling-point of water at the same time and place2 if #bi4gde1 the thermometer should read #baa4g2 and so on as per table4 ,in this way the error of the chief point of the scale can be obtained4 ,other parts of the scale may be checked with a standard thermometer1 by subjecting both to the same temperature1 and comparing their indications4 ,the graduations as fixed by some makers are not always to be trusted2 and this essential test should be conducted with the utmost nicety and care4 ,admiral ,fitz,roy writes1 in his ,notes on ,meteorology3--,each degree of the boiling-point thermometer is equivalent to about #eej feet of ascent1 or one-tenth to #ee feet2 therefore1 the smallest error in the graduation of the thermometer itself will affect the height deduced materially4 ,in the thermometer which is graduated from #bab deg4 7the boiling-point7 to #ahj deg41 similarly to those intended for the purpose of measuring heights1 there must have been a starting point1 or zero1 from which to begin the graduation4 ,i have asked an optician in ,london how he fixed that zero1 the boiling-point4 ',by boiling water at my house1' he replied4 ',where is your house8' ,in such a part of the town1 he answered4 ,i said3 ',what height is it above the sea8' to which he replied1 ',i do not know2' and when ,i asked the state of the barometer when he boiled the water1 whether the mercury was high or low1 he said that he had not looked at it6 ,now1 as this instrument is intended to measure heights and to decide differences of some hundred1 if not thousand feet upwards1 at least one should endeavour to ascertain a reliable starting point4 ,from inquiries made1 ,i believe that the determination of the boiling-point of ordinary thermometers has been very vague1 not only from the extreme difficulties of the process itself 7which are well known to opticians71 but from the radical errors of not allowing for the pressure of the atmosphere at the time of graduation--which may be much1 even an inch higher or lower1 than the mean1 or any given height--while the elevation of the place above the level of the sea is also unnoticed4 ,then there is another source of error1 a minor one1 perhaps3 the inner limit1 the #ahj deg4 point1 is fixed only by comparison with another thermometer2 it may be right1 or it may be very much out1 as may be the intermediate divisions2 for the difficulty of ascertaining degree by degree is great3 and it must be remembered that the measurement of a very high mountain depends upon those inner degrees from #bjj deg4 down to #ahj deg41 thereabouts4 ,hence1 the difficulty of making a reliable observation by boiling water seems to be greater than has been generally admitted4 #ie4 ,method of ,calculating ,heights from ,observations with the ,mountain ,thermometer4--,having considered how to make observations with the proper care and accuracy1 it becomes necessary to know how to deduce the height by calculation4 ,that a constant intimate relation exists between the boiling temperature of water and the pressure of the air1 we have already learned4 ,this knowledge is the result of elaborate experiments made by several scientific experimentalists1 who have likewise constructed formulae and tables for the conversion of the boiling temperatures into the corresponding pressures of vapour1 or1 which is equivalent1 of the atmosphere1 when the operation is performed in the open air4 ,as might be expected1 there is not a perfect accord in the results arrived at by different persons4 ,regnault is the most recent1 and his experiments are considered the most reliable4 ,from ,regnault's table of vapour tension1 we can obtain the pressure in inches of mercury at #cb deg41 which corresponds to the observed boiling-point2 or vice versa1 if required4 ,from the pressure1 the height may be deduced by the method for finding heights by means of the barometer4 ,the following table expresses very nearly the elevation in feet corresponding to a fall of #a deg4 in the temperature of boiling water3-- ,boiling ,temperatures ,elevation in ,feet between4 for each ,degree4 #bad deg4 and #baj-- #ebj #baj and #bjj-- #ecj #bjj and #aij #eej #aij and #ahj #egj ,these numbers agree very well with the results of theory and actual observation4 ,the assumption is that the boiling-point will be diminished #a deg4 for each #ebj feet of ascent until the temperature becomes #baj deg41 then #ecj feet of elevation will lower it one degree until the water boils at #bjj deg41 and so on2 the air being at #cb deg4 ,let ,h represent the vertical height in feet between two stations2 ,b and b1 the boiling-points of water at the lower and upper stations respectively2 f1 the factor found in the above table4 ,then ,h f7,b - b7 ,further1 let m be the mean temperature of the stratum of air between the stations4 ,now1 if the mean temperature is less than #cb deg41 the column of air will be shorter2 and if greater1 longer than at #cb deg4 ,according to ,regnault1 air expands #a_/dia4ac or 4#jjbjcf of its volume at #cb deg41 for each degree increase of heat4 ,calling the correction due to the mean temperature of air ,c1 its value will be found from the equation1 ,c ,h 7m - #cb7 4#jjbjcf ,calling the corrected height ,h'1 it will be found from the formula1 ,h' ,h ,h 7m - #cb7 4#jjbjcf that is1 ,h' ,h #a 7m - #cb7 4#jjbjcf and substituting the value of ,h1 ,h' f7,b - b7 #a 7m - #cb7 4#jjbjcf ,strictly1 according to theoretical considerations1 there is a correction due to latitude1 as in the determination of heights by the barometer2 but its value is so small that it is practically of no importance4 ,if a barometer be observed at one of the stations1 the table of vapour tensions 7p4 #fb7 will be useful in converting the pressure into the corresponding boiling-point1 or vice versa2 so that the difference of height may be found either by the methods employed for the boiling-point thermometer or the barometer4 ,in conclusion1 it may be remarked that observers who have good instruments at considerable elevations1 as sites on mountains or plateaus1 would confer a benefit to science1 by registering for a length of time the barometer along with the boiling temperature of water1 as accurately as possible4 ,such observations would serve to verify the accuracy of theoretical deductions1 and fix with certainty the theoretical scale with the barometer indications4 ,example1 in calculating ,heights from the ,observations of the ,boiling-point of ,water4--#a4 ,at ,geneva the observed boiling-point of water was #bji deg4#cce2 on the ,great ,st4 ,bernard it was #aig deg4#fd2 the mean temperature of the intermediate air was #fc deg4#e2 required the height of the ,great ,st4 ,bernard above ,geneva4 ,method by formula3-- ,h' f 7,b - b7 #a 7m - #cb deg47 4#jjbjcf ,in this case f is between #ecj and #eej1 or #edj4 ,b #bji4cce m #fc4e b #aig4fd #cb ------- ----- #aa4fie #ca4e f #edj 4#jjbjcf ------- --------- #fcae4c #j4jfdacdj #a4jfd #a ------- ----- ,h' #fgai4e feet4 #a4jfd ,method by ,tables supplied with boiling-point apparatus made by ,messrs4 ,negretti and ,zambra3-- #bji4cce gives #adfd in ,table ,i4 #aig4fd #ggcf ---- #fbgb #fc4e #a4jg in ,table ,,ii4 ---- ,height #fgaa #if4 ,thermometers for ,engineers4--#ast4 ,salinometer4--,under the circumstances at which fresh water boils at #bab deg41 sea water boils at #bac deg4#b4 ,the boiling temperature is raised by the chemical solution of any substance in the water1 and the more with the increase of matter dissolved4 ,from a knowledge of this principle1 marine engineers make use of the thermometer to determine the amount of salts held in solution by the water in the boilers of sea-going steamers4 ,common sea-water contains #a_/cc of its volume of salt and other earthy matters4 ,as evaporation proceeds1 the solution becomes proportionally stronger1 and more heat is required to produce steam4 ,the following table from the work of ,messrs4 ,main and ,brown1 on the ,marine ,steam-,engine1 shows the relation between the boiling-point under the mean pressure of the atmosphere1 or #hj inches of mercury1 and the proportion of matter dissolved in the water3-- ,proportion of ,salt in #ajj parts of water #j ,boiling-point #bab deg4 #a_/cc #bac4b #b_/cc #bad4d #c_/cc #bae4e #d_/cc #baf4f #e_/cc #bag4i #f_/cc #bai4j #g_/cc #bbj4b #h_/cc #bba4d #i_/cc #bbb4e #aj_/cc #bbc4g #aa_/cc #bbd4i #ab_/cc #bbf4j ,when the salts in solution amount to #ab_/cc1 the water is saturated4 ,it has also been ascertained that1 when a solution of #d_/cc is attained1 incrustation of the substances commences on the boiler4 ,hence1 it is a rule with engineers to expel some of the boiling water1 when the thermometer indicates a temperature of #baf deg41 and introduce some more cold water1 in order to prevent incrustation1 which not only injures the boiler1 but opposes the passage of heat to the water4 ,the thermometer used for this purpose should be very accurately graduated1 and the scale must be considerably higher than1 though it need not read much below #bab deg4 #bnd4 ,pressure ,gauge4--,the elasticity of gases augments by increase of temperature1 and vice versa2 it follows1 therefore1 that when steam is generated in a closed boiler1 its temperature rises beyond the boiling temperature of #bab deg41 owing to the increased pressure upon the water4 ,the law connecting the pressure and the corresponding temperature of steam is the same as that upon which the boiling of fluids under diminished atmospheric pressure takes place4 ,hence1 the indications of the thermometer become exponents of steam pressure4 ,engineers are furnished1 in works on the steam-engine1 with tables1 from which the pressure corresponding to a given temperature1 or the converse1 can be obtained by mere inspection4 ,illustration3 ,fig4 #gd4 ,fig4 #gd represents the thermometer employed as a steam-pressure gauge4 ,it is fitted in a brass case1 with screw-plug and washers for closing the boiler when the thermometer is not in use4 ,the scale shows the pressure corresponding to the temperature1 from #ae to #abj lbs41 above the atmospheric pressure1 which is usually taken as #ae lbs4 on the square inch4 ,,chapter ,,xi4 ,,instruments ,,for ,,ascertaining ,,the ,,humidity ,,of ,,the ,,air4 #ig4 ,hygrometric ,substances4--,the instruments devised for the purpose of ascertaining the humidity of the atmosphere are termed hygrometers4 ,the earliest invented hygrometers were constructed of substances readily acted upon by the vapour in the air1 such as hair1 grass1 seaweed1 catgut1 c41 which all absorb moisture1 and thereby increase in length1 and when deprived of it by drying they contract4 ,toy-like hygrometers1 upon the principle of absorption1 are still common as ornaments for mantel-pieces4 ,a useful little instrument of this class1 formed from the beard of the wild oat1 is made to resemble a watch in external appearance1 and is designed to prove the dampness or dryness of beds3 a moveable hand points out on the dial the hygrometric condition of the clothes upon which the instrument is laid4 #ih4 ,saussure's ,hygrometer1 formerly used as a meteorologic instrument1 but now regarded as an ornamental curiosity1 is represented in fig4 #ge4 ,its action depends upon a prepared hair1 fixed at one end to the frame of the instrument1 and wound round a pulley at the other4 ,the pulley carries a pointer which has a counterpoise sufficient to keep the hair stretched4 ,by this means the shrinking and lengthening of the hair cause the pointer to traverse a graduated arc indicating the relative humidity4 ,illustration3 ,fig4 #ge4 ,such instruments1 however ingenious1 are not of scientific value2 because they do not admit of rigid comparison1 are liable to alter in their contractile and expansive properties1 and cannot be made to indicate precisely alike4 #ii4 ,dew-,point4--,the amount of water which the air can sustain in an invisible form increases with the temperature2 but for every definite temperature there is a limit to the amount of vapour which can be thus diffused4 ,when the air is cooled1 the vapour present may be more than it can sustain2 part will then be condensed as dew1 rain1 hail or snow1 according to the meteorologic circumstances4 ,the temperature which the air has when it is so fully saturated with vapour that any excess will be deposited as dew1 is called the dew-point4 #ajj4 ,drosometer4--,to measure the quantity of dew deposited each night1 an instrument is used called a ,drosometer4 ,the most simple process consists in exposing to the open air bodies whose exact weight is known1 and then weighing them afresh after they are covered with dew4 ,according to ,wells1 locks of wool1 weighing about eight grains1 are to be preferred1 which are to be divided formed into spherical masses of the diameter of about two inches4--,koemtz4 #aja4 ,humidity4--,the proportion existing between the amount of vapour actually present in the air at any time1 and the quantity necessary to completely saturate it1 is called the degree of humidity4 ,it is usually expressed in a centesimal scale1 #j being perfect dryness1 and #ajj complete saturation4 ,the pressure1 or tension1 of vapour at the dew-point temperature1 divided by the tension of vapour at the air temperature and the quotient multiplied by #ajj1 gives the degree of humidity4 7,regnault's ,tables should be used47 ,hence the utility of instruments for determining the dew-point4 #ajb4 ,leslie's ,hygrometer4--,this instrument consists of a glass syphon tube1 terminated with a bulb or ball at each end1 turned outwards from each other1 as in fig4 #gf4 ,the tube is partly filled with concentrated sulphuric acid1 tinged by carmine4 ,one of the balls is covered smoothly with fine muslin1 and is kept continually moistened with pure water1 drawn from a vase placed near it by the capillary attraction of a few strands of clean cotton-wick4 ,the descent of the coloured liquid in the other stem will mark the diminution of temperature caused by the evaporation of the water from the humid surface4 ,the drier the ambient air is1 the more rapidly will the evaporation go on2 and the cold produced will be greater4 ,when the air is nearly saturated with moisture1 the evaporation goes on slowly2 the cold produced is moderate1 because the ball regains a large portion of its lost heat from surrounding bodies2 and the degree of refrigeration of the ball is an index of the dryness of the air4 ,illustration3 ,fig4 #gf4 ,should the water become frozen on the ball1 this hygrometer will still act2 for evaporation goes on from the surface of ice in proportion to the dryness of the air4 ,leslie estimates1 that when the ball is moist1 air1 at the temperature of the ball1 will take up moisture equal to the sixteen-thousandth part of its weight1 for each degree of his hygrometer2 and as ice in melting requires one-seventh of the caloric consumed in converting water into vapour1 when the ball is frozen1 the hygrometer will sink more than when wet by #a deg4 in #g deg42 and hence1 in the frozen state1 we must increase the value of the degrees one-seventh3 so that each of them will correspond to an absorption of moisture equal to one-fourteen-thousandth part of the weight of the air4 ,when this hygrometer stands at #ae deg41 the air feels damp2 from #cj deg4 to #dj deg41 we reckon it dry2 from #ej deg4 to #fj deg41 very dry2 and from #gj deg4 upwards1 we should call it intensely dry4 ,a room would feel uncomfortable1 and would probably be unwholesome1 if the instrument in it did not reach #cj deg4#h ,in thick fogs it keeps almost at the beginning of the scale4 ,in winter1 in our climate1 it ranges from #e deg4 to #ae deg42 in summer often from #ae deg4 to #ee deg42 and sometimes attains #hj deg4 or #ij deg4 ,the greatest degree of dryness ever noticed by ,leslie was at ,paris1 in the month of ,september1 when the hygrometer indicated #abj deg4--,professor ,trail1 in ,library of ,useful ,knowledge4 ,in estimating the value of the indications of this hygrometer1 it should be borne in mind that the scale adopted by ,leslie was millesimal1 that is to say1 from the freezing to the boiling-point of water was divided into a thousand parts2 ten millesimal degrees are therefore equal to one of the scale of ,celsius4 #ajc4 ,,daniel',s ,,hygrometer4 ,this instrument was invented about the year #ahbj1 by ,professor ,daniel1 the distinguished author of ,meteorological ,essays2 and it entirely superseded all hygrometers depending upon the absorption of moisture4 ,the form of the instrument is shown in fig4 #gg4 ,illustration3 ,fig4 #gg4 ,it consists of a glass tube1 about one-eighth of an inch in diameter of bore1 bent twice at right angles1 and terminated1 at each end1 in a bulb about one inch and a quarter in diameter4 ,in one limb of the tube is enclosed a delicate thermometer1 which descends to the centre of the adjoining bulb1 which is about three-parts filled with sulphuric ether4 ,all the other parts of the tube are carefully freed from air1 so that they are occupied by the vapour of the ether4 ,this bulb is generally made of black glass2 the other is transparent1 but covered with a piece of fine muslin4 ,the support for the tube has a thermometer attached1 which shows the temperature of the external air4 ,the tube can be removed from the stand1 and the parts are made to pack1 with a necessary phial of ether1 in a small box1 which can easily be got into the pocket4 ,how to use the ,hygrometer4--,this instrument gives the dew-point by direct observation1 which must be made in the following manner3--,having fixed the tube upon the stand1 with the bulbs vertically downward1 the ether is all caused to flow into the lower ball by inclining the tube4 ,the temperature of the air is noted by the exposed thermometer4 ,then some ether is poured1 from a dropping tube fitting into the neck of the phial1 upon the muslin-covered bulb4 ,the rapid evaporation of this ether cools the bulb and causes condensation of the ethereal vapour in its interior4 ,this gives rise to rapid evaporation of the ether in the lower bulb1 whereby its temperature is greatly reduced4 ,the air in the vicinity is deprived of its warmth by the cold bulb1 and is soon cooled to the temperature at which it is perfectly saturated with the vapour which it contains4 ,cooled ever so little below this temperature1 some aqueous vapour will be condensed1 and will form a dew upon the black-glass bulb4 ,at the first indication of the deposit of dew the reading of the internal thermometer is taken3 which is the dew-point4 ,this hygrometer has undeniable disadvantages4 ,the surface upon which the dew condenses is small1 and requires a peculiar direction of light in which to see it well4 ,the observer1 having his attention on the bulb and the thermometer1 cannot always fix with precision the dew-point2 and hence he is recommended to note the temperature at the appearance and at the disappearance of the dew1 in order that the chance of error may be diminished4 ,without doubt1 the necessarily long continuance of the observer near the instrument influences1 to some extent1 the observed temperatures2 and the difficulty of not being always able to procure pure ether for the experiments is not the least of the drawbacks to the use of the instrument4 ,some of these disadvantages are obviated in ,regnault's hygrometer4 #ajd4 ,,regnault',s ,,condenser ,,hygrometer 7,fig4 #gh7 consists of a tube1 ,c1 made of silver1 very thin1 and perfectly polished2 the tube is larger at one end than the other1 the large part being #a4h inches in depth1 by #j4h in diameter2 this is fitted tightly to a brass stand1 ,b1 with a telescopic arrangement for adjusting when making an observation4 ,illustration3 ,fig4 #gh4 ,the tube1 ,c1 has a small lateral tubulure1 to which is attached an ,india-rubber tube1 with ivory mouth-piece2 this tubulure enters ,c at right angles near the top1 and traverses it to the bottom of the largest part4 ,a delicate thermometer1 ,d1 is inserted through a cork1 or ,india-rubber washer1 at the open end of the tube1 ,c1 the bulb of which descends to the centre of its largest part4 ,g is an attached thermometer for taking the temperature of the air1 and ,f is a bottle containing ether4 ,to use the ,condenser ,hygrometer1 a sufficient quantity of ether is poured into the silver tube to cover the thermometer bulb3 on allowing air to pass bubble by bubble through the ether1 by breathing in the tube1 ,e1 an uniform temperature will be obtained2 if the ether continues to be agitated1 by breathing briskly through the tube a rapid reduction of temperature will be the result2 at the moment the ether is cooled down to the dew-point temperature1 the external surface of that portion of the silver tube containing ether will become covered with a coating of moisture1 and the degree shown by the thermometer at that instant will be the temperature of the dew-point4 ,this form of hygrometer1 for ascertaining by direct observation the dew-point1 is so superior to ,daniell's1 both from its being more certain in its indications and economical in use1 that ,messrs4 ,negretti and ,zambra have been induced to modify it1 and reduce its price to little more than that of a good ,daniell's ,hygrometer4 #aje4 ,temperature of ,evaporation4--,when the air is not saturated with vapour1 evaporation is going on with more or less activity1 according as the temperature is high or low1 rising or falling4 ,now vapour cannot be formed without an expenditure of heat2 as we invariably find that the process of evaporation lowers the temperature of the liquid from which the vapour is produced1 and1 by communication1 that of contiguous substances also4 ,thus the emigrant1 crossing the line under the scorching influence of the vertical sun1 wraps a wet towel round his can of water1 swings it in the breeze1 to evaporate the moisture of the towel1 and obtains a glass of cool water4 ,so also1 ,european residents in ,india1 during the hot season1 spread out mats in their apartments1 and keep them wet1 in order that the evaporation may cool the air4 ,this principle has been applied1 for the purpose of ascertaining the hygrometric condition of the air1 in the instrument known as ,mason's hygrometer1 or psychrometer1 which is now in general use1 from its simplicity1 accuracy1 and ease of observing4 #ajf4 ,,mason',s ,,hygrometer4 ,the ,dry and ,wet ,bulb ,hygrometer1 or ,psychrometer1 known also as ,mason's hygrometer 7fig4 #gi71 consists of two parallel thermometers1 as nearly identical as possible1 mounted on a wooden bracket1 one marked dry1 the other wet4 ,the bulb of the wet thermometer is covered with thin muslin1 and round the neck is twisted a conducting thread of lamp-wick1 which passes into a vessel of water1 placed at such a distance as to allow a length of conducting thread1 of about three inches2 the cup or glass is placed on one side1 and a little beneath1 so that the water within may not affect the reading of the dry bulb thermometer4 ,in observing1 the eye should be placed on a level with the top of the mercury in the tube1 and the observer should refrain from breathing whilst taking an observation4 ,illustration3 ,fig4 #gi4 ,the dry bulb thermometer indicates the temperature of the air itself2 while the wet bulb1 cooled by evaporation1 shows a lower temperature according to the rapidity of evaporation4 ,to find the ,dew-point4--,from the readings of the two thermometers1 the dew-point can be deduced by formulae 7that known as ,apjohn's is considered the most theoretically true71 or from the valuable ,hygrometric ,tables by ,j4 ,glaisher1 ,esq41 ,f4,r4,s4 ,for practical purposes in estimating the comparative humidity1 the annexed table1 which is a reduction from ,mr4 ,glaisher's elaborate work1 will be sufficient2 it will at least serve to assist in familiarising the inexperienced in the value of the psychrometer's indications3-- ---------------------------------------- -- ,difference between ,dry-bulb and ,wet-bulb ,readings4 ,temperature ----------------------------- by the #b deg4 #d deg4 #f deg4 #h deg4 #aj deg4 #ab deg4 ,dry ,bulb ----------------------------- ,thermometer4 ,degree of ,humidity4 ---------------------------------------- -- #cd deg4 #gi #fc #ej 44 44 44 #cf #hb #ff #ec 44 44 44 #ch #hc #fh #ef #de 44 44 #dj #hd #gj #eh #dg 44 44 #db #hd #ga #ei #di 44 44 #dd #he #gb #fj #ej 44 44 #df #hf #gc #fa #ea 44 44 #dh #hf #gc #fb #eb #dd 44 #ej #hf #gd #fc #ec #de 44 #eb #hf #gd #fd #ed #df 44 #ed #hf #gd #fd #ee #dg 44 #ef #hg #ge #fe #ef #dh 44 #eh #hg #gf #ff #eg #di 44 #fj #hh #gf #ff #eh #ej #dc #fb #hh #gg #fg #eh #ej #dd #fd #hh #gg #fg #ei #ea #de #ff #hh #gh #fh #fj #eb #de #fh #hh #gh #fh #fj #eb #df #gj #hh #gh #fi #fa #ec #dg #gb #hi #gi #fi #fa #ed #dh #gd #hi #gi #gj #fb #ee #dh #gf #hi #gi #ga #fc #ee #di #gh #hi #gi #ga #fc #ef #ej #hj #ij #hj #ga #fc #ef #ej #hb #ij #hj #gb #fd #eg #ea #hd #ij #hj #gb #fd #eg #ea #hf #ij #hj #gb #fd #eh #eb ---------------------------------------- -- ,the total quantity of aqueous vapour which at any temperature can be diffused in the air being represented by #ajj1 the per-centage of vapour actually present will be found in the table opposite the temperature of the dry thermometer1 and under the difference between the dry-bulb and wet-bulb temperatures4 ,the degree of humidity for intermediate temperatures and differences to those given in the table can be easily estimated sufficiently accurately for most practical purposes4 ,the difference between the two thermometer readings taken from the reading of the wet bulb1 gives the dew-point very nearly1 when the air is at any temperature between freezing and #hj deg4 ,this simple rule will be found serviceable to horticulturists1 since it will enable them to estimate the chilling effect of dew or hoar-frost on tender plants4 ,use as an ,indicator of ,weather4--,in our climate1 the usual difference between the thermometer readings1--in the open air1 shaded from the sun1 reflected heat1 and currents of air1--ranges from one to twelve degrees4 ,in hot and dry climates1 as ,india and ,australia1 the range out of doors has been found as much as #cj deg41 occasionally4 ,when the moisture is frozen1 the bulb should be wetted afresh1 and the reading taken just before it again freezes2 but the observation then is of little value1 and for general purposes need not be taken1 as the air is known to be dry in frosty weather4 ,the muslin or cotton rag should be washed once or twice a week by pouring water over the bulb2 and it should be replaced by a fresh piece at least once a month4 ,accuracy depends very much upon keeping the wet bulb clean1 and not too wet4 ,in connection with the barometer1 this hygrometer is very useful1 not only on land1 but especially at sea1 where other kinds of hygrometers cannot be practically used4 ,a fall in the barometer is indicative of coming wind or rain3 if the hygrometer shows increasing dampness by the difference of the readings becoming smaller1--rain may therefore be anticipated4 ,on the contrary1 if the hygrometer shows continuing or increasing dryness1 a stronger wind is probable1 without rain4 ,domestic ,uses4--,mason's hygrometer is useful in regulating the moisture of the air of apartments2 a difference in the thermometer readings of from #e deg4 to #h deg4 being considered healthy4 ,many complaints require that the temperature and humidity of the air which the invalid breathes should be carefully regulated4 ,hence it is a valuable household instrument4 ,in a room1 it should be placed away from the fire as much as possible1 but not exposed to draughts of air4 ,figs4 #hj and #ha show cheap arrangements of the instrument for domestic purposes4 ,other arrangements are given to the instrument to make it suitable for exhibiting the hygrometrical state of the air in hot-houses1 conservatories1 malting-houses1 warehouses1 manufactories1 c4 ,illustration3 ,fig4 #hj4 ,illustration3 ,fig4 #ha4 ,illustration3 ,fig4 #hb4 ,fig4 #hb shows the instrument arranged on brass tripod stand1 with folding legs and metal cover1 to render it portable4 #ajg4 ,self-,registering ,hygrometer4--,a maximum thermometer and a minimum thermometer1 each fitted up as a wet-bulb thermometer1 record the highest and lowest temperature of evaporation during the interval of observation4 ,negretti's mercurial maximum1 and an alcohol minimum1 answer best4 #ajh4 ,causes of ,dew4--,the aqueous vapour of our atmosphere is a powerful radiant2 but it is diffused through air which usually exceeds its own mass more than one hundred times4 ,not only1 then1 its own heat1 but the heat of the large quantity of air which surrounds it1 must be discharged by the vapour1 before it can sink to its point of condensation4 ,the retardation of chilling due to this cause enables good solid radiators1 at the earth's surface1 to outstrip the vapour in their speed of refrigeration2 and hence1 upon these bodies1 aqueous vapour may be condensed to liquid1 or even congealed to hoar-frost1 while at a few feet above the surface it still maintains its gaseous state4#i ,the amount of moisture so deposited will vary with different atmospheric conditions4 ,if the sky be decidedly cloudy or misty1 the heat radiated from the earth will be partly restored by counter-radiation from the visible vapour2 the cooling of the earth's surface will1 therefore1 take place slowly1 and little dew will be deposited4 ,on the other hand1 if the air contain transparent vapour1 and the sky appear clear1 the counter-radiation will be less1 the earth will cool rapidly1 and the deposit of dew will be copious2 provided the night be comparatively calm1 for1 when the wind blows1 the circulating air supplies heat to the radiating substances1 and prevents any considerable chilling4 ,the dew which falls in tropical countries greatly exceeds in abundance what we experience in our climate2 because the air is there1 from the great heat1 capable of sustaining a large amount of vapour in the transparent state1 and the conditions most favourable for a maximum reduction of temperature by radiation are present4 ,at those places1 or upon those substances which cool the lowest and most readily1 the dew falls most copiously4 ,illustration3 ,fig4 #hc4 #aji4 ,plan of ,exposing ,thermometers1 c4--,figure #hc is an illustration of a convenient slab for supporting thermometers in an exposed position attached to a stand 7such as ,glaisher's1 described in ,chapter ,,xvi47 for ordinary scientific observations4 ,it has a projecting ledge1 ,b1 to carry off rain from the instruments1 the slab1 ,a1 being erected vertically4 ,the hygrometer is placed at ,e1 with the vase of water at ,f4 ,an alcohol minimum thermometer is represented at ,c1 in the position most favourable to its certain action2 and at ,d is shown one of ,negretti ,zambra's maximum thermometers1 the position of which may be more nearly horizontal than there exhibited1 although a slight depression of the bulb-end of the frame is desirable1 but not necessary1 as this thermometer can be used in any position4 ,,chapter ,,xii4 ,,instruments ,,used ,,for ,,measuring ,,the ,,rainfall4 ,the instruments in use for measuring the quantity of rain which falls on a given spot are of very simple construction4 ,perhaps the simplest is3-- #aaj4 ,howard's ,rain-,gauge4--,it consists of a copper funnel1 a stout glass or stone bottle1 and a measuring glass4 ,the bottle is to be placed upon the ground1 with the funnel resting on its neck4 ,a brass band or cylinder fixed upon the outer surface of the funnel envelops the neck of the bottle1 and the pipe of the funnel extends nearly to the bottom of the bottle2 so that loss by evaporation is avoided as much as possible4 ,the receiving space of the funnel is formed by a brass ring1 five inches in diameter1 very accurately turned4 ,the measuring vessel enables the observer to note the rainfall in inches1 tenths1 and hundredths of an inch4 ,illustration3 ,fig4 #hd4 #aaa4 ,glaisher's ,rain-,gauge4--,the rain-gauge designed by ,mr4 ,glaisher1 the well-known meteorologist1 and used by most observers of the present day1 is arranged for the reception of the water which falls upon its receiving surface only1 and for the prevention of loss by evaporation4 ,the rain is first collected in a funnel1 ,b1 7fig4 #hd17 the receiving surface of which is turned in a lathe4 ,the conical surface of the funnel slopes to the pipe1 ,e1 at an angle of #fj deg4 from the horizontal receiving surface4 ,the tube1 ,e1 is of small aperture1 and is bent up1 in order to retain the last few drops of rain1 so that the only opening for the escape of vapour may be closed as long as possible4 ,the funnel1 ,b1 fits upon the cylinder1 ,a1 tightly in the groove1 ,d4 ,a copper can is placed inside the cylinder1 ,a1 to receive the rain from the funnel4 ,once or twice a day1 or after a shower1 this can should be taken out1 and the water measured in the glass measure1 ,c1 which is graduated to hundredths of an inch1 according to the calculated quantity of water1 determined by the area of the receiving space4 ,in use1 this gauge should be partly sunk in the ground1 so that the top may be about five inches above it4 ,thus situated1 there will be little or no evaporation from it during any month of the year2 and the readings need not be taken daily1 although desirable4 #aab4 ,rain-,gauge with ,float4--,in this construction the graduated glass measure is dispensed with4 ,the cylinder of the gauge is made less in diameter than the funnel1 and a hollow1 very flattened spheroid of copper forming a float1 and carrying a vertical graduated boxwood scale which moves through the orifice of the funnel1 is placed in it4 ,as the rain accumulates the float rises1 and the amount of rain in the gauge is read upon the scale from the top of the gauge1 a bar1 having a hole at the centre for the passage of the scale1 being fixed diametrically across the receiving space of the funnel4 ,the gauge is provided at the bottom with a brass cock1 by which the water may be allowed to flow out of it whenever necessary4 ,this form of gauge is not very suitable for the measurement of small quantities2 but is admirably adapted for localities where the rainfall is excessive4 ,illustration3 ,fig4 #he4 #aac4 ,rain-,gauge with ,side-,tube4--,this instrument1 as represented in fig4 #he1 is a cylindrical vessel1 mounted on a base shaped as a frustum of a cone4 ,this base may be filled with sand or gravel to make the instrument stable1 so that when placed upon a lawn or in a garden it may have an ornamental appearance4 ,the funnel for collecting the rain is larger in diameter than the cylinder4 ,parallel to the cylinder1 and communicating with the lowest part of the interior and extending to its top1 is a graduated glass tube1 open at both ends4 ,the rain collected will rise as high in this tube as in the cylinder1 and its amount can therefore be read off without any trouble4 ,the gauge is emptied by the brass tap at the bottom of the cylinder4 #aad4 ,admiral ,fitz,roy's ,rain-,gauge4--,a form of rain-gauge1 very well adapted for expeditious observation at any time1 has been designed by ,admiral ,fitz,roy1 and extensively employed by his observers4 ,it is cylindrical in shape1 with the funnel let into the top2 and the rainfall is collected in an inner and much smaller cylinder1 so that a small fall is represented by a considerable depth of water in the gauge4 ,the amount of rain which has fallen is ascertained by a dipping tube1 similar in principle to the dipping syphon used by gaugers for taking out specimens of wines or spirits from casks by simply removing the bung4 ,a short1 vertical1 tubular opening provided with a cap1 which is attached to the instrument by a chain that it may not be lost1 is formed in the funnel4 ,the measuring tube1 which has a small hole at each end1 should be placed upright in the gauge2 then the thumb should be pressed over the upper aperture1 while the tube is lifted gently out1 holding in the lower part a quantity of water representing the depth of the rain in the gauge1 the upper edge of which is at the mark to be read off4 ,the glass tube is graduated to inches and tenths2 hundredths of an inch can be readily estimated by the eye4 ,the marks are fixed by actual trial with a standard gauge1 and are artificial1 not true1 inches4 #aae4 ,self-,registering ,rain-,gauge4--,the rain-gauge can be combined with clock-work and other mechanism so as to be self-recording of the amount of rain1 the time1 and duration of its fall4 ,for the details of construction the reader is referred to the next chapter1 where he will find the instrument described in connection with ,osler's anemometer1 as the pluviometer4 ,to observe and duly record the times of commencement and termination of rain is very desirable4 ,scarcely any observer can attempt to do this even approximately from personal observation4 ,hence the want of a cheap and simple self-recording rain-gauge is much felt1 the present construction being too expensive for all but a few individuals4 ,in #ahfb1 ,mr4 ,r4 ,strachan estimated the duration and amount of rain in ,london 7,gray's ,inn ,road7 as follows3-- ---------------------------------------- --------------------------- ,,months4 ,,inches4,,days4,,hours4 ,,months4 ,,inches4,,days4,,hours4 ---------------------------------------- ------------------- ,january4 #a4hf #ai #hh ,july4 #b4bg #ag #fh ,february4 #j4cg #i #be ,august4 #b4de #ab #gb ,march4 #c4dj #bb #acj ,september4 #a4gj #ab #ee ,april4 #b4cd #ad #hj ,october4 #c4bc #ba #id ,may4 #c4jd #af #ij ,november4 #a4ab #aj #ec ,june4 #b4de #bj #hc ,december4 #a4dd #ag #ff ---------------------------------------- --------------------------- ,during the year #ahfb1 the rainfall amounted to #be4fg inches4 ,rain fell on #agi days1 that is1 on nearly every other day4 ,the hours of rain were estimated at #ijd2 therefore1 if the rain had fallen continuously1 it would have lasted nearly #ch days and nights4#aj ,the value of similar estimates of the rainfall by numerous observers would be very great to meteorology4 #aaf4 ,the principle of measurement in all these gauges is the relation existing between the areas of the collecting and receiving surfaces2 that is1 between the area of the funnel into which the rain falls1 and the area of the cylinder which receives it4 ,in ,howard's and ,glaisher's gauges1 this cylinder is virtually the measuring glass itself2 in the others1 above described1 the measuring scales show the same depth of water as in the cylinder of the gauge4 ,the cylinder being of less diameter than the funnel1 and receiving all the rain collected by the funnel1 it follows that its contents will have an increased depth4 ,now equal cylindrical volumes1 having different diameters1 are to each other in length inversely as the squares of the diameters4 ,hence1 if the funnel be #i inches and the cylinder #c inches in diameter1 a fall of #a inch of rain will be represented in the gauge by #i inches2 for #c squared 3 #i squared 33 #a 3 x #i4 ,in this case1 therefore1 a length of nine inches of the measuring glass1 tube1 or scale1 would represent an inch of rainfall1 and be divided into tenths and hundredths of the artificial inch4 #aag4 ,position for ,rain-,gauge1 c4--,rain gauges should be placed on the ground1 in any position exposed to a free fall of rain1 snow1 or hail1 where neither walls1 buildings1 nor trees shelter or cause eddies of wind4 ,they should be supported by a frame1 or other means1 to prevent them being blown down by the wind1 but so that they can be readily emptied4 ,during snow or frost1 the gauge must be watched1 and its contents melted by placing it in a warm room1 either when the amount is to be measured1 or the funnel is filled up with snow4 ,a tin vessel of equal area to the funnel may at such times be useful as a substitute4 ,rain gauges are constructed of metal1 usually copper1 which1 besides being readily workable1 is little affected by atmospheric influences4 ,if made of iron or zinc1 they should be well japanned2 if of copper1 this is not so essential4 ,the capacity of a gauge should be sufficient to contain at least the probable maximum fall of rain in a day at the locality4 ,those required for rainy districts must be of large size4 #aah4 ,causes of ,rain4--,when the invisible vapour which is diffused in the atmosphere becomes sufficiently cooled1 it appears visible as mist or cloud1 and a further reduction of temperature causes its precipitation as rain1 hail1 or snow4 ,the cooling of the higher regions of the atmosphere is doubtless the chief cause of this condensation2 but the property which aqueous vapour possesses of radiating heat may also contribute to the result4 ,moreover1 the law which regulates the amount of vapour which air at any particular temperature can sustain in a transparent state1 determines that when two bodies of air at different temperatures1 saturated with vapour1 intermix1 some moisture must be rendered visible2 and hence1 it is not only possible1 but highly probable1 that rain may result from the conflict of different winds4 ,let us imagine two cubic yards of air1 both saturated with moisture1 but having the respective temperatures of #ej and #gj degrees1 to come into contact4 ,there will be a tendency to equalize the temperature to a mean1 which is #fj deg42 and during this process1 some of the vapour will be condensed4 ,for in the air at #ej deg4 there is #aaj4g grains of vapour#aa and #gj #baf4j ------ ,total amount of vapour #cbf4g ,but two cubic yards of air at #fj deg4 can only sustain #cac4b ------ ,hence there will be deposited #ac4e of rain4 ,it may be conceded1 therefore1 that when a warm and moist current of air encounters a body of cold air which may not be extremely dry1 the mixture is unable to retain the whole of the vapour in an invisible state2 so that the excess becomes visible as mist or fog1 and1 when the temperature has become sufficiently lowered1 rain4 ,the ,british ,isles are more or less enveloped in fog1 or mist1 at the commencement of easterly winds1 which1 with a sudden change of wind1 is exhibited even in summer2 while the south-westerly winds1 warm1 and arriving from the ocean1 deposit large quantities of rain by the cooling effect of the land1 colder by reason of its latitude4 ,when rain occurs with a northerly wind1 it is probably due to the deposition from an upper south-westerly current1 often apparently proved by the movements of the upper clouds4 #aai4 ,laws of ,rain-fall4--,tropical countries have a dry and a wet season during the year3 dry1 when the sun is at the opposite side of the equator2 wet1 when the sun is overhead4 ,with reference to the ,british ,isles1 the statistics collected by ,mr4 ,g4 ,j4 ,symons indicate that3 #ast4 ,the stations of least rain are inland1 or on the east or south-east coasts2 the stations of greatest rain are on the western coasts4 #bnd4 ,the rain-fall is very large in the vicinity of mountain chains or groups1 unless the station happens to be some miles to the north-eastward4 ,it may be well to illustrate these remarks by quoting#ab the average fall at a few places1 grouping them as-- ,westerly4 ,inches4 ,bodmin #dc ,bolton 7,lancashire7 #dd ,coniston 7,windermere7 #ga ,seathwaite #abg ,torosay 7,i4 of ,mull7 #ge ,killaloe 7,limerick7 #ch ,central4 ,inches4 ,enfield #bc ,epping #bc ,derby #bd ,york #bb ,stirling #ci ,perth #bi ,easterly4 ,inches4 ,witham 7,essex7 #ba ,patrington 7,hull7 #ba ,sunderland #ag ,inveresk 7,edinburgh7 #be ,pittenweem 7,fife7 #bd ,dublin #bb ,mr4 ,green1 the celebrated aeronaut1 has asserted from his experience1 that whenever a fall of rain happens1 and the sky is entirely overcast1 there will invariably be found to exist another stratum of cloud at a certain elevation above the former2 and the recent scientific balloon ascents by ,mr4 ,glaisher have tended to confirm this theory4 ,mr4 ,glaisher says1 ,it would seem to be an established fact1 that whenever rain is falling from an overcast sky1 there is a second stratum above4 ,it would also seem that when the sky is overcast without rain1 that there is no stratum of cloud above1 but that the sun is shining on the upper surface4 ,in every instance in which ,i have been up under these circumstances1 ,i have found such to be the case1 agreeing in this respect also with ,mr4 ,green's observations4 ,the amount of rain collected in a gauge placed near the surface of the earth is larger than in any gauge placed above it2 and the higher the gauge is placed1 the less water is collected4 ,mr4 ,glaisher contends that his balloon experiments corroborate this law4 #abj4 ,utility of ,statistics of ,rain-fall4--,the utility of knowing the rain-fall of any locality is sufficiently obvious1 and little need be said upon the subject4 ,the rain-gauge should be in the hands of every gardener and farmer4 ,in the management of out-door plants and crops1 as well as in the construction of cisterns and tanks for the supply of water1 a rain gauge is a valuable assistant4 ,by its use1 the gardener will be guided in judging how far the supply of moisture to the earth is needed2 and he will also see how beneficial is even a hasty shower to growing plants1 when he considers that a fall of rain measuring the tenth of an inch in depth1 corresponds to the deposit of about forty hogsheads per acre4 ,the study of the rain-fall of a country is of considerable interest to agriculturists4 ,the health and increase of domestic animals1 the development of the productions of the land1 as well as the daily labours of the farmer1 are dependent upon the excess or deficiency of rain4 ,it must be a subject of great satisfaction and confidence to the husbandman to know at the beginning of a summer1 by the certain evidence of meteorological results on record1 that the season1 in the ordinary course of things1 may be expected to be a dry and warm one2 or to find1 in a certain period of it1 that the average quantity of rain to be expected for the month has fallen4 ,on the other hand1 when there is reason1 from the same source of information1 to expect much rain1 the man who has courage to begin his operations under an unfavourable sky1 but with good ground to conclude1 from the state of his instruments and his collateral knowledge1 that a fair interval is approaching1 may often be profiting by his observations2 while his cautious neighbour who waited 'for the weather to settle' may find that he has let the opportunity go by4 ,this superiority1 however1 is attainable by a very moderate share of application to the subject2 and by the keeping of a plain diary of the barometer and rain-gauge1 with the hygrometer and vane1 under his daily notice4#ac ,the statistics of rain-fall are not only valuable and interesting in a meteorological point of view1 and for agricultural purposes1 but are also highly important in connection with sanitary arrangements for towns1 and engineering operations4 ,this is especially evident to the hydraulic engineer4 ,as rain is an important source of water-supply to rivers1 canals1 and reservoirs1 it is evident that a knowledge of the probable fall for any season or month1 at a given place1 as furnished by averages of the observations of former years1 will be the data upon which the engineer will base his plans for providing for floods or droughts2 while the measurement of the actual quantity which has just fallen1 as gathered from the indications of a series of gauges1 will suggest to him the precautions to adopt either to economise or conduct away the in-pouring waters4 ,when a canal is conducted across an undulating country1 its course is necessarily governed by the accidents of the ground1 and it alternately rises and falls4 ,in this case1 rising by a succession of levels1 it necessarily arrives at a certain highest level1 which is called by engineers the summit level4 ,from this it again descends by a corresponding series of levels4 ,now1 it is evident that1 supposing the locks to be all equal in magnitude1 the ascent of a vessel will require the descent of as much water from the summit to the lowest level as would fill a single lock2 for this quantity of water must be discharged from each lock of the series when the vessel passes through it4 ,the same may be said of the process by which the vessel descends along the series of locks on the other side of the summit4 ,it appears1 therefore1 that a supply of water must always be maintained on the summit level sufficient to fill a single lock twice for each vessel which crosses the summit4 ,it happens1 fortunately1 that by the laws of natural evaporation1 rain is precipitated in greater quantities on elevated summits than on the intermediate valleys1 so that the moving power1 in this case1 accommodates itself to the exigencies of intercommunication4--,dr4 ,lardner's ,handbook of ,natural ,philosophy4 #aba4 ,new ,form of ,rain-,gauge4--,since the foregoing pages were in type1 a modification of ,howard's rain-gauge has been arranged by ,mr4 ,symons1 which is compact in design1 convenient in use1 and low in price4 ,it combines the advantages of most gauges2 having solidity1 and facility of measurement4 ,the bottle is placed in a tin case1 to the bottom of which are attached stout spikes1 which1 when forced into the earth1 prevent its being upset either by wind or accident4 ,the bottle being transparent1 and slits made in the case1 the fall of rain is seen at a glance1 or with a race-glass1 from a window4 ,the funnel being attached to the cover of the case is thereby kept strictly horizontal1 and the depth of rain can be accurately measured by lifting the bottle from its case and emptying it into a graduated glass jar4 ,the funnel of this gauge is a very deep cone1 to prevent the rain drops outsplashing4 ,when properly placed1 the receiving surface will be twelve inches above the ground1 which experience has shown to be the most advantageous height4 ,,chapter ,,xiii4 ,,apparatus ,,employed ,,for ,,registering ,,the ,,direction1 ,,pressure1 ,,and ,,velocity ,,of ,,the ,,wind4 #abb4 ,the ,vane4--,the instrument by which the wind's direction is most generally noted1 is the vane1 or weather-cock1 and all that need be said of it here is that the points north1 east1 south and west1 usually attached to it1 should indicate the true and not the magnetic directions2 and that care should be taken to prevent its setting fast4 ,very complicated instruments are required for ascertaining the pressure and velocity of the wind1 and these are called ,anemometers4 ,the simplest is ,lind's4 ,illustration3 ,fig4 #hf4 #abc4 ,lind's ,anemometer1 or ,wind-,gauge 7fig4 #hf71 invented so late as #agge1 for showing the pressure of the wind1 consists of a glass syphon1 the limbs parallel to each other1 and each limb the same diameter4 ,one end of the syphon is bent at right angles to the limb1 so as to present a horizontal opening to the wind4 ,a graduated scale1 divided to inches and tenths1 is attached to the syphon tube1 reading either way from a zero point in the centre of the scale4 ,the whole instrument is mounted on a spindle1 surmounted by a vane1 and is moved freely in any direction by the wind1 always presenting the open end towards the quarter from which the wind blows4 ,to use the instrument1 it is simply filled up to the zero point with water1 and then exposed to the wind2 the difference in the level of the water gives the force of the wind in inches and tenths1 by adding together the amount of depression in one limb1 and elevation in the other1 the sum of the two being the height of a column of water which the wind is capable of sustaining at that time4 ,,table1 ,showing the ,force of ,wind on a square foot1 for different heights of the column of ,water in ,lind's ,wind-,gauge4 ----------------------------------- ,inches4,force in,common designation lbs4 of such ,wind4 --------------------------------- #f #ca4ge ,a ,hurricane4 #e #bf4jd ,a violent ,storm4 #d #bj4hc ,a great ,storm4 #c #ae4fb ,a ,storm4 #b #aj4db ,a strong ,wind4 #a #e4ba ,a high ,wind4 4#e #b4fj ,a brisk ,wind4 4#a 4#eb ,a fresh ,breeze4 4#je 4#bf ,a gentle ,breeze4 #j4 #j4 ,a ,calm4 ----------------------------------- #abd4 ,modification of ,lind's ,gauge4--,sir ,w4 ,snow ,harris has effected a modification of ,lind's anemometer1 with a view of obtaining a hand instrument for use at sea more especially4 ,at present the force of the wind is estimated at sea by an arbitrary scale1 suggested by ,sir ,f4 ,beaufort1 the late hydrographer2 #j being calm1 #ab the strongest hurricane1 and the intermediate numerals giving the varying strength of the wind4 ,there has been a long-felt want of instrumental means for obtaining this data at sea1 if merely for the sake of checking occasionally personal estimations1 which may vary considerably among different observers4 ,harris's wind gauge is intended to be held by hand1 while facing the wind1 and keeping it in proper position by attending to a spirit-level attached4 ,when in position1 and held firmly1 the tube has to be opened to the wind by pressure of the thumb acting upon jointed levers1 controlled by springs4 ,the pressure of the wind moves the enclosed liquid2 and by withdrawing the thumb1 the tube is closed so as to keep the liquid in its position2 the reading is then taken from its scale1 either in pounds on the square foot1 miles per hour1 or the ordinary designations of wind1 as light1 fresh1 strong1 c4 #abe4 ,robinson's ,anemometer4--,dr4 ,robinson1 of ,armagh1 is the inventor of a very successful anemometer1 which determines the horizontal velocity of the wind4 ,it was first used in #ahej1 in the meteorological and tidal observations made on the coast of ,ireland under the direction of the ,rev4 ,dr4 ,lloyd4 ,no meteorological observatory should be without this valuable instrument1 which is essential in determining the average velocity of the wind of a locality as distinguished from the most frequent wind of the same place4 ,it is represented in fig4 #hg4 ,four hollow hemispherical cups1 ,a ,a1 are extended upon conjugate diameters1 or arms1 with their diametrical planes placed vertically1 and facing the same way upon a vertical axis1 ,b1 which has at its lower extremity an endless screw1 ,d4 ,the axis is supported at ,c so as to turn with as little friction as possible4 ,the endless screw is placed in gear with a train of wheels and pinions4 ,each wheel carries an index over a stationary dial in front2 or the index is fixed1 and the graduations are placed upon the wheels themselves4 ,illustration3 ,fig4 #hg4 ,dr4 ,robinson has proved1 both by theory and experiment1 that the centre of any one of the cups so mounted and set in motion by the wind1 revolves with one-third of the wind's velocity4 ,if1 therefore1 the diametrical distance between the centres of the cups be one foot1 the circle described by the centres in one revolution is #c4adaf feet1 and the velocity of the wind will be three times this1 or #i4db feet1 which must be referred to time for the absolute rate4 ,the instrument is sometimes made with the centres of the cups #a4ab feet apart1 so that the circle described is #a_/aejj of a mile in circumference4 ,hence1 to produce one revolution of the cups1 the wind must travel three times as fast1 or #a_/ejj of a mile4 ,therefore1 #ejj revolutions will be produced by one mile of wind2 so that the dials may be graduated to register the velocity in miles and tenths of miles4 ,the simplest arrangement is with five dials1 recording respectively #aj1 #ajj1 #a1jjj1 #aj1jjj and #ajj1jjj revolutions4 ,directions for using ,robinson's ,anemometer4--,the dials read off in the same manner as the register of a gas meter1 commencing with the dial farthest from the endless screw4 ,the figures on the first dial indicate so many hundreds of thousands of revolutions2 those on the second dial so many tens of thousands2 those on the third1 thousands2 those on the fourth1 hundreds2 and those on the fifth so many tens4 ,the instrument should be read every morning at #i o'clock2 and1 usually1 it will only be necessary to read the first three dials4 ,the figures can be entered as they are read off4 ,should the index point between two figures1 the less of the two is to be taken4 ,for example1 if the first dial points to #g1 or between #g and #h2 while the second dial indicates #d2 and the third1 #e2 the entry to be made is #gde 7indicative of #gde thousand revolutions74 ,every time the index of the first dial is found to have passed zero 7#j71 a cross or star is to be prefixed to the next 7a lower7 reading4 ,to ascertain how many thousands of revolutions have been made during the month1 it will simply be necessary to subtract the first reading from the last1 and prefix to the three figures thus obtained a figure corresponding to the number of stars in the column4 ,for every thousand revolutions there are two miles of wind3 we have therefore only to multiply by #b to find how many miles of wind have passed during the month4 ,two entries must be made for the last day of each month 7the one being written under the other71 so as to bring the readings down to #i ,a4,m4 on the #ast of the following month4 ,the same entry which ends one month1 will therefore begin the next4 ,this repetition of one entry is necessary1 in order to prevent losing a day's wind4 ,the accompanying example of the #fhg readings of an ,anemometer for #ac days #ggc will illustrate the method of making #hbb the entries1 c4 #hee #ijj ,in this instance1 the first reading #iec 7#fhg7 is less than the last 7#gic74 #iij ,when the first reading is greater than 99#jff the last1 it will be necessary to borrow #aig #a1jjj in making the subtractions1 #cbc and then deduct one from the number #dad of stars4 ,thus1 if the first reading #eig of the series on the margin had #gab been #hhg1 the result would have been #gic #ijf instead of #aajf4 ---- #aajf thousands of revolutions4 #b ----- #ac #bbab miles of wind in period4 ----- #agj miles of wind per day1 on an average4 ,the foregoing directions are all which require to be regularly attended to4 ,but it may be interesting at times to find the velocity of the wind during a period of a few minutes4 ,this may be ascertained by observing the difference of two readings of all the dials1 with an interval of some minutes between them1 when a very brief calculation will suffice2 but perhaps the simplest method is the following3-- ,take two readings1 with an interval of #ab minutes between them4 ,the difference of these readings1 divided by #aj1 is the velocity of the wind in miles per hour4 ,thus--if the reading of the five dials 7from left to right7 at noon is #aebjf1 and at #ab minutes past #ab is #aecdh1 the velocity of the wind is #ad4b miles per hour4--,admiral ,fitz,roy1 ,f4,r4,s4 ,a lever and clutch are sometimes fitted to this anemometer1 as in fig4 #hh1 for throwing the train out of gear when not required to register4 ,it may also be connected with clock-work so as to be self-recording1 by causing the mechanism to impress a mark upon prepared paper moved by the apparatus1 at certain intervals of time4 ,illustration3 ,fig4 #hh4 ,this anemometer should be fixed in an exposed situation1 as high above ground as may be convenient for reading4 ,it may be made very portable1 by the arms which carry the cups being fitted to unscrew or to fold down4 ,when fitted in gimbals1 it can be used at sea with much advantage4 ,the pressure of the wind has been experimentally proved to vary as the square of the velocity2 the relation being ,v squared #bjj x ,p4 ,from this formula1 therefore1 the pressure can be calculated corresponding to the observed velocity4 #abf4 ,whewell's ,anemometer4--,this apparatus1 the invention of the celebrated ,dr4 ,w4 ,whewell1 registers the horizontal motion of the air with the direction4 ,its mechanism may be described in general terms1 as follows3-- ,a horizontal brass plate is attached to a vertical spindle1 which passes through the axis of a fixed cylinder1 being supported by a bearing at the lower end1 and working in a collar at the upper4 ,a vane is attached1 by which the plate is moved about according to the direction of the wind4 ,a fly1 having eight fans1 each fixed at an angle of #de deg4 with the axle1 is placed upon the plate so that the axle is in the line of direction of the vane4 ,an endless screw on the axle turns a vertical wheel having one hundred teeth1 the axle to which has also an endless screw working into a horizontal wheel1 having a like number of teeth1 and which communicates motion to a vertical screw fifteen inches long4 ,on this screw is placed a moveable nut1 which carries a pencil4 ,round the cylinder is wrapped daily a paper divided for the points of the compass4 ,the wind acting upon the vane will cause the plate to turn2 and the screw which carries the pencil will travel with it1 so that the pencil will mark upon the paper the direction of the wind4 ,the fly will also be set in motion1 and thereby the nut upon the screw will descend1 so that the attached pencil will trace a vertical line upon the paper4 ,when the fans on the axle are #b4c inches from axis to end1 and #a4i inches wide1 and the thread of the screw such that forty-five revolutions will cause the nut to descend two inches1 #ge4he miles of wind will cause the pencil to descend through a vertical space of two inches2 but the actual trace upon the paper will be longer in proportion to the magnitude of change of azimuth1 or direction1 of the wind4 #abg4 ,osler's ,anemometer1 and ,pluviometer4--,mr4 ,follet ,osler is the inventor of a self-recording apparatus which registers the direction and pressure of the wind1 and the amount and duration of rain1 upon the same sheet of paper4 ,his apparatus has met with very much approbation1 and has been erected in many observatories4 ,the mechanism may be modified in various ways1 and the following is a description of the simplest and most recent arrangement4 ,illustration3 ,fig4 #hi4 ,the instrument1 of which fig4 #hi is a diagram rather than a picture1 consists1 first1 of a vane1 ,v1 of a wedge-shape form1 which is found to answer better than a flat vane2 for the latter is always in a neutral line1 and therefore is not sufficiently sensitive4 ,a wind-mill governor has been substituted for the vane to get the direction of the wind1 with advantage4 ,at the lower end of the tube1 ,t ,t1 is a small pinion1 working in a rack1 r1 which moves backwards and forwards as the wind presses the vane4 ,to this rack a pencil1 x1 is attached1 which marks the direction of the wind on a properly ruled paper1 placed horizontally beneath1 and so adjusted as to progress at the rate of half an inch per hour1 by means of a simple contrivance connecting it with a good clock4 ,the paper is shown in the illustration upon the table of the instrument4 ,the pressure plate1 ,f1 for ascertaining the force of the wind1 is one foot square1 placed immediately beneath1 and at right angles with the vane2 it is supported by light bars1 running horizontally on friction rollers1 and communicating with flattened springs1 #a1 #b1 #c1 so that the plate1 when affected by the pressure of the wind1 acts upon them1 and they transfer such action to a copper chain passing down the interior of the direction tube1 and over a pulley at the bottom4 ,a light copper wire connects this chain with the spring lever1 y y1 carrying a pencil which records the pressure upon the paper below4 ,mr4 ,osler much prefers a spring to any other means for ascertaining the force of the wind1 because it is of the highest importance to have as little matter in motion as possible1 otherwise the momentum acquired will cause the pressure plate to give very erroneous indications4 ,the pressure plate is as light as is consistent with strength4 ,it is kept before the wind by the vane1 and is urged out by three or more springs1 so that with light winds one only is compressed1 and two1 or more1 according to the strength of the wind4 ,the pluviometer is placed on the right in the figure1 ,p ,p being the plane of the roof of the building4 ,the rain funnel1 ,r1 exposes an area of about #bjj square inches4 ,the water collected in it is conveyed by a tube through the roof of the building into a glass vessel1 ,g1 so adjusted and graduated as to indicate a quarter of an inch of rain for every #bjj square inches of surface1 i4 e4 #ej cubic inches4 ,g is supported by spiral springs1 b b1 which are compressed by the accumulating rain4 ,a glass tube1 open at both ends1 is cemented into the bottom of ,g1 and over it is placed a larger one closed at the top like a bell glass4 ,the smaller tube thus forms the long leg of a syphon1 and the larger tube acts as the short leg4 ,the water1 having risen to the level of the top of the inner tube1 drops over into a little copper tilt1 t1 in the globe1 ,s1 beneath the reservoir4 ,this tilt is divided into two equal partitions by a slip of copper1 and placed upon an axis not exactly balanced1 but so that one end or the other preponderates4 ,the water then drops into the end of the tilt which happens to be uppermost1 and when quite full it falls over1 throwing the water into the globe1 ,s1 from which it flows away by the waste pipe4 ,in this way an imperfect vacuum is produced in the globe1 quite sufficient to produce a draught in the small tube of the syphon1 or the long leg2 and the whole contents of the reservoir1 ,g1 immediately run off1 and the spiral springs1 b b1 elevate the reservoir to its original position4 ,to produce this action1 a quarter of an inch of rain must have fallen4 ,the registration is easily understood4 ,a spring lever1 z1 carrying a pencil1 is attached by a cord1 c1 to ,s4 ,this spring always keeps the cord tight1 so that as the apparatus descends during the fall of rain1 the spring advances the pencil more and more from the zero of the scale upon the paper beneath1 until a quarter of an inch has fallen1 when the pencil is drawn back to zero by the ascent of the reservoir4 ,the clock movement carries the registering paper forward by one of the wheels working into a rack attached to the frame4 ,the adjustment of the instrument should be carefully made at its first erection4 ,the scale for pressure should be established experimentally1 by applying weights of #b1 #d1 #f1 c41 lbs41 to move the pressure plate4 ,the registration trace for twenty-four hours is readily understood4 ,the direction is recorded on the centre part2 the pressure on one side1 and the rain on the other4 ,lines parallel to the length of the paper show no rain1 steady wind1 and constant pressure4 ,on the rain trace1 a line parallel to the width of the paper shows that the pencil had been drawn back to zero1 a quarter of an inch of rain having fallen4 ,the hour lines are in the direction of the width of the paper4 ,at the ,international ,exhibition #ahfb1 ,messrs4 ,negretti and ,zambra exhibited an improved ,osler's anemometer1 having combined with it ,robinson's cups1 so that the pressure and velocity appear on the same sheet1 on which a line an inch in length is recorded at every ten miles2 thus the complete instrument shows continuously the direction1 pressure1 and velocity of the wind4 #abh4 ,beckley's ,anemometer4--,mr4 ,r4 ,beckley1 of the ,kew ,observatory1 has devised a self-registering anemometer1 which consists of three principal parts3 ,robinson's cups for the determination of velocity2 a double fan1 or wind-mill governor1 for obtaining the direction2 and a clock to move a cylinder1 around which registration paper is wrapped4 ,the paper records the time1 velocity1 and direction of the wind for twenty-four hours1 when it must be replaced4 ,it has a cast-iron tubular support1 or pedestal to carry the external parts--the cups and the fans1--which must be erected upon the roof of the building upon which it is desired to mount the instrument4 ,the fans keep their axis at right angles to the wind2 and with any change of direction they move1 carrying with them an outer brass tube1 which rests upon friction balls on the top of the pedestal1 and is attached to a tubular shaft passing through the interior of the pedestal1 and terminating with a mitre wheel4 ,the mitre wheel1 working with other cogged wheels1 communicates the motion of the direction shaft to a cylinder carrying a pencil1 to record the direction4 ,the shaft carrying the cups is supported upon friction balls1 placed in a groove formed on the top of the direction shaft1 and passing through the interior of that shaft1 comes out below the mitre wheel1 where it is terminated in an endless screw1 or worm4 ,upon the wind moving the cups1 motion is given to the innermost shaft1 thence to the worm-wheel1 whence motion is given to a pencil which registers the velocity4 ,de la ,rue's metallic paper is used in registration1 it having the property of receiving a trace from a brass pencil4 ,the pencils can1 therefore1 be made in the most convenient form4 ,mr4 ,beckley forms each pencil of a strip of brass wrapped round a cylinder1 making a very thin threaded screw1 so that the contact of the pencil cylinder and the clock cylinder is a mere point of the metallic thread4 ,the pencil cylinders are placed side by side upon the cylinder turned by the clock1 and require no spring or other appliance to keep them to their work1 but always make contact with the registration paper by their own gravity4 ,they therefore require no attention1 and being as long as the trace which they make1 they will last a long time4 ,the velocity pencil has only one turn on the cylinder1 and its pitch is equal to a scale of fifty miles upon the paper4 ,the direction pencil has likewise one turn on its cylinder1 its pitch being equal to a scale of the cardinal points of the compass upon the paper4 ,the clock gives a uniform motion of half an inch per hour to the cylinder upon which the paper is fastened4 ,the registering mechanism of the instrument is very compact1 requiring only a space of about #ah inches by #h inches4 ,in the ,report of the ,british ,association for #aheh1 ,mr4 ,beckley has given a detailed description of his anemometer1 with drawings of all the parts4 #abi4 ,self-,registering ,lind's ,anemometer4--,a ,lind's wind-gauge1 designed to register the maximum pressure1 was exhibited at the ,international ,exhibition #ahfb1 by ,mr4 ,e4 ,g4 ,wood4 ,the bend of the syphon is contracted to obtain steadiness4 ,on the leeward limb a hole is drilled corresponding in size with the contracted portion of the tube4 ,the edge of the hole corresponds with the zero of the scale4 ,on the pressure of the wind increasing1 as much of the water as would have risen above the aperture flows away1 and therefore the quantity left indicates the greatest pressure of the wind since the last setting of the instrument1 which is done by filling it with water up to the zero point4 #acj4 ,anemometric ,observations4--,to illustrate the value of anemometric observations1 we quote from a paper by ,mr4 ,hartnup1 on the results obtained from ,osler's ,anemometer1 at the ,liverpool ,observatory4 ,the six years' observations1 ending #aheg1 gave for the yearly average of the winds3 ,north-easterly1 on #fj days1 at #g4h miles per hour2 ,north-westerly1 on #aab days1 at #ae4d miles per hour2 ,south-easterly1 on #aae days1 at #aa4j miles per hour2 ,south-westerly1 on #gg days1 at #ac4h miles per hour2 and one day calm4 ,from the same observations1 the average variation in the strength of the wind during the #bd hours is3--#aa miles per hour1 the minimum force1 occurring at #a-a_/b a4m42 until #f a4m4 it remains much the same1 being then #aa4c miles per hour2 at #aj a4m4 it is #ac4d miles per hour2 at #a-a_/b p4m4 the wind is at its maximum strength1 being #ad4h miles per hour2 at #e p4m4 it is again #ac4d miles per hour1 and at #i p4m4 #aa4c miles per hour4 ,hence it appears that the wind falls to its minimum force much more gradually than it rises to its maximum2 that the decrease and increase are equal and contrary1 so that the curve is symmetrical2 and that generally the force of wind is less at night than during the day4 ,there is evidence1 says ,admiral ,fitz,roy1 in ,mr4 ,hartnup's very valuable anemometrical results1 which seems to prove that to his observatory1 in a valley1 with buildings and hills to the north-eastward1 the real polar current does not blow from ,n4,e41 but nearer ,s4,e4 ,by his reliable digest of winds experienced there1 it appears that those most prevalent were from ,w4,n4,w4 and ,s4,s4,e4 ,but in ,england1 generally1 the prevailing winds are believed to be westerly1 inclining to south-westerly1 and north-easterly2 while of all winds1 the south-easterly is about the rarest4 ,at ,lord ,wrottesley's observatory1 in ,staffordshire1 about #ecj feet above the sea1 there appears to be considerably less strength of wind at any given time1 when a gale is blowing generally1 than occurs simultaneously at places along the sea-coast3 whence the inference is1 that undulations of the land's surface and hills1 diminish the strength of wind materially by frictional resistance4 ,all the synoptic charts hitherto advanced at the ,board of ,trade exhibit a marked diminution of force inland compared with that on the sea-coast4 ,indeed1 the coast itself offers similar evidence1 in its stunted1 sloping trees1 and comparative barrenness4#ad ,,chapter ,,xiv4 ,,instruments ,,for ,,investigating ,,atmospheric ,,electricity4 #aca4 ,atmospheric ,electroscope4--,the simplest instrument for ascertaining at any time the electric condition of the atmosphere is an electroscope composed of two equal pieces of gold leaf1 suspended from a brass support1 and insulated1 as well as protected from the movement of the air1 by a glass covering4 ,fig4 #ij represents such an instrument4 ,the cap of the brass support is fitted for the reception1 in the vertical direction1 of a metallic rod1 not less than two or three feet in length4 ,the top of the rod carries a clip4 ,the instrument acts according to the law1 that bodies similarly electrified repel each other2 but when dissimilarly electrified1 they attract each other4 ,to make an observation1 the instrument is placed in the open air1 and a lighted piece of cigar fusee1 or touch-paper1 is fixed in the clip4 ,the electricity of the air is collected by the substance undergoing combustion1 and conducted by the rod to the gold leaf2 and the pieces1 being similarly electrified1 separate more or less according to the amount of electricity present4 ,the kind is determined by the effect of either an excited stick of sealing-wax or rod of glass upon the electrified gold leaf4 ,a rod of glass1 when rubbed briskly with a silk handkerchief or piece of woollen cloth1 becomes positively electrified1 or excited1 as it is termed4 ,a stick of sealing-wax1 similarly treated1 acquires the negative state4 ,if1 therefore1 an excited glass rod be presented to the cap of the instrument1 and it cause the pieces of gold leaf to diverge still further1 the electric state of the air must be analogous to that of the glass1 that is1 positive2 if they approach1 it is negative4 ,on the contrary1 if a stick of sealing-wax be used1 the pieces will be repelled more apart if they have acquired negative electricity from the air2 and they will converge if they have a positive charge4 ,illustration3 ,fig4 #ij4 ,by means of this very simple instrument1 meteorological observers can readily ascertain the electric condition of the lower air at any time4 ,,note4--,a book containing strips of gold leaf is sent with the ,electrometer to replace the gold leaves when torn or broken in use4 ,to mount fresh gold leaves1 unscrew the brass plate to which is attached the rod supporting the leaves2 then moisten with the breath the flat piece of brass1 and press it gently down on one strip of gold1 whilst the book is only partly opened2 the second leaf is attached in the same manner4 #acb4 ,volta's ,electrometer is similar to the instrument just described1 except that instead of gold leaf two light pieces of straw1 or two pith balls1 are freely suspended from the conductor2 the amount of the electric charge being estimated from the degrees of divergence1 shown by a graduated arc4 #acc4 ,peltier's ,electrometer is a much superior instrument in point of sensibility4 ,a tall glass tube an inch or more in diameter1 is connected to a glass receiver1 mounted on a base fitted with levelling screws4 ,at the top of the tube is formed a globe from four to five inches in diameter1 which is thickly gilt on the exterior1 so as to form a good conducting surface4 ,a wire passes from the ball down the tube into the receiver1 where it is bent up1 and ends in a steel point over the centre of the base4 ,a bent wire1 carrying a small magnetic needle1 is balanced on the steel point1 so that the magnet1 with the fine wire1 arranges itself horizontally in the direction of the magnetic meridian4 ,if any cloud or portion of air in the neighbourhood be in an electrical state1 it will act by induction upon the gilt ball1 and the needle will be deflected from its north and south direction4 ,a graduated circle indicates the number of degrees of the deflection1 which will be greater or less according to the tension of the electricity4 ,to ascertain whether the electricity is positive or negative1 a stick of shellac or glass must be employed1 as already described4 #acd4 ,bohnenberger's ,electroscope may be fitted with a metallic conductor1 and used with great advantage for observing atmospheric electricity4 ,the principal parts of the instrument1 as improved by ,becquerel1 are the following3--,a ,b1 fig4 #ia1 is a small dry galvanic pile of from #ejj to #hjj pairs1 about a quarter of an inch in diameter2 when the plates are pressed together1 such a pile will be from #b to #b-a_/b inches in length4 ,the wires1 which are bent so as to stand above the pile1 terminate in two plates1 ,p and ,m1 which are the poles of the pile4 ,these plates1 which are #b inches by #a_/b an inch1 are parallel and opposite to each other4 ,it is convenient for their opposite sides to be slightly convex1 for them to be gilded or coated with platinum1 and for them to run on the polar wires1 by the latter being made to pass through a small hole in them4 ,one of these plates will always be in a state of positive1 and the other of negative1 electricity2 between them suspend the very fine gold leaf1 ,d ,g1 which is attached to the conductor1 ,c ,d1 of copper wire4 ,if the leaf hang exactly between the two plates1 it is equally attracted by each1 and will therefore be in a state of repose4 ,the apparatus should be protected by a bell-glass1 fitting exactly1 and having an opening at the top through which the copper wire1 ,c ,d1 passes2 the wire1 however1 is insulated by its being contained in a glass tube1 which is made to adhere to the bell-glass by means of a small portion of shellac or gum-lac4 ,screw on a metal ball or plate1 to impart to it the electricity you wish to test1 which will be conveyed by the copper wire to the gold leaf1 and the latter will immediately move towards the plate which has the opposite polarity4 ,this electroscope is1 beyond doubt1 one of the most delicate ever constructed1 and is well adapted to show small quantities of positive and negative electricity4 ,illustration3 ,fig4 #ia4 ,to ensure the susceptibility of electroscopes and electrometers placed under bell-glasses1 precautions should be taken to render the air they contain as dry as possible1 which may be effected by enclosing in a suitable vessel a little melted chloride of calcium beneath the glass4 ,the galvanic pile employed in this electroscope is that invented by ,zamboni4 ,it differs from the common hydro-electric batteries principally in this1 that the presence of the electromotive liquid is dispensed with1 and that in its place is substituted some moist substance of low conducting power1 generally paper4 ,the electromotors in these piles are composed for the most part of ,dutch gold 7copper7 and silver 7zinc7 paper pressed one on the other1 with their paper sides together1 out of which discs are cut with a diameter of from a quarter of an inch to an inch4 ,more powerful pairs of plates may be obtained by using only the silver paper and smearing its paper side with a thin coat of honey1 on which some finely pulverized peroxide of manganese has been sprinkled1 and all the sides similarly coated are presented one way4 ,powerful pairs of plates may also be made by pasting pure gold leaf on the paper side of zinc-paper4 ,these plates are then to be arranged1 just as in the ordinary voltaic pile1 one above the other1 so that the similar metallic surfaces may all lie one way2 press them tightly together2 tie them with pretty stout silk threads1 and press them into a glass tube of convenient size4 ,the metal rims of the tubes1 which must be well connected with the outermost pairs of plates1 form the poles of the pile1 the negative pole being in the extreme zinc surface1 and the positive in the extreme copper or manganese surface4 ,the electromotive energy called into action in these dry piles is less than that excited in the moist or hydro-electric piles1 principally on account of the imperfect conduction of the paper4 ,the accumulation of electricity at their poles also goes on less rapidly1 and consequently the electrical tension continues for a long while unaltered2 whereas1 in all moist piles1 even in the most constant of them1 the tension is maintained1 comparatively speaking1 for but a short time1 on account of the chemical action and decomposition of the electromotive fluid--causes of disturbance which do not exist in the dry pile4#ae #ace4 ,thomson's ,electrometer4--,professor ,w4 ,thomson1 of ,glasgow1 has devised an atmospheric electrometer1 which is likely to become eminently successful1 in the hands of skilful observers4 ,it is mainly a torsion balance combined with a ,leyden-jar4 ,the index is an aluminium needle strung on a fine platinum wire1 passing through its centre of gravity1 and stretched firmly between two points4 ,the needle and wire are carefully insulated from the greater part of the instrument1 but are in metallic communication with two small plates fixed beside the two ends of the needle1 and termed the repelling plates4 ,a second pair of larger plates face the repelling plates1 on the opposite side of the needle1 but considerably farther from it4 ,these plates are in connection with the inner coating of a ,leyden-jar1 and are termed the attracting plates4 ,the whole instrument is enclosed in a metal cage1 to protect the glass ,leyden-jar and the delicate needle4 ,the ,leyden-jar should be charged when the instrument is used4 ,its effect is two-fold3 it increases greatly the sensibility of the instrument1 and enables the observer to distinguish between positive and negative electrification4 ,the air inside the jar is kept dry by pumice-stone1 slightly moistened with sulphuric acid2 by which means very perfect insulation is maintained4 ,electrodes1 or terminals1 are brought outside the instrument1 by which the ,leyden-jar can be charged1 and the needle system connected with the body1 the electric state of which is to be tested4 ,for the purpose of testing the electric state of the atmosphere1 the instrument is provided with a conductor and support for a burning match1 or1 preferably1 with an arrangement termed a water-dropping collector2 by either of which means the electricity of the air is conveyed to the needle system4 ,the needle abuts upon the repelling plates when not influenced by electricity1 in which position it is at zero4 ,it can always be brought back to zero by a torsion-head1 turning one end of the platinum wire1 but insulated from it1 and provided with a graduated circle1 so that the magnitude of the arc1 that the torsion-head is moved through to bring the needle to zero1 measures the force tending to deflect it4 ,the action of the instrument is as follows3--,the ,leyden-jar is to be highly charged1 say negatively2 and the repelling plates are to be connected with the earth4 ,the needle will then be deflected against a stop1 under the combined influence of attraction from the ,leyden-jar1 or attracting plates1 and repulsion from the repelling plates due to the positive charge induced on the needle and its plates by the ,leyden-jar plates4 ,the platinum wire must then be turned round by the torsion-head so as to bring back the needle to zero2 and the number of degrees of torsion required will measure the force with which the needle is attracted4 ,next1 let the needle plates be disconnected from the earth1 and connected with the insulated body1 the electric state of which is to be tested4 ,in testing the atmosphere1 the conductor and lighted match1 or water-dropping apparatus1 must be applied4 ,if the electricity of the body be positive1 it will augment the positive charge in the needle plates1 induced by the ,leyden-jar plates2 and consequently the needle will be more deflected than by the action of the jar alone4 ,if the electricity of the body be negative1 it will tend to neutralize the positive charge2 and the needle will be less deflected4 ,hence the kind of electricity present in the air becomes at once apparent1 without the necessity of an experimental test4 ,the platinum wire must then be turned till the needle is brought to zero1 and the number of degrees observed2 which is a measure of the intensity of the electrification4 ,any loss of charge from the ,leyden-jar which may from time to time occur1 reducing the sensibility inconveniently1 may be made good by additions from a small electrophorus which accompanies the instrument4#af ,the instrument may be made self-recording by the aid of clockwork and photography4 ,to effect this1 a clock gives motion to a cylinder1 upon which photographic paper is mounted4 ,the needle of the electrometer is made to carry a small reflector2 and rays from a properly adjusted source of light are thrown by the reflector1 through a small opening1 upon the photographic paper4 ,it is evident1 that as the cylinder revolves1 a trace will be left upon the paper1 showing the magnitude of1 and variations in1 the deflection of the needle4 #acf4 ,fundamental ,facts regarding ,atmospheric ,electricity4--,the general electrical condition of the atmosphere is positive in relation to the surface of the earth and ocean1 becoming more and more positive as the altitude increases4 ,when the sky is overcast1 and the clouds are moving in different directions1 it is subject to great and sudden variations1 changing rapidly from positive to negative1 and the reverse4 ,during fog1 rain1 hail1 sleet1 snow1 and thunderstorms1 the electrical state of the air undergoes many variations4 ,the intensity of the electricity increases with hot weather following a series of wet days1 or of wet weather coming after a continuance of dry days4 ,the atmospheric electricity1 in fact1 seems to depend for its intensity and kind upon the direction and character of the prevailing wind1 under ordinary circumstances4 ,it has an annual and a diurnal variation4 ,there is a greater diurnal change of tension in winter than in summer4 ,by comparing observations from month to month1 a gradual increase of tension is perceived from ,july to ,february1 and a decrease from ,february to ,july4 ,the intensity seems to vary with the temperature4 ,the diurnal variation exhibits two periods of greatest and two of least intensity4 ,in summer1 the maxima occur about #aj a4m4 and #aj p4m42 the minima about #b a4m4 and noon4 ,in winter1 the maxima take place near #aj a4m4 and #h p4m42 the minima near #d a4m4 and #d p4m4 ,the researches of ,saussure1 ,beccaria1 ,crosse1 ,quetelet1 ,thompson1 and ,fitz,roy have tended to show that during the prevalence of polar currents of air positive electricity is developed1 and becomes more or less active according to the greater or less coldness and strength of wind2 but with winds from the equatorial direction there is little evidence of sensitive electricity1 and when observable1 it is of the negative kind4 ,storms and gales of wind are generally attended1 in places1 with lightning and thunder2 and as the former are very often attributed to the conflict of polar and equatorial winds1 the difference of the electric tension of these winds may account for the latter phenomena4 ,it is not our intention to enter upon the general consideration of thunderstorms2 the facts which we have given may be of service to the young observer2 and finally1 as it is interesting to be able to judge of the locality of a thunderstorm1 the following simple rule will be of service1 and sufficiently accurate3--,note by a second's watch the number of seconds which elapse from the sight of the lightning to the commencement of the thunder2 divide them by five1 and the quotient will be the distance in miles4 ,thus1 if thunder is heard ten seconds after the lightning was seen1 the distance from the seat of the storm will be about two miles4 ,the interval between the flash and the roll has seldom been observed greater than seventy-two seconds4 #acg4 ,lightning ,conductors4--,the line of danger1 whether from the burning or lifting power of lightning1 is the line of strong and obstructed currents of air1 of the greatest aerial friction4#ag ,trees1 church spires1 wind-mills and other tall structures1 obstruct the aerial currents1 and hence their exposure to danger4 ,the highest objects of the landscape1 especially those that are nearest the thunder cloud1 will receive the lightning stroke4 ,the more elevated the object1 the more likely is it to be struck4 ,of two or more objects1 equally tall and near1 the lightning is invariably found to select the best conductor of electricity1 and even to make a circuitous path to get to it4 ,hence the application and evident advantage of metallic rods1 called lightning conductors1 attached to buildings and ships4 ,a lightning conductor should be pointed at top1 and extend some feet above the highest part of the edifice1 or mast4 ,it should be made of copper1 which is a better conducting medium than iron1 and more durable1 being less corrosive4 ,it must be unbroken throughout its length1 and extend to the bottom of the building1 and even some distance into the ground1 so as to conduct the electricity into a well or moist soil4 ,if it be connected with the lead and iron work in the structure of the house1 it will be all the better1 as affording a larger surface1 and a readier means of exit for the fluid4 ,in a ship1 the lower end of the conductor should be led into communication with the hull1 if of iron1 and with the copper sheathing1 if a wooden vessel2 so that1 spread over a large surface1 it may escape more readily to the water4 #ach4 ,precautions against ,lightning4--,experience seems to warrant the assumption that any building or ship1 fitted with a substantial lightning conductor1 is safe from danger during a thunderstorm4 ,should a house or vessel be undefended by a conductor1 it may be advisable to adopt a few precautions against danger4 ,in a house1 the fire-place should be avoided1 because the lightning may enter by the chimney1 its sooty lining being a good conductor4 ,through chimneys1 lightning has a way into most houses2 and therefore1 it is wise1 by opening doors or windows1 to give it a way out4 ,wherever the aerial current is fiercest1 there the danger is greatest2 and if we kept out of the way of currents or draughts1 we keep out of the way of the lightning4#ah ,lightning evinces as it were a preference for metallic substances1 and will fly from place to place1 even out of the direct line of its passage to the earth1 to enter such bodies4 ,it is therefore well to avoid1 as much as possible1 gildings1 silvered mirrors1 and articles of metal4 ,the best place is perhaps the middle of the room1 unless a draught passes1 or a metallic lamp or chandelier should be hanging from the ceiling4 ,the neighbourhood of bad conductors1 such as glass windows1 not being open1 and on a thick bed of mattrasses1 are safe places4 ,the quality of trees as lightning conductors is considered to depend upon their height and moisture1 those which are taller and relatively more humid being struck in preference to their fellows2 therefore1 it is unwise to seek shelter under tall and wet trees during a thunderstorm4 ,in the absence of any other shelter1 it would be better to lie down on the ground4 ,,chapter ,,xv4 ,,ozone ,,and ,,its ,,indicators4 #aci4 ,nature of ,ozone4--,during the action of a powerful electric machine1 and in the decomposition of water by the voltaic battery1 a peculiar odour is perceptible1 which is considered to arise from the generation of a substance to which the term ozone has been given1 on account of its having been first detected by smell1 which1 for a long time after its discovery1 was its only known characteristic4 ,a similar odour is evolved by the influence of phosphorus on moist air1 and in other cases of slow combustion4 ,it is also traceable1 by the smell1 in air1--where a flash of lightning has passed immediately before4 ,afterwards it was established that the same element possessed an oxidising property4 ,it was found to be liberated at the oxygen electrode when water was decomposed by an electric current2 and has been regarded by some chemists as what is termed an allotropic form of oxygen1 while others speak of it as oxygen in the nascent state1 and some even regard it as intimately related to chlorine4 ,so various are the existing notions of the nature of this obscure agent4 ,its oxidising property affords a ready means for its detection1 even when the sense of smell completely fails4 ,the methods of noting the presence and measuring the amount of ozone present in the air1 are very simple2 being the free exposure to the air1 defended from rain and the direct rays of the sun1 of prepared test-papers4 ,there are two kinds of test-papers4 ,one kind was invented by ,dr4 ,schonbein1 the original discoverer of ozone2 and the other1 which is more generally approved1 by ,dr4 ,moffat4 #adj4 ,schonbein's ,ozonometer consists of strips of paper1 previously saturated with a solution of starch and iodide of potassium1 and dried4 ,the papers are suspended in a box1 or otherwise properly exposed to the air1 for a given interval1 as twenty-four hours4 ,the presence of ozone is shown by the test-paper acquiring a purple tint when momentarily immersed in water4 ,the amount is estimated by the depth of the tint1 according to a scale of ten tints furnished for the purpose1 which are distinguished by numbers from #a to #aj4 ,the ozone decomposes the compound which iodine forms with hydrogen1 and1 it is presumed1 combines as oxygen with hydrogen1 while the iodine unites with the starch1 giving the blue colour when moist4 #ada4 ,dr4 ,moffat's ,ozonometer consists of papers prepared in a somewhat similar manner to ,schonbein's2 but they do not require immersion in water4 ,the presence of ozone is shown by a brown tint1 and the amount by the depth of tint according to a scale of ten tints1 which is furnished with each box of the papers4 ,moffat's have the advantage of preserving their tint for years1 if kept in the dark1 or between the leaves of a book2 and are simpler to use4 ,illustration3 ,fig4 #ib4 #adb4 ,sir ,james ,clark's ,ozone ,cage 7fig4 #ib71 consists of two cylinders of very fine wire gauze1 one fitting into the other2 the wire gauze being of such a fineness as to permit the free ingress of air1 at the same time that it shuts out all light that would act injuriously on the test-paper1 which is suspended by a clip or hook attached to the upper part of the inner cylinder4 #adc4 ,distribution and ,effects of ,ozone4--,mr4 ,glaisher has found that the amount of ozone at stations of low elevation is small2 at stations of high elevation1 it is almost always present2 and at other and intermediate stations1 it is generally so4 ,the presence and amount of ozone would seem to be graduated by the elevation1 and to increase from the lowest to the highest ground4 ,the amount of ozone is less in towns than in the open country at the same elevation2 and less at inland than at sea-side stations4 ,it seems to abound most with winds from the sea1 and to be most prevalent where the air is considered the purest and most salubrious4 ,this may seem1 says ,admiral ,fitz,roy1 in ,the ,weather ,book1 to point to a connection between ozone and chlorine gas1 which is in and over sea-water1 and which must be brought by any wind that blows from the sea4 ,it prevails more over the ocean and near it than over land1 especially land remote from the sea2 and1 says the ,admiral1 it affects the gastric juice1 improves digestion1 and has a tanning effect4 ,dr4 ,daubeny1 in his ,lectures on ,climate1 writes3 ,its presence must have a sensible influence upon the purity of the air1 by removing from it foetid and injurious organic effluvia4 ,it is also quite possible that ozone may play an important part in regulating the functions of the vegetable kingdom likewise2 and although it would be premature at present to speculate upon its specific office1 yet1 for this reason alone1 it may be well to note the fact of its frequency1 in conjunction with the different phases which vegetation assumes1 persuaded that no principle can be generally diffused throughout nature1 as appears to be the case1 with this1 without having some important and appropriate use assigned for it to fulfil4 #add4 ,registering ,ozonometer4--,dr4 ,e4 ,lancaster has contrived an ozonometer1 the object of which is to secure the constant registration of ozone1 so that the varying quantities present in the atmosphere may be detected and registered4 ,for this purpose1 an inch of ozone paper passes in each hour1 by clock-work1 beneath an opening in the cover of the instrument4 ,,chapter ,,xvi4 ,,instruments ,,not ,,described ,,in ,,the ,,preceding ,,chapters4 #ade4 ,chemical ,weather ,glass4--,this curious instrument appears to have been invented more than a hundred years ago1 but the original maker is not known4 ,it is simply a glass vial about ten inches long and three quarters of an inch in diameter1 which is nearly filled1 and hermetically sealed1 with the following mixture3--,two drachms of camphor1 half a drachm of nitrate of potassium1 half a drachm of chlorate of ammonium1 dissolved in about two fluid ounces of absolute alcohol mixed with two ounces of distilled water4 ,all the ingredients should be as pure as possible1 and each vial filled separately4 ,when the instruments are made in numbers and filled from a common mixture1 some get more than the due proportion of the solid ingredients1 and consequently such glasses do not exhibit that uniformity of appearance and changes1 that undoubtedly should accompany similar influencing circumstances4 ,it is in consequence of a want of precision and fixed principle of manufacture1 that these interesting instruments are not properly appreciated1 and more generally used4 ,the glass should be kept quite undisturbed1 exposed to the north1 and shaded from the sun4 ,camphor is soluble in alcohol1 but not in water1 while both water and alcohol have different solvent powers1 according to the temperature2 hence1 the solid ingredients being in excess for certain conditions of solution1 depending upon temperature chiefly1 and perhaps electricity and the action of light also1 appear as crystals and disappear with the various changes that occur in the weather4 ,the various appearances thus presented in the menstruum have been inferred to prognosticate atmospheric changes4 ,the following rules have been deduced from careful study of the glass and weather3-- #a4 ,during cold weather1 beautiful fern-like or feathery crystallization is developed at the top1 and sometimes even throughout the liquid4 ,this is the normal state of the glass during winter4 ,the crystallization increases with the coldness2 and if the structure grows downward1 the cold will continue4 #b4 ,during warm and serene weather1 the crystals dissolve1 the upper and greater part of the liquid becoming perfectly clear4 ,this is the normal state of the glass during summer4 ,the less amount of crystallization1 that is1 the greater the clear portion of the liquid 7for there is always some of the composition visible at the bottom71 the greater the probability of continued fine dry weather4 #c4 ,when the upper portion is clear1 and flakes of the composition rise to the top and aggregate1 it is a sign of increasing wind and stormy weather4 #d4 ,in cold weather1 if the top of the liquid becomes thick and cloudy1 it denotes approaching rain4 #e4 ,in warm weather1 if small crystals rise in the liquid1 which still maintains its clearness1 rain may be expected4 #f4 ,sharpness in the points and features of the fern-like structure of the crystals1 is a sign of fine weather2 but when they begin to break up1 and are badly defined1 unsettled weather may be expected4 ,admiral ,fitz,roy1 in ,the ,weather ,book1 writes of this instrument as follows3--,since #ahbe1 we have generally had some of these glasses1 as curiosities rather than otherwise2 for nothing certain could be made of their variations until lately1 when it was fairly demonstrated that if fixed undisturbed in free air1 not exposed to radiation1 fire1 or sun1 but in the ordinary light of a well-ventilated room1 or1 preferably1 in the outer air1 the chemical mixture in a so-called storm-glass varies in character with the direction of the wind--not its force1 specially 7though it may so vary in appearance1 only from another cause1 electrical tension74 ,as the atmospheric current veers toward1 comes from1 or is only approaching from the polar direction1 this chemical mixture--if closely1 even microscopically watched--is found to grow like fir1 yew1 fern leaves1 or hoar-frost--or like crystallizations4 ,as the wind1 or great body of air1 tends more from the opposite quarter1 the lines or spikes--all regular1 hard1 or crisp features--gradually diminish1 till they vanish4 ,before1 and in a continued southerly wind1 the mixture sinks slowly downward in the vial1 till it becomes shapeless1 like melting white sugar4 ,before1 or during the continuance of a northerly wind 7polar current71 the crystallizations are beautiful 7if the mixture is correct1 the glass a fixture1 and duly placed72 but the least motion of the liquid disturbs them4 ,when the main currents meet1 and turn toward the west1 making easterly winds1 stars are more or less numerous1 and the liquid dull1 or less clear4 ,when1 and while they combine by the west1 making westerly winds1 the liquid is clear1 and the crystallization well-defined1 without loose stars4 ,while any hard or crisp features are visible below1 above1 or at the top of the liquid 7where they form for polar winds71 there is plus electricity in the air2 a mixture of polar current co-existing in that locality with the opposite1 or southerly4 ,when nothing but soft1 melting1 sugary substance is seen1 the atmospheric current 7feeble or strong as it may be7 is southerly with minus electricity1 unmixed with1 and uninfluenced by1 the contrary wind4 ,repeated trials with a delicate galvanometer1 applied to measure electric tension in the air1 have proved these facts1 which are now found useful for aiding1 with the barometer and thermometer1 in forecasting weather4 ,temperature affects the mixture much1 but not solely2 as many comparisons of winter with summer changes of temperature have fully proved4 ,a confused appearance of the mixture1 with flaky spots1 or stars1 in motion1 and less clearness of the liquid1 indicates south-easterly wind1 probably strong to a gale4 ,clearness of the liquid1 with more or less perfect crystallizations1 accompanies a combination1 or a contest1 of the main currents1 by the west1 and very remarkable these differences are1--the results of these air currents acting on each other from eastward1 or from an entirely opposite direction1 the west4 ,the glass should be wiped clean now and then1--and once or twice a year the mixture should be disturbed1 by inverting and gently shaking the glass vial4 ,illustration3 ,fig4 #ic4 #adf4 ,leslie's ,differential ,thermometer4--,a glass tube having a large bulb at each extremity1 and bent twice at right angles1 as represented in figure #ic1 containing strong sulphuric acid tinged with carmine1 and supported at the centre by a wooden stand1 constitutes the differential thermometer as invented by ,professor ,leslie4 ,the instrument is designed to exhibit and measure small differences of temperature4 ,each leg of the instrument is usually from three to six inches long1 and the balls are about four inches apart4 ,the calibre of the legs is about #a_/ej inch1 not more2 the other part of the tube may be wider4 ,the tube is filled with the liquid1 the bulbs contain air4 ,when both bulbs are heated alike1 each scale indicates zero4 ,the scale is divided so that the space between the freezing and the boiling-points of water is equal to #a1jjj parts4 ,when one bulb is heated more than the other1 the difference of temperature is delicately shown by the descent of the coloured fluid from the heated ball4 ,it is uninfluenced by changes in the temperature of the atmosphere2 hence it is admirably adapted for experiments of radiant heat4 ,the theory of the instrument is that gases expand equally for uniform increments of heat4 #adg4 ,rumford's ,differential ,thermometer differs from that just described in simply containing only a small bubble of liquid1 which lies in the centre of the tube1 when both bulbs are similarly influenced4 ,the bulbs and other parts of the tube contain air4 ,when one bulb is more heated than the other1 the bubble moves towards the one less heated2 and the scale attached to the horizontal part of the tube affords a measurement of the difference of temperature4 ,illustration3 ,fig4 #id4 #adh4 ,glaisher's ,thermometer ,stand4--,the thermometer stand consists of a horizontal board as a base1 of a vertical board projecting upwards from one edge of the horizontal one1 and of two parallel inclined boards1 separated from each other by blocks of three inches in thickness1 connected at the top with the vertical1 and at the bottom with the horizontal board1 and the air passes freely about and between them all4 ,to the top of the inclined boards is connected a small projecting roof to prevent the rain falling on the bulbs of the instrument1 which are carried on the face of the vertical board1 with their bulbs projecting below it1 so that the air plays freely on the bulbs from all sides4 ,the whole frame revolves on an upright post firmly fixed to the ground1 as shown in the engraving1 fig4 #id2 and in use1 the inclined side is always turned towards the sun4 #adi4 ,thermometer ,screen1 for use at ,sea4--,this screen1 or shade1 was designed by ,admiral ,fitz,roy1 and has been in use for several years on board ,h4,m4 vessels and many merchant-ships4 ,it is about twenty-four inches long by twelve wide and eight deep2 having lattice-work sides1 door1 and bottom2 with perforation also at top1 so contrived that the air has free access to the interior1 while the direct rays of the sun1 rain1 and sea spray are effectually excluded from the thermometers mounted inside4 ,there is ample space for two thermometers placed side by side on brackets1 at least three inches from each other or any part of the exterior of the screen4 ,one thermometer should be fitted up as a wet bulb 7see p4 #aje74 ,a small vessel of water can easily be fixed inside the screen so as to retain its position and contents under the usual motions of the ship2 and by means of a piece of cotton-wick1 or muslin rag tied round the bulb of the thermometer and trailing into the cup of water1 keep the bulb constantly moist4 ,self-registering thermometers should be protected by a similar screen4 ,it has been found that thermometric observations made at sea are not valuable for scientific purposes unless the instruments have been duly protected by such a screen4 #aej4 ,anemoscope1 or ,portable ,wind ,vane for travellers1 with compass1 bar needle1 c41 shows the direct course of the wind to half a point of the compass4 ,illustration3 ,fig4 #ie4 #aea4 ,evaporating ,dish1 or ,gauge 7fig4 #ie71 for showing the amount of evaporation from the earth's surface4 ,this gauge consists of a brass vessel1 the area or evaporating surface of which is accurately determined2 and also a glass cylindrical measure1 graduated into inches1 tenths1 and hundredths of inches4 ,in use1 the evaporating gauge is nearly filled with water1 the quantity having been previously measured by means of the glass cylinder2 it is then placed out of doors1 freely exposed to the action of the atmosphere2 after exposure1 the water is again measured1 and the difference between the first and second measurement shows the amount of evaporation that has taken place4 ,if rain has fallen during the exposure of the gauge1 the quantity collected by it must be deducted from the measured quantity2 the amount is shown by the quantity of rain collected in the rain gauge4 ,the wire cage round the gauge is to prevent animals1 birds1 c41 from drinking the water4 #aeb4 ,dr4 ,babington's ,atmidometer1 or instrument for measuring the evaporation from water1 ice or snow1 consists of an oblong hollow bulb of glass or copper1 beneath which and communicating with it by a contracted neck is a second globular bulb1 duly weighted with mercury or shot4 ,the upper bulb is surmounted by a small glass or metal stem1 having a scale graduated to grains and half-grains2 on the top of which is fixed horizontally a shallow metal pan4 ,the bulbs are immersed in a vessel of water having a circular hole in the cover through which the stem rises4 ,distilled water is then gradually poured into the pan above1 until the zero of the stem sinks to a level with the cover of the vessel4 ,thus adjusted1 as the water in the pan evaporates1 the stem ascends1 and the amount of evaporation is indicated in grains4 ,this instrument affords a means of measuring evaporation from ice or snow4 ,an adjustment for temperature is necessary4 #aec4 ,cloud ,reflector4--,at the ,international ,exhibition #ahfb1 ,mr4 ,j4 ,t4 ,goddard exhibited a cloud mirror1 for ascertaining the direction in which the clouds are moving4 ,the mirror is laid on a horizontal support near a window1 and fastened so that the point marked north may coincide with the south point of the horizon1--the several points will consequently be reversed4 ,the edge of a conspicuous cloud is brought to the centre of the mirror1 and the observer keeps perfectly still until it passes off at the margin1 where the true point of the horizon from which the clouds are coming can be read off4 #aed4 ,sunshine ,recorder4--,mr4 ,goddard also exhibited an instrument which he calls by this name4 ,it works by letting the sun's rays pass through a narrow slit1 and fall on photographic paper wound round a barrel moved by clock-work2 the paper being changed daily1 and the photographic impression developed and fixed in the usual manner4#ai #aee4 ,,set ,,of ,,portable ,,instruments4 ,in a small box1 #h in4 by #h in4 by #d in41 a complete set of meteorological instruments have been packed4 ,the lid of the box1 by an ingenious arrangement1 is made to take off and hang up2 on it are permanently fixed for observation1 a maximum and minimum1 and a pair of dry and wet bulb thermometers4 ,the interior of the box contains a maximum thermometer in vacuo for solar radiation1 and a minimum for terrestrial purposes1 one of ,negretti and ,zambra's small pocket aneroid barometers1 pedometer for measuring distances1 pocket compass1 clinometer1 and lastly a rain gauge4 ,this latter instrument consists of an accurately turned brass ring having an india rubber body fastened to it to receive the rain1 which is measured off by a small graduated glass1 also contained in the box4 ,gentlemen travelling will find this compact observatory all that can be desired for meteorological observations4 #aef4 ,,implements4 ,the practical meteorologist will find the following articles very useful1 if not necessary4 ,they scarcely require description2 an enumeration will therefore suffice3--,weather ,diagrams1 or prepared printed and ruled forms1 whereon to exhibit graphically the readings of the various instruments to render their indications useful in foretelling weather1 c42--,meteorological ,registers1 or ,record ,books1 for recording all observations1 and the deductions2--,cloud ,pictures1 by which the clouds can be readily referred to their particular classification1 very necessary to the inexperienced and learners2--,cyclone ,glasses1 or ,horns1 outline ,maps with ,wind-markers1 are also useful1 especially in forecasting weather4 #aeg4 ,,hydrometer4 ,a simple kind of hydrometer is very much used at sea1 as a sea-water test2 and as the observations are usually recorded in a meteorological register or the ship's log-book1 it may not be altogether out of place to give a description of it here4 ,illustration3 ,fig4 #if4 ,illustration3 ,fig4 #ig4 ,it is constructed of glass4 ,if made of brass1 the corrosive action of salt-water soon renders the instrument erroneous in its indications4 ,the shapes usually given to the instruments are shown in figs4 #if and #ig4 ,a globular bulb is blown1 and partly filled with mercury or small shot1 to make the instrument float steadily in a vertical position4 ,from the neck of the bulb the glass is expanded into an oval or a cylindrical shape1 to give the instrument sufficient volume for flotation2 finally1 it is tapered off to a narrow upright stem which encloses an ivory scale1 and is closed at the top4 ,the divisions on the scale read downward1 so as to measure the length of the stem which stands above the surface of any liquid in which the hydrometer is floated4 ,the denser the fluid1 the higher will the instrument rise2 the rarer1 the lower it will sink4 ,the indications depend upon the hydrostatic principle1 that floating bodies displace a quantity of the fluid which sustains them equal to their own weight4 ,according1 therefore1 as the specific gravities of fluids differ from each other1 so will vary the quantities of the fluids displaced by the same body when floated successively in each4 ,the specific gravity of distilled water1 at the temperature of #fb deg4 ,f1 being taken as unity1 the depth to which the instrument sinks when gently immersed in such water is the zero of the scale4 ,the graduations extend from #j to #dj2 the latter being the mark which will be level with the surface when the instrument is placed in water1 the specific gravity of which is #a4jdj4 ,in recording observations1 the last two figures only--being the figures on the scale--are written down4 ,sea-water usually ranges from #a4jbj to #a4jcf4 ,a small tin1 copper1 or glass cylinder is useful for containing the water to be tested4 ,it should be wider than the hydrometer1 and always filled to the brim4 ,if fitted to a stand1 which is supported by gimbals1 it will be very convenient4 ,water in a bucket1 basin1 or other wide vessel1 acquires motion at sea1 and the eye cannot be brought low enough 7on account of the edges7 to read off the scale accurately4 ,errors of observation may occur with the hydrometer1 if it be put into water without being clean1 or without being carefully wiped4 ,the instrument is extremely accurate if correctly used4 ,it should be kept free from contact with the sides of the vessel2 and all dust1 smears1 or greasiness1 should be scrupulously avoided1 by carefully wiping it with a clean cloth before and after use4 ,whenever the temperature of the water tested differs from #fb deg41 a correction to the reading is necessary1 for the expansion or contraction of the glass1 as well as the water itself1 in order to reduce all observations to one generally adopted standard4 ,negretti and ,zambra's hydrometer1 with thermometer in the stem1 shows the density and temperature in one instrument4 ,for the following ,tables we are indebted to the kindness of ,admiral ,fitz,roy3-- ,,table for reducing observations made with a ,,brass ,,hydrometer1 assuming the linear expansion of brass to be #j4jjjjjieee for #a deg4 ,f4 ,the correction is additive for all temperatures above #fb deg41 and subtractive for temperatures below #fb deg4 ---------------------------------------- ------------------------------ t deg4,correction4t deg4,correction4t deg4,correction4t deg4,correction4 ---------------------------------------- -------------------- #cb -#j4jjad #dh -#j4jjaj #fd #j4jjjb #hj #j4jjbj #cc 4#jjad #di 4#jjji #fe 4#jjjc #ha 4#jjba #cd 4#jjad #ej 4#jjji #ff 4#jjjd #hb 4#jjbc #ce 4#jjad #ea -#j4jjjh #fg 4#jjje #hc 4#jjbd #cf 4#jjad #eb 4#jjjh #fh #j4jjjf #hd 4#jjbf #cg 4#jjad #ec 4#jjjg #fi 4#jjjg #he #j4jjbg #ch -#j4jjad #ed 4#jjjf #gj 4#jjjh #hf 4#jjbi #ci 4#jjac #ee 4#jjjf #ga 4#jjji #hg 4#jjcj #dj 4#jjac #ef -#j4jjje #gb 4#jjaj #hh 4#jjcb #da 4#jjac #eg 4#jjjd #gc 4#jjaa #hi 4#jjcc #db 4#jjac #eh 4#jjjc #gd #j4jjac #ij #j4jjce #dc 4#jjab #ei 4#jjjc #ge 4#jjad #ia 4#jjcf #dd -#j4jjab #fj 4#jjjb #gf 4#jjae #ib 4#jjch #de 4#jjaa #fa -#j4jjja #gg 4#jjaf #ic 4#jjdj #df 4#jjaa #fb #j4jjjj #gh 4#jjah #id 4#jjda #dg -#j4jjaj #fc #j4jjja #gi #j4jjai #ie #j4jjdc ---------------------------------------- ------------------------------ ,,table for reducing observations made with a ,,glass ,,hydrometer1 assuming the linear expansion of glass to be #j4jjjjjdfc for #a deg4 ,f4 ,the correction is additive for temperatures above #fb deg41 and subtractive for temperatures below #fb deg4 ---------------------------------------- ------------------------------ t deg4,correction4t deg4,correction4t deg4,correction4t deg4,correction4 ---------------------------------------- -------------------- #cb -#j4jjai #dh -#j4jjab #fd #j4jjjb #hj #j4jjbc #cc 4#jjai #di 4#jjaa #fe 4#jjjc #ha 4#jjbd #cd 4#jjah #ej 4#jjaa #ff 4#jjjd #hb 4#jjbf #ce 4#jjah #ea -#j4jjaj #fg 4#jjje #hc 4#jjbg #cf 4#jjah #eb 4#jjji #fh #j4jjjg #hd 4#jjbi #cg 4#jjag #ec 4#jjjh #fi 4#jjjh #he #j4jjca #ch -#j4jjag #ed 4#jjjh #gj 4#jjji #hf 4#jjcb #ci 4#jjag #ee 4#jjjg #ga 4#jjaj #hg 4#jjcd #dj 4#jjaf #ef -#j4jjjf #gb 4#jjab #hh 4#jjcf #da 4#jjaf #eg 4#jjje #gc 4#jjac #hi 4#jjcg #db 4#jjae #eh 4#jjjd #gd #j4jjad #ij #j4jjci #dc 4#jjae #ei 4#jjjc #ge 4#jjaf #ia 4#jjda #dd -#j4jjad #fj 4#jjjb #gf 4#jjag #ib 4#jjdb #de 4#jjad #fa -#j4jjja #gg 4#jjah #ic 4#jjdd #df 4#jjac #fb #j4jjjj #gh 4#jjbj #id 4#jjdf #dg -#j4jjac #fc #j4jjja #gi #j4jjba #ie #j4jjdh ---------------------------------------- ------------------------------ #aeh4 ,,newman',s ,,self-,,registering ,,tide-,,gauge4 ,at places where the phenomena of the tides are of much maritime importance1 a continuous series of observations upon the rise and fall1 and times of change1 is essentially necessary as a basis for the construction of good tide tables2 and as such observations should also be accompanied with the registration of atmospheric phenomena1 we have no hesitation in inserting a description of an accurate self-registering tide-gauge4 ,the tide-gauge1 as shown in the illustration1 consists of a cylinder1 ,a1 which is made to revolve on its axis once in twenty-four hours by the action of the clock1 ,b4 ,a chain1 to which is attached the float1 ,d1 passes over the wheel1 ,c1 and on the axis of this wheel1 ,c 7in about the middle of it7 is a small toothed wheel1 placed so as to be in contact with a larger toothed wheel carrying a cylinder1 ,e1 over which passes another smaller chain4 ,this chain1 passing along the upper surface of the cylinder1 ,a1 and round a second cylinder1 ,f1 at its further end1 is acted on by a spring so as to be kept in a constant state of tension4 ,in the middle of this chain a small tube is fixed for carrying a pencil1 which1 being gently pressed down by means of a small weight on the top of it1 performs the duty of marking on paper placed round the cylinder the progress of the rise or fall of the tide as the cylinder revolves1 and as it is drawn by the chain forward or backward by the rise or fall of the float4 ,the paper is prepared with lines equidistant from each other1 to correspond with the hours of the clock1 crossed by others showing the number of feet of rise and fall4 ,illustration ,the cylinder while in action revolves from left to right to a spectator facing the clock1 and the pencil is carried horizontally along the top of the cylinder2 and the large wheel being made to revolve by the rise and fall of the float1 turns the wheel with the small cylinder1 ,e1 attached to it4 ,if the tide is falling1 the small chain is wound round the cylinder1 ,e1 and the pencil is drawn towards the large wheel2 but if the tide is rising1 the small chain is wound on to the cylinder1 ,f1 by means of the spring contained in it1 which constantly keeps it in a state of tension4 ,thus1 by means of the rise and fall of the tide1 a lateral progress is given to the pencil1 while the cylinder is made to revolve on its axis by the clock1 so that a line is traced on the paper showing the exact state of the tide continuously1 without further attention than is necessary to change the paper once every day1 and to keep the pencil carefully pointed2 or a metallic pencil may be used1 which will require little1 if any1 attention4 ,a good self-registering tide-gauge is a valuable and important acquisition wherever tidal observations are required1 and the only perfectly efficient instrument of this kind is that invented by the late ,mr4 ,john ,newman1 of ,regent ,street1 ,london4 ,it is now in action in several parts of the world1 silently and faithfully performing its duty1 requiring no other kind of attention than that of a few minutes daily1 and thus admitting the employment of the person on any other service whose duty it would otherwise have been to have registered the tide4 ,it has done much by its faithful records in contributing to the construction of good tide tables for many places2 for those unavoidable defects dependent on merely watching the surface on a divided scale are set aside by it1 all erroneous conclusions excluded1 and a true delineation of ,nature's own making is preserved by it for the theorist4 ,,addenda4 #a4 ,french barometers are graduated to millimetres4 ,an ,english inch is equal to #be4ciied millimetres4 ,hence1 #cj inches on the ,english barometer scales correspond to #gfb millimetres on the ,french barometer scales4 ,conversions from one scale to another can be effected by the following formulae3-- 7#a7 ,inches millimetres divided by #be4ciied 7#b7 ,millimetres inches multiplied by #be4ciied ,of course1 a table of equivalent values should be drawn up and employed1 when a large number of observations are to be converted from one scale to the other4 #b4 ,in ,germany1 barometers are sometimes graduated with old ,french inches and lines1--the vernier generally indicating the tenth of a line4 ,,old ,,french ,,lineal ,,measure4 ,english ,inches4 #a douzieme1 or point #j4jjgd #ab points #a ligne #j4jhhh #ab lignes #a pouce #a4jfegfe #ab pouces #a pied #ab4ghib #a pied #cbd4g millimetres4 ,the ,germans indicate inches by putting two accents after the number2 lines1 by putting three accents2 #bg #c'''4he1 means #bg inches #c lines #he hundredths of a line2 more frequently1 they give the height in lines1 and the preceding number becomes #cbg'''4he4--,kaemtz4 #c4 ,rule for finding ,diameter of ,bore of a ,barometer ,tube4 ,if the maker has not taken care to measure the interior diameter directly1 it may be deduced from the exterior diameter4 ,the exterior diameter is first measured by calipers1 and1 by deducting from this diameter #j4a of an inch for tubes from 4#c to 4#e of an inch in external diameter1 we have an approximation to the interior diameter of the tube4--,kaemtz4 #d4 ,,wind ,,scales4 ,sea ,scale4 ,wind4 ,land ,scale4 ---------- ----- ----------- #j to #c ,light #j to #a #c #e ,moderate #a #b #e #g ,fresh #b #c #g #h ,strong #c #d #h #aj ,heavy #d #e #aj #ab ,violent #e #f ,pressure in ,velocity in ,pounds 7,land ,scale74 ,miles 7,avoirdupois7 7,hourly74 ------------- --------- ----------- #a_/b #a #aj #e #b #cb #aj #c #de #ba #d #fe #bf #e #gb #cb #f #hj #e4 ,letters to ,denote the ,state of the ,weather4 b denotes blue sky1 whether with clear or hazy atmosphere4 c cloudy1 that is detached opening clouds4 d drizzling rain4 f fog4 h hail4 l lightning4 m misty1 or hazy so as to interrupt the view4 o overcast1 gloomy1 dull4 p passing showers4 q squally4 r rain4 s snow4 t thunder4 u ugly1 threatening appearance of sky4 v unusual visibility of distant objects4 w wet1 that is dew4 ,a letter repeated denotes much1 as r r1 heavy rain2 f f1 dense fog2 and a figure attached denotes duration in hours1 as #ad r1 #ad hours rain4 ,by the combination of these letters1 all the ordinary phenomena of the weather may be recorded with certainty and brevity4 ,,examples4--b c1 blue sky with less proportion of cloud4 #b r r l l t1 heavy rain for two hours1 with much lightning1 and some thunder4 ,the above methods of recording the force of wind and state of weather were originally proposed by ,admiral ,sir ,francis ,beaufort4 ,they are now in general use at sea1 and by many observers on land4 #f4 ,table of ,expansion by ,heat from #cb deg4 to #bab deg4 ,f4 ,platinum #j4jjjhhdb of the length4 ,glass1 ,flint #j4jjjhaag with ,lead #j4jjjhfbb ,brass #j4jjahgjh ,mercury #j4jahjahj ,water #j4jdccbjj1 from #ci deg4 to #bab deg4 ,alcohol #j4aajj #cb deg4 to #agd deg4 ,nitric ,acid #j4aajj ,sulphuric ,acid #j4jfjj #g4 ,table of ,specific ,gravity of ,bodies at #cb deg4 ,f4 except water1 which is taken at #ci deg4#d4 ,water #a4jjj ,alcohol1 pure #j4gia proof #j4iaf ,mercury #ac4eif ,glass #c to #b4g ,brass #g4h to #h4ed ,platinum #ba to #bb4jj ,weight of a cubic foot of water1 at the temperature of comparison1 #fb4dbe lbs4 avoirdupois4 ,the pound avoirdupois contains #g1jjj grains4 ,air is #hac4fg times lighter than water4 ,the linear expansions are the mean values of the results of various experimentalists4 ,the specific gravities are as given in ,professor ,rankine's ,applied ,mechanics4 #h4 ,important ,temperatures4 ,under the circumstances of-- deg4 ,water boiling at #bab ,mercury boils at #ffj ,sulphuric ,acid #eij ,oil of ,turpentine #efj ,nitric ,acid #bdb ,alcohol #agd ,a ,saturated ,solution of ,salt #bah ,vital ,heat #if ,olive ,oil begins to solidify #cf ,fresh ,water freezes #cb ,sea ,water freezes #bh ,mercury freezes -#ci #i4 ,,table ,,of ,,meteorological ,,elements1 ,,forming ,,exponents ,,of ,,the ,,climate ,,of ,,london4 ---------------------------------------- ---------------------------- #ahda ,mean ,height of ,barometer1 reduced to #cb deg4 ,f41 at the mean to sea-level4 #ahfa4 ---------------------------------------- ---------- ,mean ,monthly ,range of ,barometer4 ,months4 ---------------------------------------- ----- ,mean of all the ,highest ,temperatures4 ---------------------------------------- ,mean of all the ,lowest ,temperatures4 ----------------------------------- ,mean ,temperature4 ------------------------------ ,mean ,temperature of ,dew-point4 ------------------------- ,mean ,degree of ,humidity4 ---------------------- ,mean ,number of ,rainy ,days4 ------------------ ,average ,rainfall4 ------------- ,average ,amount of ,cloud 7#aj overcast74 --------- ,prevalent ,winds4 ---------------------------------------- ----------------- ,inches4 ,in4 deg4 deg4 deg4 deg4 ,in4 ---------------------------------------- ----------------- ,january #bi4icba4dddc4bcc4gch4cce4dhi #aa #a4hg4g,w4 to ,n4 ,february #bi4ifba4bbdd4gcc4bch4dcd4dhe #aj #a4fg4d,s4 to ,w4 ,march #bi4ifga4bcej4jce4cda4gcf4dhb #aj #a4ef4f,n4 to ,e4 ,april #bi4ijga4jfef4hch4fdf4cci4igi #aa #a4hf4a,n4 to ,e4 ,may #bi4icaa4jbfd4ddd4beb4hde4egf #aa #b4af4a,s4 to ,w4 ,june #bi4ifjj4higa4bej4bei4bej4hgd #aa #a4if4a,w4 to ,n4 ,july #bi4igjj4gigc4hec4bfa4iec4igf #aa #b4gf4i,w4 to ,n4 ,august #bi4iedj4iggb4hec4dfa4ced4agg #aa #b4df4e,w4 to ,n4 ,september #bi4iigj4iefg4ddh4ief4iea4aha #ab #b4de4i,s4 to ,w4 ,october #bi4hfja4cceh4cdc4gej4bdf4jhg #ac #b4hf4i,s4 to ,w4 ,november #bi4ibia4ecdi4ccg4gdc4ddj4ahi #ab #b4dg4b ,s4,w4 ,december #bi4igia4ebde4jce4edj4acf4ihi #ab #a4ig4d ,w4 ---------------------------------------- ----------------- ,year #bi4idfa4afeh4jdb4cdi4bdc4ghbaccbe4cf4g -- ---------------------------------------- ----------------- #a #b #c #d #e #f #g #h #i #aj #aa ---------------------------------------- ----------------------------- ---------------------------------------- ------------- ,sun above the ,horizon on ,middle ,day4 ---------------------------------------- ----- ,,remarks4 ---------------------------------------- --------------------- ,hours4 ---------------------------------------- --------------------- ,january #h-a_/b,the majority of the nights are frosty4 ,february #aj #aj frosty nights on the average4 ,march #ab #ab ditto ditto ditto4 ,strong winds4 ,april #ad #f ditto ditto ditto4 ,may #ae-a_/b,very rarely frost4 ,june #af-a_/b,sun attains greatest ,north ,declination1 #bast4 ,july #af ,august #ad-a_/b ,september #ab-a_/b ,october #aj-a_/b;,a few frosty nights4 ,heavy gales4 ,november #i #aa nights frosty4 ,december #h ,sun attains greatest ,south ,declination1 #bast4 ---------------------------------------- --------------------- ,year -- ---------------------------------------- --------------------- #ab #ac ---------------------------------------- ----------------------- ,in the above ,table1 columns #a to #aj are results obtained at the ,royal ,observatory1 ,greenwich1 by ,j4 ,glaisher1 ,esq41 ,f4,r4,s4 ,the data contained in columns #b and #aj1 are deduced from observations extending over the years #ahda to #ahee inclusive1 and are copied from ,edward ,hughes' ,third ,reading ,book2 the other columns are results of observations made during the twenty years ending #ahfa4 ,the rest of the information is from ,luke ,howard's ,climate of ,london4 ,these valuable data indicate the characteristics of the weather in each month in the suburbs of ,london1 and will be found tolerably accurate as indications of weather1 and serviceable as standards for comparisons of observed results1 at most places in ,england4 ,,standard ,,works ,,on ,,meteorology ,,supplied ,,by ,,negretti ,,zambra4 ,,the ,,weather ,,book3 ,a ,,manual ,,of ,,practical ,,meteorology4 ,by ,vice-,admiral ,,fitzroy1 ,f4,r4,s41 ,m4,i4,f41 c4 ,price1 ,l#j #ae #f ,,the ,,law ,,of ,,storms1 ,by ,h4 ,w4 ,,dove1 ,f4,r4,s4 ,translated by ,r4 ,h4 ,,scott1 ,m4,a4 ,price1 ,l#j #aj #f ,l4 ,f4 ,,kaemtz',s ,,complete ,,course ,,of ,,meteorology1 ,translated by ,c4 ,v4 ,,walker1 ,esq4 ,price1 ,l#j #ab #f ,,practical ,,meteorology1 ,by ,,john ,,drew1 ,ph4,d41 ,f4,r4,a4,s4 ,price1 ,l#j #e #j ,,hygrometrical ,,tables1 ,adapted to the use of the ,wet and ,dry ,bulb ,thermometer1 ,by ,,james ,,glaisher1 ,esq41 ,f4,r4,s4 ,price1 ,l#j #b #f ,,tables ,,of ,,the ,,corrections ,,for ,,temperatures1 ,to reduce observations to the #cb deg4 ,fahrenheit1 for ,barometers with brass scales extending from the cistern to the top of the mercurial column1 ,by ,,james ,,glaisher1 ,esq41 ,f4,r4,s4 ,price1 ,l#j #a #j ,,table ,,of ,,the ,,diurnal ,,range ,,of ,,the ,,barometer1 ,by ,,james ,,glaisher1 ,esq41 ,f4,r4,s4 ,price1 ,l#j #j #f ,,tables ,,for ,,calculation ,,of ,,heights ,,from ,,observations ,,on ,,the ,,boiling-,,point ,,of ,,water1 ,adapted to the use of ,negretti and ,zambra's ,boiling-point ,apparatus4 ,price1 ,l#j #a #j ,a ,,thermometrical ,,table1 ,,on ,,the ,,scales ,,of ,,fahrenheit1 ,,reaumur1 ,,and ,,centigrade1 ,by ,,alfred ,s4 ,,taylor1 ,esq41 ,m4,d41 c4 ,price1 in ,sheet1 with explanatory ,pamphlet1 ,l#j #a #f ,,meteorological ,,tables1 ,for the reduction of ,barometrical and ,hygrometrical ,observations1 ,determination of ,heights by the ,barometer and ,boiling-point ,thermometer1 c4 ,by ,g4 ,,harvey ,,simmonds1 ,m4,b4,m4,s4 ,price1 ,l#j #b #f ,,barometer ,,manual1 ,compiled by ,vice-,admiral ,,fitzroy1 ,f4,r4,s41 ,for the ,board of ,trade4 ,price1 ,l#j #j #f ,,pocket ,,meteorological ,,register ,,and ,,note-,,book1 ,with ,diagrams for exhibiting the ,fluctuations of ,barometer1 c4 ,printed on metallic paper4 ,price1 with ,pencil1 ,l#j #c #j ,,london3 ,,printed ,,by ,,strahan ,,and ,,williams1 #g ,,lawrence ,,land1 ,,cheapside1 ,e4,c4 ,,negretti ,,zambra',s ,,patent ,,recording ,,and ,,deep-,,sea ,,thermometer4#bj ,this ,thermometer differs from all other ,registering or ,recording ,thermometers in the following important particulars3-- ,i4 ,the ,thermometer contains only ,mercury without any admixture of ,alcohol or other fluid4 ,,ii4 ,it has no indices or springs1 and its indications are by the column of ,mercury only4 ,,iii4 ,it can be carried in any position1 and cannot possibly be put out of order except by actual breakage of the instrument4 ,and lastly1 it will indicate and record the exact temperature at any hour of the day or night1 or the exact temperature at any depth of the sea1 irrespective of either warm or cold currents1 or stratum through which the ,thermometer may have to pass in its descent or ascent1 this last very special quality renders this ,thermometer superior for deep-sea temperatures to any others2 for those now being used in the ,challenger sounding expedition are liable to give erroneous indications owing to their indices slipping1 and otherwise getting deranged--7,this was proved by ,messrs4 ,negretti and ,zambra at a ,meeting of the ,british ,meteorological ,society17 and under certain conditions of temperature it is not possible by the old ,thermometers to obtain true temperatures at certain depths which might be required4 ,annexed is a copy of a report to the ,admiralty from ,captain ,g4 ,s4 ,nares1 of ,h4,m4,s4 ,challenger1 dated ,melbourne1 ,march #beth1 #ahgd1 which we have taken from ,,nature1 ,july #cjth1 #ahgd1 proving the assertion4 ,in the report to the ,admiralty of ,capt4 ,g4 ,s4 ,nares1 of ,h4,m4,s4 ,challenger dated ,melbourne1 ,march #be1 #ahgd1 ,capt4 ,nares1 speaking of the temperature of the ocean1 especially near the pack edge of the ice1 says3--',at a short distance from the pack1 the surface water rose to #cb deg41 but at a depth of #dj fathoms we always found the temperature to be #bi deg42 this continued to #cjj fathoms1 the depth in which most of the icebergs float1 after which there is a stratum of slightly warmer water of #cc deg4 or #cd deg4 ,as the thermometers had to pass through these two belts of water before reaching the bottom1 the indices registered those temperatures1 and it was impossible to obtain the exact temperature of the bottom whilst near the ice1 but the observations made in lower latitudes show that it is about #ca deg4 ,more exact results could not have been obtained even had ,mr4 ,siemens's apparatus been on board4' ,it seems to us that the difficulty mentioned is one which would certainly have been surmounted by ,messrs4 ,negretti and ,zambra's new ,recording ,thermometers1 a description of which appeared in ,,nature1 vol4 ix4 p4 #chg2 this being exactly one of the cases to which this instrument is peculiarly adapted4 ,we believe the inventors and makers have greatly improved their ,thermometer since our description appeared1 and no doubt means will be taken by the ,admiralty to transmit one to the ,challenger4 ,,description ,,of ,,the ,,deep-,,sea ,,recording ,,thermometer4 ,in the first place1 it must be observed that the bulb of the ,thermometer is protected so as to resist the pressure of the ocean1 which varies according to depth that of three thousand fathoms being something like three tons pressure on the square inch4 ,the manner of protecting the bulb was invented by ,messrs4 ,negretti and ,zambra in #aheg1 and has been latterly copied by other persons and brought out as a new invention4 ,the manner of protecting the bulb has been described by the late ,admiral ,r4 ,fitz,roy1 in the first number of ,meteorological ,papers1 page #ee1 published ,july #eth1 #aheg1 as follows3 ,referring to the erroneous readings of all thermometers1 consequent on their delicate bulbs being compressed by the great pressure of the ocean1 he says3--',with a view to obviate this failing1 ,messrs4 ,negretti and ,zambra undertook to make a case for the weak bulbs1 which should transmit temperature1 but resist pressure4 ,accordingly a tube of thick glass is sealed outside the delicate bulb1 between which and the casing is a space all round1 which is nearly filled with mercury4 ,the small space not so filled is a vacuum1 into which the mercury can be expanded1 or forced by heat or mechanical compression1 without doing injury to or even compressing the inner or much more delicate bulb4' ,illustration3 ,fig4 #a4 ,the construction of this instrument for deep-sea temperatures is as follows3-- ,in shape it is like a syphon with parallel legs1 all in one piece and having a continuous communication1 as in the annexed figure4 ,the scale of the ,thermometer is pivoted on a centre and being attached in a perpendicular position to a simple apparatus 7which will be presently described71 is lowered to any depth that may be desired4 ,in its descent the ,thermometer acts as an ordinary instrument1 the mercury rising or falling according to the temperature of the stratum through which it passes2 but so soon as the descent ceases1 and a reverse motion is given to the line1 so as to pull the ,thermometer towards the surface1 the instrument turns once on its centre1 first bulb uppermost1 and afterwards bulb downwards4 ,this causes the mercury1 which was in the left-hand column1 first to pass into the dilated syphon bend at the top1 and thence into the right-hand tube1 where it remains1 indicating on a graduated scale the exact temperature at the time it was turned over4 ,the woodcut1 ,fig4 #a1 shows the position of the mercury after the instrument has been thus turned on its centre4 ,a is the bulb2 ,b the outer coating or protecting cylinder2 ,c is the space of rarefied air1 which is reduced if the outer casing be compressed2 ,d is a small glass plug on the principle of ,negretti and ,zambra's ,patent ,maximum ,thermometer1 which cuts off1 in the moment of turning1 the mercury in the tube from that of the bulb1 thereby ensuring that none but the mercury in the tube can be transferred into the indicating column2 ,e is an enlargement made in the bend so as to enable the mercury to pass quickly from one tube to another in revolving2 and ,f is the indicating tube or ,thermometer proper4 ,in its action1 as soon as the ,thermometer is put in motion1 and immediately the tube has acquired a slightly oblique position1 the mercury breaks off at the point ,d1 runs into the curved and enlarged portion ,e1 and eventually falls into the tube ,f when this tube resumes its original perpendicular position4 ,the contrivance for turning the ,thermometer over may be described as a frame with a vertical propeller2 to this frame the instrument is pivoted4 ,on its descent through the water the propeller is lifted out of gear and revolves freely on its axis2 but so soon as the instrument is pulled towards the surface the propeller falls into gear and revolves in the contrary direction1 turning the ,thermometer over once1 and then becoming locked and immovable4 ,directions for adjusting the ,thermometer previous to its being lowered in the ,sea4 ,i4 ,the mercury must all be in the left-hand column4 ,,ii4 ,the short peg at the back of the thermometer must be in front of the stop plate ,s 2 in order to effect this1 pull the knob which stops the ,thermometer1 and slightly turn the propeller1 to make the ,thermometer advance sufficiently to escape the stop plate4 ,negretti ,zambra's ,patent ,atmospheric ,recording ,thermometer1 ,fig4 #c1 differs from the ,deep-sea ,thermometer by its not having the double or protected bulb1 it not being required for resisting pressures4 ,in this case the instrument is turned over by a simple clock movement1 which can be set to any hour it may be desirable2 the ,thermometer is fixed on the clock1 and when the hand arrives at the hour determined upon1 and to which the clock is set as in setting an alarum clock1 a spring is released and the ,thermometer turns over as before described4 ,illustration3 ,fig4 #b4 ,illustration3 ,fig4 #c4 ,messrs4 ,negretti and ,zambra have arranged a ,wet and ,dry ,bulb ,hygrometer upon the same plan4 ,,negretti ,,zambra',s ,,price ,,list ,,of ,,standard ,,meteorological ,,and ,,other ,,philosophical ,,instruments4 ,the marginal figures in this ,list and the numbers of the wood engravings refer to paragraphs in ,negretti ,zambra's ,treatise on ,meteorological ,instruments4 ,l s4 d4 #d ,standard ,barometers1 ,fortin's arrangement1 as ,fig4 #c with mahogany board #h #h #j ,ditto ditto with ,millemetre and ,english scales #i #i #j ,ditto ditto with tube1 #j4de internal diameter and millimetre scale #aj #aj #j ,observatory ,standard ,barometers1 extra large tubes and cisterns ,l#be #j #j #ce #j #j ,ditto ditto arranged for observations being taken by the ,cathetometer #ah #ah #j ,cathetometer1 for use with above #ba #j #j #i ,self ,compensating ,standard ,barometer1 ,fig4 #f #bj #j #j #aj ,standard ,barometer1 with electrical adjustment #ae #ae #j #aa ,pediment ,barometers1 ,fig #g ,l#a #a #j #b #b #j ,ditto ditto ,fig4 #h ,l#c #c #j #c #aj #j ,ditto ditto ,fig4 #i ,l#d #aj #j #e #aj #j ,ditto ditto ,fig4 #aj #h #aj #j ,ditto ditto ditto handsome carved mountings1 in mahogany1 oak1 or walnut wood ,l#h #h #j ,l#aj #aj #j #ab #ab #j #ad ,fitz,roy's ,storm or ,sea ,coast ,fishery ,barometer1 ,fig4 #ab #e #e #j ,ditto ditto with two verniers #f #f #j ,ditto ditto mounted in ornamental carved frames1 oak1 walnut1 or mahogany ,l#f #aj #j #h #h #j #ai ,marine ,barometers1 ordinary forms1 ,figs4 #ac and #ad ,l#b #bs4 ,l#b #ajs4 #c #c #j ,ditto ditto ,best mounted ,l#e #es4 #f #f #j #bj ,the ,board of ,trade or ,kew ,marine ,barometer1 ,fig4 #ae1 ,l#d #ds4 ,l#e #es4 #f #f #j #bb ,negretti and ,zambra's ,fitz,roy ,marine or ,gun ,barometer1 ,fig4 #af1 with ,n4 and ,z4's ,patent ,porcelain ,scales1 as used in ,her ,majesty's ,navy #e #aj #j ,extra ,tube for ditto #a #ae #j #be ,negretti and ,zambra's ,farmer's ,barometer or ,domestic ,weather ,glass1 ,fig4 #ag #b #aj #j #bh ,negretti and ,zambra's ,miner's ,barometers ,l#a #as4 ,l#b #bs4 #c #c #j #ca ,dial or ,wheel ,barometers1 ,figs4 #ah1 #ai1 #bj1 #ba ,l#c #cs4 ,l#d #ds4 #e #e #j ,ditto ditto in carved ornamental mountings ,l#e #ajs4 ,l#f #fs4 ,l#h #hs4 #aj #aj #j ,ditto ditto rosewood1 inlaid with pearl or metal4 ,made to order1 ,figs4 #bb and #bc4 ,price varying with size1 c4 #cg ,gay ,lussac's ,syphon ,tube ,mountain ,barometer ,l#f #f #j #h #h #j #cb ,standard ,syphon ,barometer1 ,gay ,lussac's arrangement1 ,fig4 #bd #e #e #j #ch ,negretti and ,zambra's ,standard ,mountain ,barometer1 with ,fortin's cistern1 with tripod stand and travelling case1 ,fig4 #cj #aj #aj #j #cd ,barograph1 or ,self-registering ,barometer1 with syphon mercurial tube4 ,negretti and ,zambra's improved arrangement1 ,fig4 #bf #ah #ah #j #be #j #j ,negretti and ,zambra's ,self-recording ,aneroid ,barometer1 with ,clock #bb #j #j #dh4 ,,aneroid ,,barometers4 ,aneroid ,barometers1 with card dials #d-a_/b inches diameter1 best quality4 #b #aj #j ,ditto ditto with silvered metal dial #c #j #j ,ditto ditto with ditto and thermometer #c #aj #j ,ditto ditto ditto with corrected scale1 as supplied by ,negretti and ,zambra to the ,royal ,navy #e #e #j ,aneroid ,barometers1 with elegantly-chased dials #d #d #j ,ditto ditto with raised ring on dial #e #e #j ,ditto ditto ditto with thermometer #f #f #j ,aneroid ,barometer1 for altitude measurements with revolving ring1 carrying index1 range of scale #bj1jjj feet #d-a_/b inches diameter1 with magnifier #h #h #j ,,pocket ,,aneroid ,,barometers4 ,fig4 #cd4 #di ,pocket ,aneroid ,barometer1 #b-c_/d inches diameter1 with silvered metal scale #c #c #j ,ditto ditto for measuring altitudes to #aj1jjj feet compensated for temperature1 in leather case #e #e #j ,ditto ditto ditto to #bj1jjj feet1 with magnifier #f #f #j #ej ,,watch-,,size ,,aneroid ,,barometers in gilt metal cases 7see figure #ce47 ,watch-,size ,aneroid ,barometer1 weather range ,l#c #c #j #d #d #j ,ditto ditto of best construction1 extra thin1 for meteorological observations or altitude measurements to #aj1jjj feet #e #e #j ,ditto ditto ditto to #bj1jjj feet1 compensated for temperature #f #f #j ,either of the above ,watch-size ,barometers may be had in ,stout ,silver ,cases at a cost of ,l#b #bs4 extra ,watch-size ,aneroid ,barometers in ,solid ,gold1 highly-finished cases4 ,l#ae #aes4 to ,l#ba4 ,table ,stands for ,aneroid ,barometers of ,carved ,oak or other woods1 #ajs4 #f;d41 #bes41 #ces41 to ,l#e #es4 ,ships' ,aneroid ,barometers1 in suitable mountings ,l#b #ajs4 ,l#c #cs4 ,l#e #es4 ,l#f #fs4 #dg ,sympiesometer1 for ,ship use ,l#c #c #j #d #aj #j ,ditto ditto ,pocket form1 ,fig4 #cb #d #d #j ,the ,sympiesometer is now rarely used1 the ,aneroid ,barometer being found equally sensitive and less liable to derangement4 #ef ,independent ,standard ,thermometers1 ,fig4 #cf #e #e #j #eg ,standard ,thermometers1 for ,boiling ,point ,apparatus #a #aj #j ,chemists' or ,brewers' ,standard ,reference ,thermometers ,l#a #as4 #b #b #j #dg ,chemical ,thermometers1 divided on the stem4 ,fig4 #dh4 #ajs4 #f;d4 #j #ae #j ,chemical ,thermometers1 ,boxwood ,scale #gs4 #f;d4 #ajs4 #f;d4 #j #ab #f #fd ,thermometers on ,boxwood ,scales1 ,fig4 #cg4 #as4 #as4 #f;d4 #bs4 #f;d4 #cs4 #f;d4 #j #d #f ,ditto ditto larger sizes #gs4 #f;d4 #j #ab #f ,ditto ditto ,engraved glass scales1 ,fig4 #ci #aes4 ,l#a #as4 ,l#a #es4 #a #aj #j ,,pocket ,,thermometers1 ,,in ,,various ,,mountings4 ,fig4 #ch #ajs4 #f;d4 ,fig4 #dj #ajs4 #f;d4 #aes4 ,fig4 #da #es4 #f;d4 #hs4 #f;d4 #abs4 #f;d4 #fc ,thermometers of extreme ,sensitiveness1 #aes4 ,l#a #ajs4 #b #b #j ,drawing ,room or ,mantel ,thermometers1 various mountings1 ,figs4 #db and #dc4 #abs4 #f;d4 #aes4 ,l#a #as4 ,l#a #ajs4 ,l#b #bs4 #b #aj #j ,bracket ,window ,thermometers1 ,fig4 #df #abs4 #f;d4 #aes4 ,l#a #as4 #a #aj #j ,bath ,thermometers1 ,figs4 #dd #gs4 #f;d4 #j #ae #j #ff ,sugar ,boiling ,thermometers ,l#a #abs4 ,l#b #bs4 #c #c #j #fg ,earth ,thermometers1 ,fig4 #ea ,l#a #ajs4 #b #b #j ,hot ,bed ,ditto #abs4 #f;d4 ,l#a #es4 #a #aj #j #fh ,marine ,thermometer1 ,fig4 #eb #gs4 #f;d4 #hs4 #f;d4 #j #aj #f #fe ,super ,heated or ,steam ,pressure ,thermometers1 ,fig4 #gd1 ,figs4 #di and #ej ,l#a #es4 ,l#a #ajs4 ,l#b #bs4 #b #aj #j ,,self-,,registering ,,thermometers ,,for ,,heat4 #gb ,negretti and ,zambra's ,patent ,standard ,maximum ,self-,registering ,thermometer1#ba ,fig4 #ed #a #a #j #gb ,negretti and ,zambra's ,patent ,maximum ,thermometer1 on boxwood scale #j #aj #f ,ditto1 ditto1 on ,negretti and ,zambra's ,patent ,solid ,porcelain or ,metal ,scales on oak mounting #j #ab #f #gj ,rutherford's ,maximum ,thermometer1 on boxwood or metal scale1 with steel index #es4 #f;d4 #gs4 #f;d4 #j #aj #f #ga ,phillip's ,maximum ,thermometer1 on boxwood or metal scale1 with air index #gs4 #f;d4 #aj #f #j #ab #f ,,self-,,registering ,,thermometers ,,for ,,cold4 #gc ,negretti and ,zambra's ,standard ,minimum ,self-,registering ,thermometer1 ,fig4 #ee #a #a #j #gc ,rutherford's ,minimum ,thermometer1 on boxwood or metal scale #cs4 #f;d4 #es4 #f;d4 #gs4 #f;d4 #j #aj #f #gc ,rutherford's ,minimum ,thermometer1 on ,negretti and ,zambra's ,patent solid porcelain scale #ajs4 #f;d4 #j #ab #f ,ditto1 on ,negretti and ,zambra's porcelain or metal scales and oak mounting #j #ab #f #gd ,negretti and ,zambra's ,horticultural ,self-,registering ,thermometer4 ,the scale is made of stout zinc1 enclosing the tube2 the figures and divisions are boldly marked for quickly and easily reading the indications1 ,fig4 #ef #j #c #f #hc ,negretti and ,zambra's ,patent ,solar ,radiation ,thermometer1 ,fig4 #fc #a #e #j #hd ,ditto1 ditto1 ditto1 in vacuo1 ,fig4 #fd #a #aj #j ,ditto1 ditto1 ditto1 improved form1 with test gauge #b #b #j #he ,negretti and ,zambra's ,terrestrial ,radiation ,thermometer #a #e #j ,brass ,stands for above1 ,fig4 #fe #j #e #j #gf and #gg ,negretti and ,zambra's ,patent ,mercurial ,minimum ,thermometers ,l#b #ajs4 #b #b #j #ha ,maxima and ,minima ,thermometers1 on ,sixe's arrangement1 ,fig4 #fb1 various forms of mounting #abs4 #f;d4 #ads4 #bas4 #cjs4 #b #b #j ,pocket ,maxima and ,minima ,thermometers1 ,negretti and ,zambra's ,patent1 in convenient cases ,l#b #bs4 #b #aj #j #hi ,deep ,sea ,registering ,thermometer1 with ,negretti and ,zambra's improved protected bulb1 in copper cylinder1 ,fig4 #fi4 #b #aj #j #hiba ,negretti and ,zambra's ,improved ,deep ,sea ,thermometer1 with vulcanite mountings1 in copper cylinder1 with door1 small size #b #e #j #ij ,negretti and ,zambra's ,patent ,recording ,deep ,sea ,thermometer #aj #aj #j #ia ,ditto1 ditto1 ditto ,recording ,thermometer #d #d #j #ib ,ditto1 ditto1 ditto ,hygrometer #f #f #j #ic ,improved ,boiling ,point ,mountain ,thermometer1 or ,hypsometric ,apparatus1 with ,tables1 ,figs4 #gb and #gc1 in leather case with strap #e #e #j ,extra ,thermometer for ,ditto #a #aj #j #ajf ,negretti and ,zambra's ,standard ,wet and ,dry ,bulb ,hygrometer1 ,fig4 #gi #b #b #j ,wet and ,dry ,bulb ,hygrometers1 various mountings #cjs4 #bes4 #bas4 #ads4 #j #aj #f ,pocket ,hygrometers1 in box ,l#b #bs4 #b #aj #j #ajc ,daniell's ,hygrometer1 ,fig4 #gg #c #c #j #ajd ,regnault's ,hygrometer1 ,fig4 #gh ,l#c #ajs4 #e #e #j ,aspirator for ,ditto ,l#a #aes4 #b #ae #j #aaj ,howard's ,rain ,gauge1 has a #e-;inch copper ,funnel1 with turned brass rim fitted to a stout stone-ware or glass bottle1 with a graduated glass measure1 divided to #ajjths of an inch #j #aj #f ,symons' ,portable ,rain ,gauge1 7#e-;inch7 with graduated glass measure1 japanned tin #j #aj #f ,ditto ditto in stout copper #j #ae #j #aaa ,glaisher's ,rain ,gauge1 the receiving surface is #h-;inches diameter1 of stout japanned metal1 with graduated glass measure1 ,fig4 #hd #a #a #j ,ditto ditto1 of stout copper #a #aj #j ,receiving ,pots for ditto1 extra #bs4 and #cs4 #f;d4 #aac ,rain ,gauge1 having a receiving surface of #ab inches diameter1 and graduated glass gauge tube1 divided to hundredths of an inch1 in japanned metal1 with brass tap #b #aj #j ,ditto ditto1 ,fig4 #he1 in copper #c #aj #j ,ditto ditto1 with sliding rod instead of graduated tube1 japanned tin #b #b #j ,rain ,gauges1 of any form or area made to order1 with suitable measuring glasses4 #abc ,lind's ,anemometer1 ,fig4 #hf #b #b #j #abe ,robinson's ,anemometer1 ,fig4 #hg #c #c #j ,ditto ditto1 ,improved arrangement ,l#d #ajs4 #e #ae #j ,ditto ditto1 with clutch movement1 ,fig4 #hh #f #ae #j ,negretti and ,zambra's ,improved ,air ,meter1 of extreme sensitiveness1 very portable #d #d #j ,large ,air ,meters made to order4 #abg ,osler's ,self-,registering ,anemometer and ,rain ,gauge1 ,fig4 #hi ,l#hd to #aej #j #j #abh ,berkley's ,anemometers fitted up to order1 to suit the ,observatory4 #aca ,gold ,leaf ,electrometer1 ,fig4 #ij #a #a #j #acc ,peltier's ,electrometer #d #d #j #acd ,bohnenberger's ,electroscope1 ,fig4 #ia #h #h #j #ace ,thompson's ,electrometer1 to order ,lightning ,conductors fitted up to order4 #adb ,ozone ,cage1 ,fig4 #ib #j #ah #j ,ditto ditto1 copper #a #e #j #adf ,leslie's ,differential ,thermometer1 ,fig4 #ic ,l#a #ajs4 #b #b #j #adh ,thermometer ,stand 7,glaisher's7 #c #c #j #adi ,thermometer ,screen for ,sea use #c #c #j #aej ,anemoscope1 or ,portable ,vane1 ,fig4 #id #b #e #j #aea ,evaporating ,dish1 ,fig4 #ie #a #b #f #aeg ,sea ,water ,hydrometers1 ,board of ,trade ,marine1 ,figs4 #if and #ig #j #e #f #aeh ,newman's ,self-,registering ,tide ,gauge1 ,fig4 #aeh1 fitted to the ,building to order ,from #ej #j #j ,further ,information as to ,price1 c41 will be found in ,,negretti ,,zambra',s ,,encyclopaedic ,,catalogue ,,of ,,mathematical1 ,,philosophical1 ,,optical1 ,,photographic1 ,,and ,,standard ,,meteorological ,,instruments1 ,containing very numerous ,comparative ,tables of ,reference1 and ,illustrated by upwards of ,,eleven ,,hundred ,,engravings4 ,royal #hvo4 ,cloth1 ,gilt ,lettered--,price #es4 #f;d4 ,,footnotes3 #a ,second ,number of ,meteorological ,papers1 issued by the ,board of ,trade4 #b ,with reference to these barometers1 we have received the subjoined testimonial1 with permission to use it as we please4 ,meteorologic ,office1 #abth ,june1 #ahfc4 ,,messrs4 ,,negretti ,,zambra1 ,the barometers which you have lately supplied to ,her ,majesty's ships through this ,office are much approved1 being good for general service1 afloat or on land4 7,signed7 ,r4 ,,fitzroy4 #c ,vide ,c4 ,daubeny1 ,f4,r4,s41 ,on ,climate4 #d ,vide ,report of the ,british ,association1 #ahfb4 #e ,see page #db for the ,tables4 #f ,the quotations in this section are from ,tyndall's ,heat considered as a ,mode of ,motion4 #g ,dr4 ,daubeny1 ,f4,r4,s41 ,on ,climate4 #h ,leslie ,on the ,relations of ,air1 ,heat1 and ,moisture4 #i ,tyndall's ,heat considered as a ,mode of ,motion4 #aj ,vide ,horological ,journal1 ,vol4 ,v4 #aa ,hygrometrical ,tables1 by ,j4 ,glaisher1 ,esq41 ,f4,r4,s4 #ab ,vide ,report of the ,british ,association1 #ahfb4 ,it may be added1 for the information of those who are about to commence observing1 that ,mr4 ,symons1 of ,camden ,road ,villas1 ,london1 is desirous of securing returns of rain-fall from as many stations as possible1 in order to render more complete his annual reports to the ,british ,association4 #ac ,luke ,howard's ,climate of ,london4 #ad ,vide ,third ,number of ,meteorological ,papers1 issued by the ,board of ,trade4 #ae ,elements of ,physics1 by ,c4 ,f4 ,peschel4 #af ,this description is modified from that in ,report of the ,jurors for ,class ,,xiii4 ,international ,exhibition1 #ahfb4 #ag ,all the ,year ,round1 ,no4 #bbd4 #ah ,all the ,year ,round1 ,no4 #bbd4 #ai ,vide ,jurors' ,reports4 #bj ,see also page #ij of this ,treatise4 #ba ,these ,instruments are the only ,maximum ,thermometers that can be recommended1 as unless they be broken1 they cannot be put out of adjustment4 ,fully described under the head of ,standard ,maximum ,thermometers in our large ,catalogue1 and page #gb of our ,treatise on ,meteorological ,instruments4