curving sicleB of * round dieMeo. In order to axrose more - - 

 than one dish **=***& behind each screen B o that none would be 



shaded by* another, a rack was made to fit inside the box with ^ 



cleats projecting inward from the, ends so that three dishes c/culd - 



he elipped into it one above the other.The light .entering through 

 the screen at the end of the box , fell equally on the one exposed 

 sid e of each of the three dishes. The rack containing the dishes 

 could be easily lifted out and carried to the microscope for exam^C 

 ati on without dicing the ,^^ ^^^-^^ 



The spectrosccpic analysis of the light passing the screens 

 determine, definitely the quality of light entering each box. It is 

 at once evident that the quantity or intensity of light behind 

 filte **. plac ed at #*W* equal distances from the source, ^ 

 vari3 3 ,both because the intensity of light transmitted by the differ* 

 ent screens is dif^erent,and because the different colors are not 

 radiated by the arc with equal intensity .This being the case , dif- 

 erences inrf results obtained behind the screens .could not be attri- 

 buted to differences in the ^^^^^^^^^ __ 

 energy of *& colored lights ift^the thermopile and sensitive gal 



vSnometer., The thermopile is very sensitive to tne energy of 



/\ 



any ether vibtations whether they be the longer infra-red or so- 

 called heat rays, or the shorter, actinic rays^of the spectrum. 



The method worked out for ^eliminating the intensity variable 

 in the use of the filters employed for thtsr investigations, consisted 

 in finding the distance * from the light source at which each box 

 with its colored window should be placed in order that the intensity^ 



as indicated by the deflection of the galvanometer when tho opeft- 



the filter 

 Qnd O f- the thermopile was exposed to the light behind & , was 



in each case. 



It seems necessary, on account of the questions which have 

 been raisedjduring .he course of this work, to stsfe here that the 

 thermopile is equally sensitive to the energy of r the red and^he vio- 

 let ens of .he spectrum, and is, therefore, an accurate measure 



