J. W. Draper—Distribution of Heat in the Spectrum. 178 
face of the pile is white, and the multiplier gives the whole 
heat of the visible spectrum. By subtracting the foregoing 
measure from this, we have the heat of the less refrangible 
region, that is from a to the centre of the spectrum. 
As a matter of curiosity, the experimenter may now, if he 
pleases, remove the screens A,7; the light on the face of the pule 
will still be white, and the multiplier will give the force of the 
entire radiations, except so far as they are disturbed by the 
thermochrose of the media. These measures, as not bearing 
upon the problem under consideration, I do not give in the 
following tables. : 
Tnstead of advancing the screen 7 from the less toward the 
“nt refrangible regions, I have very frequently moved h 
om 
mode of experimentation, as I did not find that its results dif- 
fered in any important degree from those obtained as just 
described. 
The variation in different experiments may generally be 
traced to errors in placing the screen ¢ with exactness on the 
centre of the spectrum and on the line A. ; 
or the sake of more convenient comparison, I have reduced 
all the different sets of experiments to the standard of 100 for 
the whole visible spectrum. 
ov wave made use of four prisms: (1) rock salt ; (2) flint glass ; 
(3) bisulphide of carbon ; (4) quartz, cut out of the crystal so 
give a single image. 
All the observations here recorded were made on days when 
there was a cloud 
Taste I,—Distribution of heat by rock-salt. 
ries I. Series IT. 
Heat of the whole Moet cite Maes sak on ee 
@) see guste. ge 
In this table the column marked Series L. gives the mean of 
four sets of measures, and that marked II. of three, At the 
ning of each set the rock-salt was repolished. 
Taste IL— Distribution of heat by flint-glass. 
Series I. Series IT. 
(1) Heat of the whole visible spe trum,. .------- 100 —s-: 100 
(2) . more refrangible region, -------- 49 
(3) vy less « Rie 
ig I. gives the mean of ten sets of measures, Series IL. of 
eg i : 
52 
51 48 
