J. W. Draper—Distribution of Heat in the Spectrum. 163 
Herschel’s method. Leslie used a differential with small bulbs. 
Melloni, Miiller, Tyndall, a thermo-electric pile, the form pre- 
ferred being the linear. This was advanced successively 
ne all the radiations, and the deflections of the multiplier 
oted. 
Is not this method | defective? Does it not neces- 
sarily lead to incorrect results 
There is an inherent defect in the prismatic spectrum—a 
points insisted on is the a of using wave-lengths in the 
ent and discussion o 
Which T believe I was the first to make, and which I renew 
of the prismatic or dispersi haps b t 
: ; persion spectrum, may perhaps be Mos 
<a sfactorily recognized on examining such as trum by the 
we gama or interference one. By the aid of fig. ct 
one. . : 
= may be done 2 J > X 
ay f | Fie 1. NS wy Pe 
aA pop E F ae H 
ee seat 
| | | 
rE Diffraction Spectrum 
| foie bapa t 
| | 
ee ee ee 
Regarding the space between the fixed lines D and E as rep- 
i 
Tesenting the central region, in each the fixed lines D and E are 
ca coincident. Che cttw lines are laid off —— pacsecas 
€y appear through the flint-glass prism of the spectro- 
Scope; those of the diffraction are arranged according to their 
