ea oe 
ate por tie Saag h § 
Chemistry and Physics. 417 
he case of crown-glass, a space which is almost as long as the entire 
visible spectrum, and this result corresponds nearly with those of Franz, 
lh the spectrum obtained by means of a pristn of rock salt, the thermic 
maximum lies still farther outside of the red, than in the case of the 
measurements of Melloni above mentioned. e dark thermic pro- 
n of the spectrum is, according to these experiments not greater 
for rock salt than for glass. 
ftefraction of the extreme dark rays of heat in the solar spectrum, is 
about 1-506 
The results of the author’s experiments, as we shall see farther on, do © 
tot agree with Cauchy’s formula for dispersion, which is intended to ex- 
i the relation between the wave length and the index of refraction. 
relation the author endeavors to express by an empirical formula 
of the form 
Gus w==a-+be+ce? Si on BAS 
ji thich w represents the wave length, e the index of refraction, ed a, 
oe © constants determined by experiment. This formula gives for » 
ve length of the extreme rays of heat in the solar spectrum and for 
“index of refraction of 1-506, the value 
ce w—0-00177™™. , 
vi same result very nearly is obtained by 4 graphical construction, 
gives ; 
w—0-0019™™. 
The author takes the mean of these two determinations, namely, 
AR sien w = 000182", 
Wave length ark rays. gs 
The wave farts of canal seisdeivest rays in the sun’s light is, 
3 
’s jine D in the 
wave length 0-0006, corresponding to decors 
The is the next lower octave of these most sefrangin ay the middle 
of the second lower octave with a wave Jength 0°0012 me 
dark rays of heat of the solar spectrum. 
SEtoND SERIES, Vou. XXVII, No. S1.—MAY, 1859. 
54 
