418 Scientific Intelligence. 
The third lower octave with a wave length 0:0024 falls outside of the 
limit of least refrangibility. 
In all therefore the solar spectrum embraces somewhat more than two 
and a half odtaves 
so small that he was obliged to abandon the hope of obtaining reliable 
results in this manner. He however deduces the curve of distribution of 
the heat in the diffraction spectrum from that of the refraction spectrum. 
From this curve, it appears that in the diffraction spectrum the dark rays 
of heat occupy a space which is about three and a half times as broad as 
the whole visible spectrum. 
n a second memoir, the author returns to the subject of the sag 
ment of his experiments with Cauchy’s formula for dispersion above 
c ! . 
ne = i2 (1.) 
neglecting the higher powers of 3 
If we substitute in this equation the values 4= 0000396 for the line 
H, and n= 1°546 for crown-glass, we have 
0-41839 = a-+-c.6376900. (2.) 
If we substitute the value 4—=0-00069 for the line B and n= 1°546 we 
have 
0°42943 —a-+c.2100400. (3.) 
By combining these two equations we find 
a= 0°43436 
¢ == —0:0000000028477, 
and substituting these values in equation (1.) we have 
0000000002347 (4.) 
i2 
rVuTtVV 
of refraction for crown-glass, and 2 the corresponding wave 
=o we have 
ue . the index 
This is Cauchy’s formula for the special case that ie in the 
1 
--5 = 043436 or n= 1°516, 
n 
and this is the least value of the index of refraction re is ay 
. ’ i . In. : 
ing to Cauchy s formula, Hence it appears that ee 1-526, 2a 
wave length diminishes from 0-000396™™ to 0-00069""™ ; when agar 
the index diminishes from 1-526 to 1°517 the corresponding vend, a 
t, according to the formula, to increase from 0°00069 to mAnIys © 
