ee, ee ee Se SN ee 
Hinrichs on Dark Lines in the Spectra of the Elements. 31 
of our atmosphere to the rays of heat and the chemical rays as 
well as to those of light. * The importance of this matter in cer- 
tain astronomical studies is not to be underrated; since we often 
notice the tendency to an erroneous estimate of the relative bril- 
liaucy of a comet’s nucleus and its tail as seen through the even- 
ing twilight in the most interesting part of its orbit; also in 
investigations upon the form of our Milky Way based upon the 
number of stars visible to Herschel in his guages, or observed 
by Bessel and Argelander in their zones. 
or the present we shall merely append a table of the com- 
puted values of E for the two values of E, given in (B) and (C), 
together with the corresponding values abstracted from the table 
given by Bouguer, p. 382. The 2d, 8d, and 4th columns give 
the E which results from assuming 7,=1. The 5th column 
contains the quotient zc for the value (C) of E,. 
oO 
j Bouguer’s Clark’s rk’s 
0 gee oe : observations. observations- deni 
0° 0°8123 08149 0°8017 1:0000 
10 0 8098 08123 0-7990 0°9966 
20 08016 042 0°7904 09859 
30 07866 0-7894 0°7746 0°9664 
40 07624 07654 0°7494 0:9347 
50 07237 07272 07091 0 8844 
60 06613 0°6639 0 8 08017 
70 05474 0°5496 075241 06537 
80 03149 0-3076 02801 03494 
90 00006 0-0000 0-0000 
Art. IV.—On the Distribution of the Dark Lines in the Spectra 
of the Elements; by Prof. Gustavus Huyricus, lowa State 
University.. 
As soon as I heard of the great discovery of Kirchhoff and 
Bunsen, I ore sure that the dark lines of the elements would 
ve to be distributed according to simple laws, and that these 
ne might lead us to a knowledge o relative dimensions 
the atoms. But it was only quite recently that I was enabled to 
study the distribution of these lines in its detail, Prof. Silliman 
Jr. having kindly sent me Kirchhoff’s two memoirs. Yet I 
limited my in er to the group of the alkaline earths and 
iron; for whatsoe ver s true fe some lem ents will also oun 
applicable to the ficultides ‘of them; and besides Kirchhoff’s 
easurements are not at all to be considered as final, neither does 
te give all lines that may be observed: so that the material at 
hand ean justify only a preliminary GiveatSpation, to be pel 
and modified by more complete and more accurate observa’ 
