[ 456 ] 
LVI. Some Spectroscopic Notes. By Rosurr A. Houstotn, 
M.A., B.Sc., Research Student in the University of Glasgow*. 
§ 1. [ a communication made to the Royal Society (“ On 
the Radiation of Heliumand Mercury in a Magnetic 
Field,” by Prof. A. Gray, F.R.S., and Walter Stewart, 
D.Se., with Robert A. Houstoun and D. B. Macquistan, 
Proc. Roy. Soc. vol. Ixxii. No. 477) certain measurements 
were given of the wave-lengths of the satellites of the green 
line in Hg. ‘These measurements disagree with those of 
Fabry and Perot; they have since been verified, and there 
seems evidence to show that the satellite system of the green 
line varies considerably under different conditions. 
According to Michelson (Phil. Mag. 
(5) xxxiv. p. 280, 1882) the green line Fig. 1. 
of Hg is fourfold. It consists of a 
narrow bright line in the middle of a +100 
broader weaker one. Then follow three 
weaker lines towards the red (fig. 1), the 
values of dd being about +0-075, 
+0°100, and +0°125 Angstrom units. 0 a 
Fabry and Perot (C. R. 1898, p. 409) Fig. 2. 
represent the line as having two attend- if 
ant lines +°008 and +°092 (fig. 2). 
Later they make it fivefold (C. R. | | 
1899, exxvill. p. 1156), one very weak oo Ree 
component on the violet side, —0-044, 
and three on the red side,.0-009, 0°082, ‘008 
and 0°136 (fig. 3). 
Finally, they make it sevenfold (P. Zeeman, Astroph. 
Fig. 3. 
044 082 («0.156 
+.009 
Fig. 4. 


{as 1 
—.224 “3082 
—.076 008 -082 0-136 
Journal, xv. p. 218), the differences being —0°224, —0:076, 
—0°052, 0°008, 0°082, and 0°136 (fig. 4). 
* Communicated by Prof. A. Gray, F.R.S. 
