458 Mr. R. A. Houstoun : 
The bright yellow line of Hg 
2790 was also investigated, and was Fig. 6. 
found as in fig. 6, B being so close Cp yO 
to C as sometimes not to be dis- 
tinguished from it. Calculating A e FE 
the distance dd from an imaginary | | oe 
line between C and D from obser- 
vations made at three different times, we get 
AN ee: —°203 —*133 —°180 
Big trans — 072 — 081 
C ertaler, — 032 —°031 — 035 
DE EY x, +032 +°035 + 039 
Wiad ieky +°139 +°139 +157 
On one occasion while we measured the differences, the 
frequency of the hammer changed and the line A was seen to 
move further out. This was seen only once. The satellite 
systems are of course exactly the same when viewed across 
and along the direction of discharge ; and no component is 
ever plane-polarized. 
§ 2. These two lines were also examined in the electric 
arc, the soft core of the lower carbon being bored out, a 
rubber tube being fastened to its ]ower end and connected to 
a mercury reservoir, by 
raising and lowering which 
the supply of Hg vapour in 
the are could be altered, 
when some extraordinary 
cases of reversal were ob- 
served. These remained 
steady for long. Figs.7 & 
8 represent what the green 
line reversed into. Here the 
light maxima were rather bands than lines. dA’ is given as 
if the lines were satellites, for which 
Fig.7. 


yy, A 8. clam 
they were at first taken. Fig. 8, 
Yi iG A c 
—0°195 —0153 —0°095 0:065 
x, X, Rete | 
07140 0°167 Gio Hee 
The numbers represent distances from B. 
Similar measurements for fig. 8, taken from a point mid- 
way between L and M, are | 
G H L M N 
—0'246 —0:150 —0'032 40:022 (a2t 
