of Magnetical and Meteorological Instruments. 327 
ronto is 20’ to an inch, the light being thrown in such a Way as 
to divide the space unequally, and allow the greatest range to the 
east, the direction in which the principal movements occur. 
The lamp is supported by a tripod stand about three feet high, 
with an elevating lever for raising the. top, 3. 
which consists of three distinct parts; the 
lowest of these (a) turns in azimuth round 
a pivot, the second ( b) slides by a slow mo- 
tion screw, in a groove, on the face of the 
first, the third (c) slides in like manner on 
the second, but transversely: by these ar- 
Tangements, first, the luminous slit can be 
uare to a tripod s 
Similar to that of the lamp, the feet of which should rest on a 
solid support. 
imi i isturbances in 
limit allowed for that element. It is to be expected that many more distur’ 
proportion will be recorded by the ee ic process than were pte not 
of the more extreme degrees, or such as to alter materially the above scale of relative 
fir 
"© The position of the stand for the lamp pe Be such that the cone of rays re- 
i ite clear the chimney, w 
flected from the mirror shall not qui imum is cut off by a screen slipped a little 
centre of the cylinder, the chimney should 
imilar segment on 
