72 MR. BROOKE ON THE AUTOMATIC REGISTRATION OF MAGNETOMETERS, 
The six meteorological instruments of which a continuous registration is proposal 
to be obtained by the means above described, are the declination magnet, the hori- 
zontal and vertical force magnetometers, the barometer, the thermometer, and the 
psych rometer ; and by the arrangements above described, two of these may be regis- 
tered on the opposite sides of each of three cylinders ; the declination and horizontal 
force magnetometers on a cylinder placed horizontally, as represented in the Plate. 
In this case the describing a base-line would be most readily effected by a third lamp ; 
The horizontal force magnetometer and the barometer on a vertical cylinder, the long 
arm of the barometer index being placed horizontally ; and the thermometer and 
psychrometer on a second vertical cylinder, which must necessarily be placed in the 
open air. This arrangement will not however be attended with any difficulty, if the 
lamps are inclosed in a case similar to a magic lanthorn, the chimney of which is 
protected from the influence of descending currents, either by a revolving cap with a 
spiral lamina attached to it, or by Faraday’s ingenious expedient of interrupting the 
continuity of the chimney at two or more points, by parallel conical surfaces. The 
apparatus for carrying the vertical cylinders is represented in Plate VI. figs. 4 to 8. 
Figs. 9 and 10, Plate VI., are views of a carrier for the bifilar magnetometer. The 
stem to which the mirror is attached has a stirrup to hold the bar at the lower, and a 
torsion circle at the upper end. To the index-plate which moves with stiff friction 
on the torsion circle is attached a right- and left-handed screw, carrying two pulleys 
under which the suspension skein passes. These may be adjusted by the screw to 
give the requisite degree of sensibility to the magnet. A more accurate adjustment 
of the angle of torsion may, if requisite, be obtained by a tangent screw attached to 
the index, and gearing with the circumference of the torsion circle. 
Keppel Street , 
November 23rd, 1846. 
Postscript . — In the endeavour to avoid prolixity, the author may perhaps have 
omitted some details which would have facilitated the construction of the apparatus. 
On some few points, on which circumstances have appeared to render further infor- 
mation necessary, that has been embodied in the description of the Plates : he will, 
however, be at all times ready to further the objects of science, by communicating 
any required details to those who may be disposed to make a practical application 
of them. 
The author takes this opportunity of publicly and gratefully expressing his thanks 
to the Council of the Royal Society for their liberal contribution towards defraying 
the expenses of the apparatus . — May 24, 1847. 
