570 
SECOND REPORT - 1832 , 
Mr. Barlow, he stated, has employed a globe of wood, co¬ 
vered with coils of wire, to illustrate terrestrial magnetism on 
electro-magnetic principles : he exhibited an iron sphere, fitted 
up for the same purpose, which shows a more powerful polarity; 
it is an 8-inch shell, surrounded between the tropics with 4 coils 
of wire, and turning on an horizontal axis at right angles to its 
polar axis. 
His concluding observations related to the distribution of 
magnetic polarity in copper and other non-ferruginous metal¬ 
lic plates. After the discovery, by M. Arago, of the magneti- 
cal effects produced by the rotation of such plates, Mr. Stur¬ 
geon had diversified the experiment by giving the discs a vibra¬ 
tory in place of a rotatory motion, and had thus succeeded in 
developing phenomena which he considered distinct from those 
first shown by the experiments of Arago : he had observed the 
deflections of a magnetic needle, produced by the force excited 
in the discs when rotated between the poles of a horse-shoe 
magnet, and had investigated the distribution of that force. 
5. CHEMISTRY. 
Abstract of Observations on Atmospheric Air. By William 
Prout, M.D. 
[When this paper was read, different tables, containing the 
details of the observations, were exhibited, but which were not 
intended for publication as yet.] 
The observations in the present communication are chiefly con¬ 
fined to two points,—the absolute weight of atmospheric air ; 
and the law of its expansion by heat. 
1. Of the weight of dry atmospheric air at 32°. In deter¬ 
mining the absolute weight of a gaseous body, there are three 
things to be especially considered and settled in the first place ; 
viz. the barometer, the thermometer, and the weights and mea¬ 
sures to be employed. 
The barometer employed in the whole of the present experi¬ 
ments was made expressly for the purpose, with the greatest, 
care. The internal diameter of the tube is *575 inch, and it is 
guarded at bottom bv platina, in the manner recommended by 
Mr. Daniell. The distance between the upper and lower sur¬ 
faces of the mercury is determined by a brass rod, ending at 
