560 
SECOND REPORT - 1832 . 
Experiments with the flat needle. 
March 27, 1832 ;—300 vibrations in 1054*95 
April 2,-1052*50 
- 19,- 1051-69 
CornbrooJc , Manchester. 
Cylindrical needle, No. 1. 
April 18, 1832;—300 vibrations in 798*78 
Flat needle. 
April 18, 1832;—300 vibrations in 1051*71 
On the Method of employing vibrating Magnets in the Investi¬ 
gation of the Magnetic Intensity of the Earth. By William 
Snow Harris, F.R.S. &c. 
The many irregularities to which the magnetic pendulum is 
subject, have rendered the method of investigating terrestrial 
magnetism by the oscillations of a freely suspended magnet, 
though perfect in theory, liable to much uncertainty in prac¬ 
tice. In this paper, the author has entered upon some of the 
most important of the causes of these irregularities, and has 
endeavoured to apply practically some general principles, in 
experimenting with vibrating magnets, by means of which more 
perfect results may be arrived at. 
The leading points treated of in this paper are as follow: 
1. The advantages of observing the oscillations of the mag¬ 
netic pendulum in a rare medium, with a description of a 
recently constructed apparatus for that purpose. 
2. The means of detecting changes in the force of magnetic 
bars. 
3. The influence of temperature on the state of vibration of 
a bar, either in altering its magnetic conditions, or changing its 
angular inertia. 
4. The possibility of rendering the magnetic state of bars 
invariable for certain temperatures. 
5. The influence of some mechanical conditions incident to 
the mode of suspension of a bar on its rate of vibration. 
6. The influence of the sun’s rays, of artificial light, and of 
free electricity pervading a vacuum, on the state of oscillation. 
The author observes, that although the mere presence of a 
resisting medium is not prejudicial to the rate of vibration, 
supposing every attendant circumstance to remain the same; 
yet from a variety of changes to which such a medium is liable, 
