6 
PROFESSOR TYNDALL ON THE DIAMAGNETIC FORCE, ETC. 
diamagnetic bodies is precisely the same as that of magnetic ones. In this unsettled 
state of the question nothing remained for me but a complete examination of the 
nature of the diamagnetic force, and a thorough comparison of its phenomena with 
those of ordinary magnetism. This has been attempted in the following pages, with 
what success it must be left to the reader to decide. 
Before entering upon the principal inquiry, I will introduce one or two points 
which arose incidentally from the investigation, and which appear to be worth 
recording. 
I. ON THE MAGNETIC PROPERTIES OF WOOD. 
No experiments have yet been made, to determine the influence of structure upon 
the magnetic deportment of this substance ; and even on the question whether it is 
magnetic, like iron, or diamagnetic, like bismuth, differences of opinion appear to 
prevail. Such differences are to be referred to the extreme feebleness of the force 
proper to the wood itself, and its consequent liability to be masked by extraneous 
impurity. In handling the substance intended for experiment the fingers must be 
kept perfectly clean, and frequent washing is absolutely necessary. After reducing 
the substance to a regular shape, so as to annul the influence of exterior form, its 
outer surface must be carefully removed by glass, and the body afterwards suspended 
by a very fine fibre between the poles of a strong electro-magnet. 
The first step in the present inquiry was to ascertain whether the substance 
examined was paramagnetic* or diamagnetic. It is well known, that, in experiments 
of this kind, moveable masses of soft iron are placed upon the ends of the electro- 
magnet, the distance between the masses being varied to suit the experiment. In 
front of a pointed mass of iron of this kind, a cube of wood was suspended, and if, on 
exciting the magnet, the cube was repelled by the point, it was regarded as diamag- 
netic ; if attracted, it was considered to be paramagnetic. 
The force was considerably intensified by placing the two Fig’ l- 
moveable poles as in fig. 1, and suspending the cube at a 
on the same level with the points ; a diamagnetic body 
placed there is, on the development of the magnetic force, 
forcibly driven from the line which unites the points, while 
a magnetic body is forcibly drawn in between them. 
Having thus observed the deportment of the mass, the cube was next suspended 
between the flat ends of the poles sketched in fig, 1. The parallel faces were about 
three-quarters of an inch apart, and in each case the fibre of the suspended wood was 
horizontal. The specimen first examined was Beef-wood : suspended in the position a, 
fig, 1, the mass was repelled : suspended between the flat poles, on exciting the mag- 
* The effects exhibited by iron and by bismuth come properly under the general designation of magnetic 
phenomena : to render their subdivision more distinct Mr. Faraday has recently introduced the 'wordi paramag- 
netic to denote the old magnetic effects, of which the action of iron is an example. Wherever the word mag- 
netic occurs, without the prefix, it is always the old action that is referred to. 
