PHILOSOPHICAL TRANSACTIONS. 
I. The Bakerian Lecture. — On the nature of the Force hy which Bodies are repelled 
from the Poles of a Magnet ; to which is prefixed, an Account of some Experi- 
ments on Molecular Influences. By John Tyndall, Ph.D., F.R.S., Membre de la 
Socidt^ Hollandaise des Sciences ; Foreign Member of the Physical Society of 
Berlin, and Professor of Natural Philosophy in the Royal Institution. 
Received October 31, 1854, — Read January 25, 1855. 
Contents : — 
Introduction. 
1. On the Magnetic Properties of Wood. 
II. On the Rotation of Bodies between Pointed Magnetic Poles. 
III. On the Distribution of Force between Flat Poles. 
IV. Comparative View of Paramagnetic and Diamagnetic Phenomena : — 
1. State of Diamagnetic Bodies under Magnetic Influence. 
2. Duality of Diamagnetic Excitement. 
3. Separate and joint action of a Magnet and a Voltaic Current on Paramagnetic and Diamagnetic 
Bodies. 
V. Further Comparison of Paramagnetic and Diamagnetic Phenomena: — Diamagnetic Polarity. 
VI. Concluding Observations on M. Webee’s Theory of Diamagnetism, and on AMpiiRE’s Theory of Molecular 
Currents. 
INTRODUCTION. 
From the published account of his researches it is to be inferred, that the same 
heavy glass, by means of which he produced the rotation of the plane of polarization 
of a luminous ray, also led Mr. Faraday to the discovery of the diamagnetic force. 
A square prism of the glass, 2 inches long and 0'5 of an inch thick, was suspended 
with its length horizontal between the two poles of a powerful electro-magnet ; on 
developing the magnetism the prism moved round its axis of suspension, and finally 
set its length at right angles to a straight line drawn from the centre of one pole to 
that of the other. A prism of ordinary magnetic matter, similarly suspended, would, 
as is well known, set its longest dimension from pole to pole. To distinguish the two 
positions here referred to, Mr. Faraday introduced two new terms, which have since 
come into general use; he called the direction parallel to the line joining the poles, 
the axial direction, and that perpendicular to the said line, the equatorial direction. 
mdccclv. 
B 
