ON THE POLARITY OF THE DIAMAGNETIC FORCE. 
241 
fibres which support an astatic arrangement of two magnets, the front one of which, 
SN, is shown in the figure. An enlarged section of the instrument through the 
system of magnets is shown in fig. 4. The magnets are connected by a brass cross- 
piece, in which is the point of suspension P ; and the position of the helices is shown 
Fig. 1. 
Fig. 2. 
Fig. 3. 
to be between the magnets. It will be seen that the astatic system is a horizontal one, 
and not vertical, as in the ordinary galvanometer. The black circle in front of the 
magnet SN, fig. 2, is a mirror, which is shown in section at M, fig. 4 ; to balance the 
weight pf this mirror, and adjust the magnets in a horizontal position, a brass washer, 
W, is caused to move along a screw, until a point is attained at which its weight has 
brought both the magnets into the same horizontal plane. There is also another 
adjustment, which permits of the magnets being brought closer together or separated 
more widely asunder. The motions of the compound magnet are observed by means 
of a distant scale and telescope, according to the method applied to the magneto- 
meter of Gauss. The rectangle da, d'a', fig. 2, is the outline of a copper damper, 
which, owing to the currents induced in it by the motion of the magnet, soon brings 
the latter to rest, and thus expedites experiment. 
It is well known that one end of a magnet attracts, while the other end repels the 
