172 Mr Watt on the Magnetic Injluence of the Solar Rays. 



the westward than the common compass needle. As the ten- 

 dency of the north poles of these magnets was to verge towards 

 the west, in the direction of the variation, when placied under 

 these circumstances, it seems to favour the idea that the cause 

 of the variation is distinct from the law which gives to the mag- 

 netic needle its polarity. 



It appears that, when the magnetic needle finds itself in what 

 may be termed a new situation in respect to the influence that 

 may affect it, a considerable time is often necessary before it can 

 adjust itself to those alterations, making sufficient allowance for 

 the time it would take to settle, when any way set in motion. 



This is exemplified by fixing two magnetic bars on the 

 circumference of a circle, at the distance of 90° from each 

 other, the circle being suspended by a hair from the centre ho- 

 rizontally, and balanced so as to move round easily ; and the 

 two north poles of the bars placed outwards, and the south poles 

 pointing to the centre of the circle, in the direction of the radii. 

 If the north pole of a powerful magnet is placed between the 

 north poles of the bars, at the distance of two inches on a sepa- 

 rate stand, they commence to vibrate, and the alternate repul- 

 sion of the magnetic bars by the third magnet, causes the circle 

 to oscillate for nearly half an hour ; and, when it ceases, the re- 

 pelling magnet, if the needles are equal in power, will be exact- 

 ly between them. If one is stronger than the other, the strong- 

 est will be farthest off*. The same phenomenon would take place 

 in an inverse ratio, if an attracting magnet was introduced 

 between the bars ; the strongest resting nearest the attractor. 

 This is too refined an experiment to be shewn by a common 

 magnet, but is exhibited by considering the north pole a large 

 magnet. If we place two magnetic bars across each other at 

 right angles upon a piece of cork, swimming in water, the 

 strongest needle will rest nearest the north, if alike equidistant 

 from it. 



Though the pointing of the needle was altered by its being 

 surrounded by wax, it did not lessen its sensibility to the power 

 of other attracting bodies ; but seemed, on the contrary, rather 

 to increase it, by leaving it more free from the influence of the 

 polar attraction. One object I had in view, by diminishing the 

 polarity of the needle, without interposing any other attracting 



