224 Royal Imtitution. 



of an inch from the axial line of the magnetic field, and the second, 

 the place in Centigrade magnetic degrees below water. 



Fhnt-Glass. 



0-3- 91 

 0-4-10-6 

 0-5-111 

 0-6-11-2 

 0-7-121 



Heavy Glass. 



0-3-37*8 

 0-4-38'6 



Bismuth. 



On-1871 

 10-2734 



0-6-400 I 1-5-3626 



0-8-48-6 



10-51-5 



12-65-6 



The result here is that the greater the distance of the diamag- 

 netic bodies from the magnet, the more diamagnetic is it in relation 

 to water, taking the interval between water and air as the standard : 

 and it would further appear, if an opinion may be formed from so 

 few experiments, that the more diamagnetic the body compared to 

 air and water, the greater does this difference become. At first it 

 was thought possible that the results might be due to some previous 

 state induced upon the body, by its having been nearer to or further 

 from the magnet ; but it was found that whether the progress of the 

 experiments was from small to large distances, or the reverse ; or 

 whether, at any given distance, the object was previous to the mea- 

 surement held close up to the magnet or brought from a distance, 

 the results were the same ; — no evidence of a temporaiy induced 

 state could in any of these ways be found. 



It does not follow from the experiments, if they should be sus- 

 tained by future researches, that it is the glass or the bismuth only 

 that changes in relation to the other two bodies. It may be the 

 oxygen of the air that alters, or the water, or more probably all these 

 bodies ; for if the result be a true and natural result in these cases, 

 it is probably common to all substances. The great point is that 

 the three bodies concerned, air, water, and the subject of the expe- 

 riment, alter in the degree of their magnetic relations to each other ; 

 at different given distances from the magnet the ratio of their mag- 

 netic power does not, according to the experiments, remain the 

 game ; and if that result be confirmed, then it cannot be included by 

 a law of action which is inversely as the square of the distance. A 

 hydrometer floating in a fluid and subject to the gravity of the earth 

 alone, would (other things being the same) stand at the same point, 

 whether at the surface of the earth, or removed many diameters of 

 the earth from it, because the action of gravity is inversely as the 

 square of the distance ; but if we suppose the substance of the hy- 

 drometer and the fluid to differ magnetically, as water and bismuth 

 does, and the earth to act as a magnet instead of by gravity, then 

 the hydrometer would, according to the experiments, stand at a dif- 

 ferent point for difterent distances, and if so could not be subject to 

 the former law. 



I'he cause of this variation in the ratio of the substances one to 

 another, if it be finally proved, has still to be searched out. It may 

 depend in some manner upon the forms of the lines of magnetic 

 force, which are different at difl^erent distances ; or not upon the 



