130 ANNUAL OF SCIENTIFIC DISCOVERY. 



" 1. AH bodies become magnetic, as soft iron does, under the influence 

 of a magnet, but in greater or less degree according to their nature. 



^j ' cp Cj O 



13. The temporary magnetism of a body does not depend upon its 

 mass, but on the manner in which the ether is distributed in the body. 

 3. A substance is drawn towards a magnetic centre by the difference 

 of the actions exerted upon the substance and upon the volume of the 

 medium displaced by it." The effects were measured by the tension 

 developed upon small bars of the various substances by an enormous 

 electro-magnet. The continual oscillations are prevented by suspend- 

 ing under each bar a small sphere of lead or zinc, immersed in water 

 or a solution of chloride of calcium. 



" Measuring, in this way, the actions exerted upon substances mov- 

 ing in different media, I convinced myself of the enormous influence 

 exerted by the surrounding medium. Thus, common glass, which in 

 the air is attracted by the t\vo poles of a magnet, is strongly repelled 

 by these same poles when in solutions of iron or nickel; sulphur and 

 white wax, which in the air are repelled by the centres of magnetic 

 action, are attracted when they are immersed in concentrated solutions 

 of chloride of calcium or chloride of magnesium." Upon the third 

 general law announced above, he says, " Thus, a body is attracted 

 or repelled by a magnetic centre, according as it is immersed in a 

 medium less or more magnetic than itself. Hence it results that the 

 attractions and repulsions exerted upon different bodies by either pole 

 of a magnet near which they are brought, depend upon the same 

 cause, and not upon two orders of phenomena." To explain the fact, 

 that all bodies are not attracted in xacito, and that some substances are 

 almost as much repelled in vacua as in air, " it is necessary to admit 

 that the ethereal medium by means of which magnetic actions are 

 transmitted is influenced in the same way, but in a different degree, in 

 a void space and in one containing matter ; and that a void space be- 

 haves like a medium more magnetic than the substance which is most 

 repelled, that is to say, bismuth. Certain gases, as nitrogen, nitrous 

 oxide, &e., experience no appreciable action from magnetism, but 

 oxygen does, and the slight magnetic power of the air is due solely to 

 the presence of oxygen. I found that a small bar of charcoal, which 

 ha? condensed oxygen, oscillates between the poles of a strong mag- 

 net like a small magnetised bar, whilst in xacuo it is generally repelled, 

 and always feebly influenced, by the action of magnetism." 



" Comparing the power of oxygen with that of iron, we conclude 

 that 10.78 cubic feet of air has an action represented by 1.65 grain 

 of iron. If we reflect that the earth is surrounded by a mass of air, 

 equal in weight to a stratum of mercury 30.4 inches in depth, it may 

 be asked whether such a mass of magnetic gas does not interfere in 

 the phenomena dependent on terrestrial magnetism, and perhaps in 

 the diurnal variations of the magnetic needle ; and if we calculate the 

 magnetic power of this fluid ma&s, we find it equivalent to an im- 

 mense sheet of iron, rather more than 0.004 of an inch in thickness, 

 and covering the whole surface of the globe." The author concludes 

 by saying, "I do not, therefore, admit any difference between dia- 

 magnetism and magnetism proper." 



