C. GENERAL PHYSICS. 159 



five years. Bulletin Soc. Imp. des JSFaturalistes^ 3Ioscoiv, 187 4^ 

 310. 



THE DISTEIBUTION OF MAGNETISM IN A MAGNET. 



The investiojations bv Jamin on the distribution of magj- 

 netism in solid and compound magnets have already been 

 fully noticed by us ; the latest paper on this subject is by 

 Professor Rowland, of the John Hopkins University at Bal- 

 timore, who states that some investi2;ations of his owm made 

 in 1870 and 1871, and which have not been published as yet 

 owing to reasons beyond his control, bear directly upon the 

 points investigated by Jamin and others, and he has there- 

 fore begun the publication of them in full. He begins by 

 giving the mathematical theory of the distribution of mag- 

 netism. His formula may be considered, he says, simply 

 as the development of Faraday's idea of the analogy be- 

 tween the magnet and the voltaic battery immersed in 

 water, and are similar to those of Jamin and Green, but 

 have the advantage of being obtained in a more simple 

 manner than Green's, and, w4iat is of more consequence, all 

 the limitations are made at once, after which the solution 

 is exact ; so that, although they are only approximate, yet 

 we know just where they should differ from experiment. 



One of the most novel features of the observational part 

 of Professor Rowland's work consists in the method itself, 

 by means of which he measures the intensity of the mag- 

 netism at any portion of the magnet. This consists in slid- 

 ing a small coil of wire which just fits the bar, and is also 

 very narrow, along the bar, inch by inch, and noting the in- 

 duced current by the deflection of the galvanometer needle. 

 American Joinmal of Science and Arts, X., 325. 



ON THE DISTRIBUTION OF MAGNETISM IN SHORT THICK 



MAGNETS. 



A second series of investigations has been made by Jamin 

 in reference to the distribution of magnetism in compound 

 ma2:nets havinsj a finite lencrth. The formula for this case 

 can be deduced theoretically from those of his previous 

 papers, as applicable to bars of infinite length ; and having 

 taken this step, it remained only for him to verify this law 

 by actual experiments. This he has done by employing, as 



