Dr. Laniont on the most advantageous Form of Magnets. 371 



The principles above stated are here only mentioned en passant, 

 as they have been already on an earlier occasion * stated, at least 

 in outline, and will be hereafter more fully explained in a more 

 detailed memoir. It has been already stated above, that the 

 more or less advantageous form of a magnet is to be decided by 

 the proportion of the magnetic moment to the mass, and to the 

 moment of inertia : now, as to the last, it only comes into consi- 

 deration in the oscillations, and it is of more trifling significance, 

 on which account we will first investigate the proportion of the 

 magnetic moment to the mass. 



1st Series of Experiments. — In order to ascertain the depen- 

 dence of the magnetism upon the diameter, I caused to be 

 prepai'ed four pieces of iron (Plate VI. fig. 4) of equal length 

 = 43'"-2 (Paris measure), and equal weight, but different trans- 

 verse sections; the sections were, — 



Of A, an equilateral triangle; length of one side = 7'"'5. 



Of B, a circle; diameter = 5 '"-7. 



Of C, a square ; length of one side = 5 W, 3. 



Of D, a parallelogram ; sides == 6"'-0 and 4"'*1. 



Of E, a parallelogram; sides = 12"'-4 and 2"'-l. 



In a long spiral of 212 turns, these pieces of iron,, inserted as 

 cores, gave the following magnetic moments (reduced to equal 

 strength of current) : — 





Magnetic moment. 



Mass. 



Proportion. 



A 



. . 7-255 



1-00 



7-255 



B 



. . 6-806 



0-99 



6-875 



C 



. . 7-300 



114 



6-404 



D 



. . 6-952 



1-05 



6-621 



E 



. . 8-248 



1-13 



7-299 



how little foundation there is for the ordinary opinions may be seen from 

 the following statement. 



In the mechanical workshop of the observatory of this city are two 

 magnetizing apparatus, of which the one consists of two 25-pound bars, 

 and the other is an electro-magnetic apparatus of great energy. Amongst 

 the experiments which were carried out to prove the relation of the two 

 apparatus appears the following case. 



Two prismatic magnets, length 5G" r, and 56"'*6, breadth 6'"'8 and 4"' - 9, 

 thickness 1'"'5 and l" f -0, perfectly hard, were magnetized with the 25-pound 

 bars, and the magnetic moment was determined by means of the devia- 

 tion, whereby I obtained — 



Greater Magnet, deviation 116"3 scale-divisions. 



Smaller Magnet, deviation 81*7 scale-divisions. 



Afterwards, when the two needles had been magnetized by means of the 

 electro-magnetic apparatus, there resulted — 



Greater Magnet, deviation 1 77'B scale-divisions. 



Smaller Magnet, deviation 112 - 4 scale-divisions. 



From this we see that the magnetizing by the 25-pound bars, in regard to 

 the degree of saturation, was deficient, in the greater magnet by somewhat 

 more, and in the smaller by somewhat less, than a thud part. 

 * Jahresbericht der M'unchener Sternwarlcftir 1854, p. 2/. 



