326 Mr. T. Gray on the Experimental Determination 



No. of Magnet. Value of II. 



1. 5379 



2. -15412 



3. -15422 



4. -15405 



5. -15375 

 Mean value -15399. 



In the determination of the magnetic moments no correc- 

 tion of the value of H was made for induction. 



The magnets were then magnetized a second time by means 

 of the current from twenty double tray-cells flowing through 

 a magnetizing coil of the same length as the magnets, con- 

 sisting often layers of wire of severity turns each, and having a 

 resistance of 2*15 ohms. By the same method as before, the 

 magnetizing force is found to be 1100 nearly. For ease of 

 comparison, the moments of the magnets after the first and 

 second magnetization are placed side by side in the Tables of 

 results. They show that the magnetizing force first employed 

 nearly saturated the bars. A few of these magnets were 

 placed between the poles of a powerful Ruhmkorff magnet, 

 when the increase of magnetism was found to be very small. 

 It will be observed from the Tables of results that one or two 

 of the magnets showed that their magnetic moment had been 

 diminished by the second magnetization. This may have 

 been due to some accident ; but the results have been entered 

 in the Tables as they were obtained. 



To show the relative effects of different magnetizing forces 

 on bars tempered glass-hard and a blue," two bars were 

 brought one to each of these tempers, and were then magne- 

 tized, first with a very small magnetizing force, which was 

 increased by small measured amounts, and observations of the 

 magnetic moments of the bars made at each increase. The 

 results are shown in the annexed curves (Plate V.), of which 

 the upper corresponds to the blue-tempered, and the lower to 

 the glass-hard magnet. The abscissae are proportional to mag- 

 netizing forces, and the ordinates to magnetic moments. It 

 will be observed from the curve that for every magnetizing 

 force the magnetic moment of the blue-tempered magnet is 

 greater than that of the glass-hard magnet, and that the differ- 

 ence between them diminishes as the magnetizing force is in- 

 creased. 



As will seen from the appended Tables, the results show 

 that magnets made of steel which had been previously 

 heated to a bright red and cooled suddenly in cold water, 

 were scarcely so strong, after the first magnetization, as those 

 (made of the same steel) which, after having been so treated, 



