188 L. M. ( 1>> > snntn — Kif'rrt of Mechanical Hardening 



12. Before leaving this part of the subject the result of 

 some experiments should be stated, which were made to ascer- 

 tain what care was necessary to be taken to prevent a loss of 

 magnetism while the magnets were being adjusted, etc. A 

 large loss of magnetism was observed in all cases when the 

 magnets were subjected to any sudden jarring ; so that, as may 

 be seen from the following table, great care had to be exercised 

 between the magnetization and the determination of the mag- 



mechanieally hard 



As is well known the heat-hardening does much to render a 

 magnet less sensitive to jarring, etc. ; it was not discoverable, 

 from the experiments made, that the mechanical hardening 

 produces even in a small degree a similar effect. 



II. — Experiments with unsaturated Magnets. 



13. Apparatus. — The apparatus was arranged as is usual in 

 cases where the temporary magnetic moment is to be deter- 

 mined by the deflection of a magnetometer needle; the method 

 having been so often described by others,* it would seem un- 

 necessary to enter into any minute description here. 



The effect of the magnetizing helix on the magnetometer 

 was counterbalanced by a second one, the helices being placed, 

 the one to the north, the other to the south of the instrument. 

 The course of the current was as follows : from the battery 

 through the two coils and a variable resistance to a key, and 

 finally through a tangent-compass back to the battery. 



By means of a com mutator, the direction of the current in 

 the tangent compass could be reversed. 



The constants of the magnetizing helix were as follows : 



External radius 52 



As an accurate and at the same time convenient method of 



adjusting the magnets, a glass tube, with an internal diameter 



* Compare R r. Dortmund, 



