﻿Magnetizing and Astaticizing Galvanometer-Needles. 487 



liberal allowance for the influence of these changes, the sensi- 

 tiveness was increased fully ten times by the remagnetization. 



This would seem to indicate either that the first magneti- 

 zation had been very inefficient, or that the needle in transit 

 from Philadelphia to Washington had been accidentally sub- 

 jected to some very strong demagnetizing influence. It 

 serves to show, however, the importance and necessity of 

 some such ready and efficient means of remagnetizing the 

 systems of galvanometers in which a high degree of sensi- 

 tiveness and not absolute constancy is required. Steel mag- 

 netized to the degree of intensity here attained will of course 

 gradually lose a part of its magnetism, but not more (in my 

 experience) than 10 or 20 per cent, in many months, if care- 

 fully handled. This small loss is not of importance compared 

 with the gain in sensitiveness secured, as the original strength 

 may at any time be quickly and easily restored or even slightly 

 increased* by remagnetization. 



The advantage of the method which specially commends it 

 to general laboratory use is the simplicity of the apparatus 

 required. The whole arrangement may be made in any labora- 

 tory in a single afternoon. The same electromagnets may be 

 used for systems of varying dimensions by adding adjustable 

 pole-pieces. But if many systems are to be treated, a more 

 convenient although more elaborate arrangement, like that 

 shown in Plate XIII. figs. 3 & 4, will be desirable. In this 

 the magnetic system is held lightly between two long jaws 

 of copper a, a, adjustable in width by means of the screw b. 

 An adjustable fork or table c, which may be replaced by a 

 clamp if desired, serves to carry the fibre support. 



The two halves of the electromagnet, wdiich may be wound 

 as before, or with four coils as here shown, are carried on 

 arms d } e, pivoted at /, so that they may be easily swung 

 apart or brought together, the motion being made sym- 

 metrical with respect to the jaws a, a by means of the 

 links and sliding block. The lower set of poles are adjust- 

 able on the yokes for systems of different lengths, and the 

 whole is mounted on an L-shaped base, which may be placed 

 so that the needle is either vertical as shown in the figure, or 

 horizontal. 



This method has also been applied with much success to 

 the initial magnetization of some new systems for the same 

 galvanometer already described, and for the new very sensi- 

 tive one which is described in a subsequent paper. A further 



* Up to a certain point repeated magnetization increases the perma- 

 nent magnetism. See experiments of Fraukenheim, Pogg. Ann. cxxiii. 

 (1864); and Fromnie, Pogg. Ann. vii, (1875), Wied. Ann. iv. (1878). 



