190 



Prof. D. E. Hughes. 



[May 10,. 



means not only perceive the strain but determine its direction by the 

 polarity obtained. I have no doubt but that some day this will be 

 practically applied to the appreciation of strains in iron shafts or 

 cannons. 



If we apply torsion to a soft iron rod, we find the degree of rotation 

 equal at each section observed, quite independent of its length, con- 

 sequently we find perfect symmetry of rotation throughout. If we 

 magnetise the rod in such a manner as to leave its residual magnetism 

 with several consequent poles, the portions into which the rod is 

 thus divided are similar in their symmetry to several distinct magnets 

 with their similar poles placed opposing each other, producing 

 reversed induced currents at each consequent pole. 



When we take observations by the induction balance, either upon 

 electric conductivity or magnetism, we do not observe the effects as 

 generally observed by other methods, viz., after the current has had 

 time to reach its stable condition ; we really observe the effects pro- 

 duced during the first instant of time, known as the variable period y 

 observing from the first instant of electrical contact to a certain 

 maximum, which can never be greater than the length of time of 

 these contacts. These results are obtained by the rapid contacts of 

 the rheotorae, producing 500 vibrations per second, which the ex- 

 tremely rapid action of the telephone allows us to appreciate. Thus, 

 the actual duration of the electrical contact is but yoVo P ar ^ °f a 

 second ; and this proves the extremely rapid action of molecular 

 rotation, as the effects which we have noticed are all produced in this 

 fraction of a second. 



Magnetic Conduction. 



The following experiments were made by means of an induction 

 balance of four and three coils, described fully in my paper, " Proc^ 

 Roy. Soc," vol. 29, p. 56, 1879. The following diagram shows its 

 electrical communications. 



