190 Messrs, Babbage and Herschel on the [Sept. 



Fig. I. Fig. 2. Fig.S. 



Fig. 4. 



Fig. 5. 



The times observed and forces deduced in the several cases 

 were as follows : 



Similar effects were observed in other metals, but in different 

 degrees. For instance, in the case of soft tinned iron, the same 

 number of cuts, made in the same manner, produced a very- 

 slight diminution of force, while in copper the effect of the same 

 operation was to reduce the force in the ratio of 1 to 0"20. 



A thin disc of copper suspended at a ^iven distance over the 

 revolving magnet, performed six revolutions from rest in .54^*8. 

 It was then cut in eight places in the direction of radii nearly up 

 to the centre and 45^ asunder, by which operation its magnetic 

 virtue was so weakened, that it now required 121**3 to execute 

 the same number of revolutions. The cuts were now soldered 

 up with tin, and the magnetic action was now found to be so far 

 restored as to enable it to perform its six revolutions in 57'-3, 

 that is to say, very nearly in the same time as when entire. This 

 is the more remarkable, since tin, as we have seen, is not above 

 half so energetic as copper when acting directly. This indirect 



