1826.] Magnetism of MetalSfS^c, arising from their Rotation, 191 



mode of action, therefore, affords us a means of magnifying small 

 magnetic susceptibilities, which may hereafter prove very- 

 valuable. 



To illustrate this more strongly, we suspended a brass disc of 

 2*25 inches in diameter, and 0*15 inch in thickness, as in the 

 last case, and noted the time of its performing successive revo- 

 lutions as follows : 



1 rev. 2 rev. 3 rev. 4 rev. 5 rev. 



20^-2 29-1 35-2 40-8 45-7 



It was now cut, as in the last case, but it being necessary for 

 this purpose to use a saw, the abraded portions, which were 

 pretty copious, were strewed over it with the intervention of a 

 piece of thin paper, to obviate the effect of loss of weight, as 

 nearly as might be. The times were now found increased as 

 follows : 



being almost exactly doubled, and of course the force was 

 reduced in the ratio of about 4 to 1. 



The cuts were now cleanly soldered with bismuth; and 

 though, as we have seen, the direct force of bismuth is so small 

 as to be scarcely perceptible, yet its indirect effect in restoring 

 the magnetism of the brass was such as to cause the same arcs 

 to be described in the following numbers of seconds : 



which require the exertion of an accelerating force more than 

 double that developed in the last trial. 



The bismuth was now melted out, and the cuts being carefully 

 washed with melted tin, were filled with fresh tin, which was 

 allowed to fix, and the disc being trimmed, and replaced, the 

 times were now found to be 



21-7 30-8 38-0 43-5 48-7 



The restoration of energy, as in the case of the copper disc, is 

 here very manifest, the times of rotation being nearly reduced to 

 their original magnitude. The comparison of these gives for the 

 accelerating forces 



Brass, uncut 1*00 



cut 0-24 



soldered with bismuth 0*53 

 soldered with tin ... . 0*88 



Copper, uncut 1*00 



cut 0-20 



soldered with tin 0*91 



The effects of solderins; with lead and with fusible metal 



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