5() Prof. D. E. Hughes on an Induction-balance. 



If we now move this bar until it rests on the centre^ of 

 either coil, we find that at this point the bar has no disturbing 

 effect whatever, and although the coils at its maximum line 

 of force are sensitive to the finest iron wire, a very large mass 

 of iron or a rod of 1 centimetre diameter has no disturbing 

 effect whatever. Its paralyzing effects are so remarkable, that 

 if we place a flat piece of iron or other metal across the maxi- 

 mum line of force, where loud sounds are given out, the 

 instant that this flat piece is moved, so that one or both edges 

 touch or end in the minimum line of force, it becomes in- 

 stantly neutralized, giving out no sound whatever, notwith- 

 standing that a large mass of metal lies in the maximum line 

 of force. We will now demonstrate by experiment the ex- 

 ceeding sensitiveness of the induction-balance to the smallest 

 piece of metal, if it is in the maximum line of force, and no 

 part of it touching the minimum ; and also that by allowing 

 either or both ends of this or a very large piece of metal to 

 cut or end at the minimum lines of force, complete paralysis 

 and consequent silence are produced*. 



VI. There is a marked difference of the rapidity of action 

 between all metals, silver having an intense rapidity of action. 

 The induced currents from hard steel or from iron strongly 

 magnetized are much more rapid than those from pure soft 

 iron ; the tones are at once recognized, the iron giving out a 

 dull, heavy smothered tone, whilst hard steel has tones ex- 

 ceedingly sharp. If we desire to balance iron, we can only 

 balance it by a solid mass equal to the iron to be balanced. 

 No amount of fine wires of iron can balance this mass, as the 

 time of discharge of these wires is much quicker than that of 

 a larger mass of iron. Hard steel, however, can be easily 

 balanced not only by steel but by fine iron wires, and the 

 degree of the fineness of these wires required to produce a 

 balance gives a very fair estimate of the proportionate time 

 of discharge. The rapidity of discharge has no direct relation 

 with its electrical conductivity; for copper is much slower than 

 zinc, and they are both superior to iron. 



We find that the induction-balance is exceedingly sensitive 

 to all molecular changes which take place in all metals sub- 

 jected to any of the imponderable forces. Thus we have 

 already by its aid studied the effects on metals of heat, 

 magnetism, electricity, &c, and of mechanical changes such 

 as strain, torsion, and pressure ; and I propose in some future 

 paper to describe the remarkable results already obtained, and 

 to demonstrate by experiment today to the Physical Society 

 the results of these forces upon the induction-balance. 



* This was fully demonstrated to the audience by numerous experi- 

 ments. 



