162 ANNUAL OF SCIENTIFIC DISCOVERT. 



extent that, if iinchecked, it would in course of time be so great 

 fis to destroy the insulation of the wire. To obviate this, I have 

 perforated the two poles of the elcctro-mas-net as close as possible 

 to the armatures, and a stream of cold water circulates twice 

 round the machine. This carries off the heat in a most effective 

 manner, and no appreciable detriment in its electrical results oc- 

 curs. I have not yet ascertained the quantity of the mixed gases 

 ofiven off" per minute, but it is most interesting to notice the con- 

 tinuance of the decomposition of water which takes place for some 

 seconds after all motion in the machine has ceased." 



He did not wish it to be inferred that the sole cause of heat was 

 the elongation of the iron. Doubtless the electric currents pass- 

 ing through the wire would produce heat; but he believed that 

 the quantity of heat produced by that means was small as com- 

 pared with that produced by the elongation of the iron itself. He 

 entertained this opinion for the following reason : They had lately 

 applied one of these magneto machines, driven by steam power, 

 in connection with a large inductoiium, giving about 18-inch 

 sparks ; and after a few hours' work it had been found that the 

 copper or primary wire surrounding the core of the coil appeared 

 to be quite cool, while the iron core itself was considerably heated. 

 He therefore mainly assigned the production of the heat to the 

 cause he had specified. 



Mr. C. W. Siemens believed that the chief cause of the heat 

 which was developed must be attributed to currents, because the 

 same cause which sets up a current in the coil surrounding the 

 electro-magnets will naturally set up a current, in the copper it- 

 self, large in proportion to the greater area open for the passage 

 of the current ; and the heat developed will also be large in pro- 

 portion to the less conducting power of the iron as compared with 

 the copper. In order to test this, he had one of the long keepers 

 notched in the edges, and by that means he obtained a greatly 

 reduced heating action, thouo;h he could not entrely obviate it. If 

 his view were correct, — that the heat was due to currents in the 

 armature, — then it could not be entirel}^ obviated, because they 

 must not separate the armature, as that would destroy the con- 

 tin uit}^ ; they could onl}^ notch it. To his own mind, the theory 

 that the heat was produced by elongation of the metal was not at 

 all satisfactory. If, however, currents would not explain the phe- 

 nomenon, they must look rather to some other action in metals, 

 produced by magnetism, than seek to explain it by the mechanical 

 elongation and compression of the metal. 



EFFECT OF THE GALVANIC CURRENT UPON THE TENACITY OF WIRE. 



Mr. James Wylde has made public the results of some experi- 

 ments which are of great importance to telegraphic science. He 

 says that he found, some years since, that when intense currents 

 were passed through the best copper wive, in only one direction, 

 its tenacity was gradually destroyed, so that it could finally be 

 crushed to pieces by the lingers. This loss of tenacity occurred 



