256 SECTION MECHANICS* 



iron, all the accidents of the various processes which have been used 

 for its formation. You can, indeed, in smelting, make these filaments 

 expand or concentrate them ; you can unite or separate them ; but you 

 cannot make them disappear ; and we have here another mode of 

 investigation, which must be made use of for the study of the interior 

 convolutions which correspond to certain exterior changes of shape. 



When once all the relative displacements, as well as the force 

 necessary to produce them are known, there will be no great difficulty 

 in determining the best way of carrying them out, and of calculating 

 the mechanical work which it will demand. 



In one of our smelting experiments, made on a large scale upon 

 brightened platinum, an accessory phenomenon presented itself, which 

 attracted the whole of our attention, and which is so closely connected 

 with the deformation of solid bodies, that you will allow me, I am 

 sure, to say a few words about it, although the experiments which have 

 originated from it are not yet finished. It is, moreover, a great satis- 

 faction to me to be able to communicate to a gathering of English 

 scientific men the first results of these experiments, before any publi- 

 cation whatever of them has been made. 



On the 8th of June, 1874, we only pointed out to the Academy of 

 Sciences "the principal fact : when the bar of platinum, at the moment 

 of smelting, had already cooled down to a temperature below that of 

 red heat, it has happened several times, that the blow of the stamp 

 hammer which occasioned, at the same moment, in this bar, both a 

 local depression and a lengthening, heated it anew along two inclined 

 lines, forming upon the sides of the piece the two diagonals of the 

 depressed portion, and this re-heating was so great, that the metal along 

 these two lines was brought back to the red hot temperature, plainly 

 enough for its form to be distinguished. These lines of greater heat 

 even remained luminous for several instants, and presented the 

 appearance of the two jambs of the letter X. In some cases we have 

 been able to count simultaneously as many as six of these X, produced 

 one after the other, as the bar under operation was being moved, in 

 order to draw it out by degrees to a certain part of its length. 



The explanation of these luminous traces could not for an instant 

 be doubtful ; the lines of greater slipping were, at the same time, the 

 zones of greater developed heat, and we had before us a perfectly definte 



