ON THE FLO IV OF SOLID CODIES. 267 



M. Trcsca. He has worked out a subject which was very little known 

 ~ hardly conceived of, in fact, in any form whatever before, he took it 

 up, and commencing by giving us the results of his experiments, he has 

 drawn one deduction after another, and his subject has extended into 

 one which promises to be of very great importance indeed in mechanical 

 science. I cannot follow him into physiology, because I am not suffi- 

 cient physiologist to say whether our nails are forced out of us in the 

 manner M. Tresca has described ; but it is my want of apprehension, 

 no doubt, rather than his want of perfect conception which is at fault. 

 M. Tresca, by his investigation, throws down as it were the boundary 

 line between solids and liquids, a solid, according to his view, being 

 only a liquid with greater viscosity, and this is an enlargement of our 

 general conception of matter which cannot fail to be of practical im- 

 portance in mechanical science. With these few observations, I beg to 

 call upon you to pass a hearty vote of thanks to M. Tresca. 



Mr. J. SCOTT-RUSSELL, F.R.S. : I beg to second the vote of thanks, 

 and, in saying so, allow me to say, from my own observation, that M. 

 Tresca has given to this meeting to-day, in comparatively few words, 

 the whole result of some nearly twenty years of continuous thought 

 and continuous experiment devoted to this subject, in the most admi- 

 rable and methodical way. I have watched his progress for that 

 number of years with the deepest interest, and I cannot tell you how- 

 profound a gratification it was to me to find that all this was to be 

 brought before you to-day. And allow me to say this : that in addition 

 to washing away the curious and narrow prejudice in which our minds 

 are bound as to the radical difference between a solid and a fluid, and 

 we must get rid of this prejudice in order to go further in the matter of 

 science he has paved the way for enormous improvements in the 

 important arts of metallic manufactures. He has given us the key to 

 make out of every kind of metal, on the first occasion in which it is 

 lignified, every kind of body to which we may wish it afterwards to be 

 converted. Whereas we, in our clumsy way, up to the present time, 

 take a body of metal, melt it, and then cool it ; and then to make a 

 little change in it, heat it again, and cool it again ; and then to make 

 another little change in it, heat it again, and again cool it. But he 

 now tells us that you have only to communicate to a little bit of melted 

 metal, the first day it comes to the state of metal, what you want it to 



