Mechanical Science, 165 



it became a point to ascertain whether the masses of metal were 

 regularly crystallized. By cutting plates in different directions, 

 from different parts of the same mass of lead, and examining their 

 nodal lines, they did not agree with each other, and it appeared 

 that a mass of metal, considered as a whole, does not possess the 

 structure or properties of a body regularly crystallized, though 

 each plate cut from it acts as if it belonged to such a body. And 

 even if a large plate, which resembles a regularly crystallized sub- 

 stance, be cut up into smaller plates, these, by trial, will almost 

 constantly be found to differ from each other. 



These and other facts shew clearly that the metals have not a 

 homogeneous structure, and yet at the same time that they are not 

 regularly crystallized, but that they have a sort of semi-regular 

 structure, as if, at the moment of solidification, several internal dis- 

 tinct crystals were formed, considerable in volume, but not having 

 their homologous planes parallel to each other, so that, though each 

 crystal is of regular structure, the whole mass is confused. 



By examining crystallizations of metal, and especially of lead, 

 obtained in the usual way from quantities in the act of solidifying, 

 by pouring off the remaining fluid portion, this will easily be seen 

 to be the case; and the distinct systems of crystals will be found 

 to be the more extensive, the longer the time the metals have been 

 retained in fusion, or the more frequently they have been fused. 



A consequence of this structure is, that greater differences of 

 elasticity will be observed in the same substance, by taking small 

 plates than by using large ones, because then the number of crystals 

 taken into the plates will be less. For the same reason a mass of 

 metal examined in this manner will appear to be more regular in 

 its structure as the mass is smaller. 



Whether the plates of metal be taken from a large mass, or cast 

 in moulds of the proper size, does not appear to make much differ- 

 ence ; plates obtained in both ways will sometimes differ little, and 

 sometimes much. The substance of the mould, its position, or the 

 place of the jet by which the metal enters, appears to have no in- 

 fluence over the elasticity of the resulting plate, i. e. there is always 

 one direction in which the resistance to flexure is the greatest. 

 Neither does sudden cooling, nor the passage of an electric current 

 along one of its diameters whilst in fusion and cooling, exert an ap- 

 preciable effect on the phenomena ; but the case is very different if 

 a series of small blows be given to the mould as the metal solidifies : 

 the formation of large crystalline systems is almost always then dis- 

 turbed, and the resulting mass is of such uniform elasticity, that 

 plates formed from it give only one sound, and the two nodal dia- 

 meters can be produced across any part of it. It would be as in- 

 teresting as important, to ascertain if the metals, whose crystalliza- 

 tion has been thus disturbed, have a tenacity equal to what they 

 acquire under ordinary circumstances, and whether they do not 

 acquire some new properties which may render this process useful 

 in the arts. 



