involved in the Construction of Artillery. 355 



But an additional argument may be drawn from Professor William Thompson's views 

 as to the nature of the forces concerned in thermo-electric currents, from which it would 

 seem to follow that iron, or any other body in which a thermo-electric current can be 

 excited, can have none other but a crystalline arrangement (Thompson, " Dynamic Theory 

 of Heat," Phil. Mag., 185G.) 



In addition to the several examples quoted in the text (sects. 9-15), of the arrange- 

 ment of crystalline axes perpendicular to the bounding planes of the solid, I would remark 

 a very interesting one, given by the late Professor Daniell, " Elem. of Chem. Phil.," 

 sect. 117, p. 88: — If a parallelepiped of tin — hammered or cast, matters not — be placed in 

 mercury for some time, the latter is absorbed gradually: it enters the mass by successive 

 plane couches, parallel to its surfaces; expansion is produced in the planes of these couches, 

 and hence lines of least pressure perpendicular to the same. After a time, the parallele- 

 piped is found split up into six pyramids, by planes penetrating from its edges, and inter- 

 secting within it, — their bases being the original sides of the solid; and each of these 

 pyramids is found composed of crystals, whose longest axes are arranged perpendicular to 

 the original sides, and parallel to each other ; and into these integrant crystals each pyramid 

 may be subdivided. 



Here is a case in which chemical change — resulting in the formation of, no doubt, a 

 definite amalgam — has, owing to the peculiar circumstances of its formation in a state of 

 crystalline aggregation, produced an effect similar to that which mere change of tempera- 

 ture might have induced in the parallelepiped of tin, had the latter been originally crys- 

 talline, or large enough for internal strains to have so arisen. 



Again, the following curious experiment, made by myself several years since, but not 

 previously published : — If a portion of Muutz patent rolled yellow metal (Table xr.. No. 12, 

 in text), in the state in which it is used in commerce for ships' sheathing, bolts, &c. — namely, 

 in which it is tough, malleable, extremely flexible, and endowed with a distinct fibrous 

 arrangement in the direction in which it has been laminated or rolled; — if of this a small 

 rod, or a narrow slip, be cut from a sheet, and plunged for a moment or two in a tolerably 

 strong solution of nitrate of mercury, and then withdrawn, washed, and wiped dry, — it will 

 be found that it has almost instantaneously become rigid, and so brittle that it may now 

 be broken into short bits between the fingers, whereas, previously, reiterated bending 

 backwards and forwards, between the hands, would have with difficulty broken it at all. 



The surface of the metal is found slightly amalgamated ; its fractures present crystalline 

 planes, penetrating the solid in directions perpendicular to its faces; and, on examination 

 of the fracture with a lens, an extremely superficial, but real, penetration of the mercury 

 between the surfaces of the crystals will be observed to have occurred. 



The conditions here were different from the former experiment: the phenomena occur 

 with much greater, indeed with truly remarkable rapidity, the transmutation from tough- 



