264 ANNUAL OF SCIENTIFIC DISCOVERY. 



pendicular to the cooling or heating surfaces of the solid ; that is, in the 

 lines of direction of the heat wave." He assumes, that as a gun, in cooling, 

 radiates heat from the centre outward, in all directions, the particles arrange 

 themselves in radial lines, ready to be separated on the application of a com- 

 paratively slight force, thus possessing least strength in the direction where 

 -it is most wanted. He illustrates by the following experiment, which might 

 be readily tried : " If a cylinder of lead, some four or five inches long, and 

 of about the same diameter, be cast around a cylindrical bar of iron about 

 an inch and a half in diameter, and considerably longer, the lead becomes 

 rapidly consolidated by the contact of cold material interiorly as well as ex- 

 teriorly, will have a tolerably homogeneous structure, and may be cut into, 

 beaten out, etc., without exhibiting any trace of crystallization. But if one 

 of the ends of the central bar be heated red-hot, and time be allowed for the 

 heat to be conducted along into the interior of the lead, and thence conducted 

 outward in all directions till the heat is nearly up to the melting point of 

 lead say to about 550'' Fahr. and the lead be now sharply struck with a 

 hammer, the Avhole mass will be found to have a crystalline structure, all the 

 principal axes of the long thin crystals radiating regularly from the centre ; 

 and by a few blows from the hammer the mass will separate and fall to 

 pieces, so complete are the planes of separation." 



As a consequence of this law, it is inferred that every abrupt change in 

 the form of the exterior of any casting, is attended by an equally sudden 

 change in the arrangement of the crystals, accompanied with one or more 

 planes of Aveakncss in the mass. The small cast iron cylinder of the hy- 

 draulic pi'ess used in raising the tubes of the Britannia Bridge, failed under 

 the immense pressure, until another form was substituted with a bottom 

 more rounded ; and the theory laid down, and to a certain extent established 

 by this writer, would seem to indicate that when angular forms are ab- 

 solutely required in castings exposed to great strains, it might be expedient 

 to cast the parts in rounded forms, and then turn or plane them to the forms 

 required. 



ILLUSTRATIONS OF DRAINAGE. 



Mr. Trachzel, in a recent lecture on drainage, before the London Society 

 of Arts, illustrated his remarks by means of a tin vessel, fitted with two 

 spouts. The bottom of the vessel represented what he termed the " water 

 table," or the formation which prevented the water sinking lower, and the 

 two spouts represented drains at different depths. Having filled the vessel 

 with pebbles, he poured in some water, which, descending to the bottom, 

 ran out of the lower spout or drain. Stopping the lower spout, the water 

 ran out of the upper drain. In the same manner, he said, water descended 

 through the soil as low as it could, and hence the importance of deep drain- 

 ing. Water did not by instinct run into the drains, but saturated the soil, 

 and to be carried away drains must be made at a proper depth. A three 

 feet drain would drain the land to the depth of two feet six inches only, 

 while the root of wheat required a considerably greater depth, running in 

 favorable situations to the depth of four feet, and as deep, in fact, as the 



