Review of Dana's Mineralogy. 373 



We might extract largely from this portion of the work with 

 profit to our readers, but our space confines us, and we must re- 

 fer for fuller details to the volume, now easily accessible to all. 

 Under crystallization by heat, we find the following new and im- 

 portant observations, drawn from a practical source of the highest 

 authority, and showing the importance of a close reunion between 

 the theoretical and practical arts. 



" It has been supposed that complete fusion is necessary for the for- 

 mation of crystals, or the crystallization of a mineral mass. But late 

 observations have shown, that a high temperature without fusion, or 

 even long-continued friction or vibration, will produce the same result. 

 The tempering of steel is a familiar example. The coarseness or fine- 

 ness of the grain, or, in other words, the size of the crystallizations, 

 may be varied by the temperature, or the mode of tempering, and a bar 

 that is almost impalpably fine, may in this way be changed to one con- 

 sisting of crystalline plates an eighth of an inch in breadth. In these 

 instances, the particles must have been free to move, as they are entire- 

 ly rearranged into large crystals. Mr. N. P. Ames, of Springfield, 

 Mass., who has observed numerous interesting facts bearing upon this 

 subject, informs the author that if a bar of tempered steel, bent in the 

 form of a semicircle, be heated on the inner side, when the heat has 

 reached a certain point, the bar may easily be bent around, and made to 

 curve in the opposite direction. He states that, until the moment when 

 the requisite temperature is acquired, the bar does not yield ; but at this 

 moment a change takes place, which is distinctly felt in the hands, and 

 the bar at once bends. He carefully measured the inner and outer 

 curves of the bar, after thus bending it, and found them of the same 

 length as before. This shows that there had been no compression of 

 the particles on the inner side, which would have shortened that side, 

 and therefore, also, that there was actually a removal of particles from 

 the inner to the outer side. He observes, moreover, that the elasticity 

 of the inner and outer sides was the same, which would not have been 

 the case, were the former compressed. By the old method of restor- 

 ing a warped sword-blade, it was rendered unequally elastic, and would 

 spring more easily on one side than the other ; but by the means here 

 explained, the elasticity is perfectly equal on both sides. Here, then, 

 there is a change in the position of the particles throughout the bar, 

 produced by a temperature very far short of fusion. The same exper- 

 iment was often repeated, and he found that, at every time he bent the 

 steel, the temperature required was a little above that at which it bent 

 the preceding time. 



" The change which takes place by friction or long-repeated concus- 

 sion, is probably owing to the combined action of the heat thus excited, 



