OP ARTS AND SCIENCES, 497 



SO well known to plumbers and workers in alloys. We here refer 

 only to the conditions of the plessite ; but at times we also find 

 the whole meteoric mass divided up by small cracks, and thus ren- 

 dered so friable that it can readily be broken into coarse polygonal 

 grains with a hammer. Such a disintegration must have been a me- 

 chanical one, affecting the whole mass subsequent to its solidification. 

 It is similar to the well-known effects produced on iron by long- 

 continued jarring, and may have been the result of the violent con- 

 cussions which aie known to be caused by the passage of the meteorite 

 through the air. We have recently had the opportunity of examining 

 a specimen of aluminum bronze sent to the Laboratory of Harvard 

 College by Prof. C. F. Mabery of Cleveland, Ohio, which most strik- 

 ingly illustrates the effect hei-e described. The bronze, consisting 

 of 90% copper and 10<^ aluminum, had been cast into a bar and re- 

 heated for forging. When the heated bar was laid on an anvil and 

 struck with a hammer, it broke up into small polygonal grains, just 

 like those of the Cosby's Creek and Seelasgen meteorites. 



Such products as have been described all point to a very slow 

 cooling of the molten metal out of which the crystals came, and this 

 is the opinion held by the best observers in regard to this process. 

 Thus Mr. Sorby writes : " These facts clearly indicate that the Wid- 

 manstatt's figuring is the result of such a complete separation of the 

 constituents, and perfect crystallization, as can occur only when the 

 process takes place slowly and gradually. They appear to me to 

 show that meteoric iron was kept for a long time at a heat just below 

 the point of fusion, and that we should be by no means justified in 

 concluding that it was not previously melted. Similar principles are 

 applicable in the case of the iron masses found in Disco ; and it by 

 no means follows that they are meteoric, because they show the Wid- 

 manstiitt's figuring. Difference in the rate of cooling would serve 

 very well to explain the difference in the structure of some meteoric 

 irons, which do not differ in chemical composition ; but as far as the 

 general structure is concerned, I think that we are quite at liberty to 

 conclude that all may have been melted, if this will better explain 

 other phenomena." * Similar opinions have been expressed by 

 Tschermak and Haidinger. 



We have tried in this paper to establish the following points : — 

 First. That many of the masses of meteoric iron in our collec- 



* Nature, 1877, vol. xv. p. 498. 



VOL. XIII. (n. 8. XXI.) 32 



