104 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



apparatus. Any increase of length in the bar Avill rotate 

 the axis and the mirror, and so may be observed and com- 

 puted in the usual way. The bar to be measured is sur- 

 rounded by a tank with glass sides, which may be filled 

 with liquids at different temperatures. The price of the 

 apparatus is only fifty marks. 



Maskelyne has called attention to the similarity between 

 the pitted surface of meteorites and that of the unburned 

 fragments of coarse-grained gunpowder which fall at some 

 distance from the muzzle of a large piece of ordnance. lie 

 expresses the opinion that the "pitting" is due to the sort 

 of splintering effect of enormous heat suddenly applied, which 

 results from the difference in the mechanical facility with 

 which the sudden heat penetrates the mass at different 

 points on its surface, melting out and dissipating in the air 

 the material at those points, partly as a consequence of 

 greater conductivity and partly of great fusibility. 



Hartley has presented to the Royal Society a paper on the 

 constant vibration of the minute bubbles which are found 

 frequently in mineral cavities. In one case a cavity in 

 quartz became two thirds filled with liquid at 3.5 C, the 

 gas bubble occupying the remaining space, and having a 

 trembling motion. As the cooling went on, the bubble de- 

 creased in size, and the motion became more and more rapid, 

 until it finally moved across the cavity. He attributes the 

 motion to the thermal changes which are taking place even 

 within the crvstal itself. 



3. Change of State. 



Gernez has studied the conditions under which the pris- 

 matic and the octahedral forms of sulphur are produced, and 

 finds that when liquid and in the condition of surfusion at a 

 temperature below 113 C, octahedral crystals are developed 

 by a fragment of a crystal of this form, while prismatic crys- 

 tals may be grown from the same surfused mass by contact 

 of a piece of prismatic sulphur. 



Beckerhinn has confirmed the conclusion long ago reached 

 by practical experience by Mowbray, that congealed crystal- 

 lized nitroglycerin is far less sensitive to shocks and blows 

 than the liquid substance. lie used in his experiments a fall- 

 machine having a block of wrought iron of 2.13 kilograms 



C7 CJ <U 



