C. GENERAL PHYSICS. 125 



C. GENERAL PHYSICS. 



THE RESISTANCE OF GLASS TUBES TO RUPTURE. 



M. Cailletet finds that a tube stands pressure from the out- 

 side better than the inside ; but the pressures that a tube can 

 bear from the inside are very great. A glass tube of nine 

 millimeters internal diameter and one millimeter thick was 

 submitted to an outside pressure of 460 atmospheres, without 

 injury, and subsequently to an internal pressure of 104 at- 

 mospheres, when it burst. 12 A, IX., 316. 



THE RELATIONSHIP BETWEEN ELECTRICITY, HEAT, AND MOLEC- 

 ULAR FORCES. 



Professor Barrett, of Dublin, calls attention to certain re- 

 markable molecular changes occurring in iron wire at a low 

 red heat. Mr. Gore, in 1869, published the important fact 

 that, when iron wire is heated to bright incandescence, and 

 then allowed to cool, a momentary elongation occurs just 

 after it has begun to contract by cooling. Mr. Barrett hav- 

 ing undertaken further to investigate this subject, finds that 

 during the preliminary heating of the wire a slight and mo- 

 mentary retrogression in the otherwise regular expansion 

 ay as noticed at a temperature corresponding to the powerful 

 jerk that occurred on cooling ; and, again, it w T as evident 

 that the anomalous deportment of the iron occurred approxi- 

 mately at the same temperature at which iron undergoes 

 magnetic change. All kinds of iron do not exhibit this be- 

 havior, some showing it in a more or less marked degree. 

 Barrett was not able to detect any change in heating or cool- 

 ing in certain specimens of good, soft iron wire, but in hard 

 iron wire, and notably in steel w T ire, it is very apparent. 

 Zon., Z(7., and Dub. Philos. Mag., 1873, 472. 



THE FIRST REPORT OF THE BRITISH ASSOCIATION COMMITTEE 

 ON DYNAMICAL AND ELECTRICAL UNITS. 



The first report of this committee was made at the recent 

 meeting of the British Association for the Advancement of 

 Science, and is confined principally to the selection and no- 



