C. GENERAL PHYSICS. 169 



Dr. Nessen, made with an apparatus of considerable delicacy, 

 lead to results somewhat different from those of Kohlrausch. 

 He finds the strings observed to be highly susceptible to the 

 least radiation of warmth ; but, avoiding this source of er- 

 ror a he concludes that the elastic reaction in the case of tor- 

 sion follow r s the law expressed by a simple exponential curve. 

 The magnitude of the reaction increases with the diminution 

 of temperature, as also with increasing angle of torsion, and 

 with increasinc? duration of time. The co-efficient of elastic 

 reaction increases with increasing temperature only, being 

 independent of the extent of the duration of the torsion. 

 MonatsbericJtt K. P. Akad. Wiss., Berlin, February, 1874, 141. 



THE EVAPORATION OF LIQUIDS. 



Stefan has endeavored to reduce to some definite laws the 

 phenomena of the evaporation of liquids (especially the dif- 

 fusion of vapors), and has made a series of experiments, prin- 

 cipally on the evaporation of ether. He finds that in nar- 

 row open tubes the velocity of the evaporation is inversely 

 proportional to the distance of the surface of the liquid from 

 the open end of the tube. It is independent of the diameter 

 of the tube, and increases with the temperature, so far as the 

 vapor pressure increases with the temperature. If the press- 

 ure of the vapor becomes equal to that of the air, the formu- 

 la given by Stefan shows that the liquid then boils. If the 

 evaporation takes place in closed tubes, bubbles form and 

 issue, continually, at such a rate that the times in which equal 

 numbers of bubbles form are proportional to the numbers 3, 

 5, 7, etc. If the tube contains hydrogen instead of air, the 

 bubbles form in one fourth of the time ; or, in other words, 

 evaporation proceeds four times as rapidly in hydrogen as in 

 air. 4 D, 1874, VII., 142. 



THE DISAGGREGATION OF TIN BY CONCUSSIONS. 



One of our former contemporaries records as a great rarity 

 a curious case of the disaggregation (or disintegration) of 

 metallic tin. The facts of the case are as follows: A com- 

 mercial house at Rotterdam had dispatched a quantity of 

 tin in form of pigs, by railway, during a hard frost. It ar- 

 rived at its destination as a powder composed of large crys- 

 talline grains. Its appearance was so unlike that of tin of 



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