PHYSICS. 339 



Crystalline salts weld with remarkable facility, giving compact, trans- 

 parent masses. Coal at 0,000 atmospheres forms a solid brilliant block, 

 easily molded. Wax at 700 atmospheres liows like water. ParafQn 

 requires 2,000 atmospheres. Gum arable is plastic at 5,000 atmospheres, 

 and sealing-wax shows this e£fect still more markedly. [Ann. Chim. 

 Phys., February, 1881, V, xxii, 170.) 



2. Of liquids. 



Bjerknes exhibited at the Paris Electrical Exhibition an ingenious 

 set of apparatus for showing the fundamental phenomena of electricity 

 and magnetism by the analogous ones of hydrodynamics. The fact that 

 a vibrating body attracts light objects near it has long been known, 

 and the explanation that the air is rarefied by the agitation, the press- 

 ure is greater at a distance, and the light stationary body is pressed 

 toward the vibrating one, was given in 1867 by Sir William Thomson. 

 By means of two small pumps pulses of compression or rarefaction may 

 be produced in drums or spheres of elastic material immersed in water, 

 or these maybe caused themselves to vibrate. If two drums are used, 

 and both contract and expand together, there is attraction, while if one 

 contracts and the other expands there is repulsion. But if two spheres 

 be made to oscillate so that they move in the same direction at the 

 same time, then there is repulsion between them. If they move in 

 opposite directions there is attraction. The author considers the water 

 in his trough as the analogue of Faraday's medium, and the results 

 which he has obtained with his apparatus are very striking. {J. Phys., 

 December, 1881, x, 509; Nature, August 18, 1881, xxiv, 360.) 



Volkmann has pointed out that in the determination of the specific 

 gravity of heavy liquids, as mercury, by means of the pycnometer, an 

 error is introduced by the deformation of the bottle by the pressure 

 within. In the case of a bottle provided with a capillary tube divided 

 equally, he found that on filling it with mercury the toj) of the column 

 stood at 68.1 divisions when the whole was immersed in mercury to the 

 same level ; but on removing it the column fell to 65.4. Taking the 

 precaution to eliminate this source of error, a new determination of the 

 value of the density of mercury gave the number 13.5953zt .0001. [Na- 

 ture, July 28, 1881, xxiv, 294.) 



Plateau has communicated to the Belgian Academy some interesting 

 experiments with liquid films. A piece of fine iron wire is bent so as 

 to represent in outline a sixpctaled flower; it is then dipped for a mo- 

 ment in nitric acid and washed, and then dipped in glyceric solution 

 and idaced under a bell-jar, and near a window. A pretty play of bright 

 colors is observed, which continues for hours. To prove the contraction 

 of such a film when it breaks, a bubble 11 centimeters in diameter is 

 blown with glyceric liquid b^' tobacco smoke and placed on a ring. If 



