PHYSICS. 211 



alkaline, the pedetic power is lessened, but the water acts on 

 oleaginous matter. But if soap be also added, Ave have the 

 advantage of both the alkali dissolving power and of the pe- 

 detic cleansing power. 



A paper has been published by Van der Mensbrugghe on 

 the cause of the apparently spontaneous movements of bub- 

 bles of air in levels, and of bubbles of vapor in the micro- 

 scopic cavities of minerals. These motions are explained by 

 changes of tension in the surface of the liquid produced by 

 changes of temperature, this tension always decreasing at the 

 warmer end, and the bubble consequently moving towards 

 this end. But now, as a thin film of water remains on the 

 glass at this point, the surface of the liquid is increased there, 

 thus lowering the temperature and increasing the tension; 

 so that, when the temperature ceases to rise, the bubble goes 

 back again. In the case of microscopic cavities, where the 

 bubble is formed of the vapor of the liquid, the movement is 

 yet more rapid, changes of temperature producing evapora- 

 tion or condensation, by which the dimensions, and hence the 

 tension, of the surface are altered. The author thinks the well- 

 known Brownian movements thus explicable. 



Thompson has communicated a ^aper to the London Phys- 

 ical Society upon permanent Plateau films, an abstract of 

 which is given in Nature. The best films are obtained by 

 using a mixture of 46 per cent, of pure amber-colored resin 

 and 54 of Canada balsam, which should be heated to from 

 93 to 95 C. The frames for forming: the films are made 

 of brass wire 0.3 mm. in diameter, and when thicker wire 

 is employed they are found to be irregular, in consequence 

 of the retention of heat by the metal. The films are ob- 

 tained by simply introducing these frames into the heated 

 mixture, and they harden almost immediately on exposure 

 to the air. But better results are obtained by slow drying 

 in an air-bath heated up to 80 C.,and allowed to cool. In 

 proof of the toughness of the films, it was mentioned that a 

 fiat circular film four centimeters in diameter had supported 

 a 50-gram brass weight at its centre. 



Duclaux has studied quite extensively the phenomena of 

 surface tension exhibited by the alcohols and the acids of the 

 fatty series. The alcohols employed were methyl, ethyl, 

 isopropyl, isobutyl, amy], and capryl alcohols; and the acids 



K 



