340 PHYSICS. 



the top be broken wheu it becomes blue the mass of smoke is shot ver- 

 tically upward and then spreads out horizontally. {N'ature, October 20, 

 1881, xxiv, 593.) 



Oberbeck has experimented to ascertain the truth of the distinction 

 made by Plateau between the surface viscosity and the internal vis- 

 cosity of liquids. He finds that with distilled water the resistance in- 

 creases suddenly, and to quite considerable extent, whenever the uj^per 

 edge of the plate comes into the free surface, and ho does not doubt 

 that this is due to increased friction in the surface layer. In pure water 

 this increase of resistance was C0.9 per cent., and in salt solutions from 

 54.1 to 75.1 per cent. In alcohol there was a decrease of 11.9, in oil of 

 turpentine 12.6, and carbon disulphide of 2G.3 per cent. ( Wiedemami's 

 Annalen, 1880, II, xi, 034.) 



De Eomilly has contrived a very effective form of centrifugal pump, 

 by which, even by hand, water may be raised to a height of 150 meters. 

 Several forms of it are figured in his paper, and an ingenious applica- 

 tion of the same principle is made use of to keep the pivots oiled. {J. 

 Phys., July, 1881, x, 303.) 



3. Of gases. 



Crookes has presented a paper to theEoyal Society on the viscosity 

 of gases at high exhaustions. Maxwell had come to the theoretical 

 conclusion, in 1859, that the coefficient of friction or the viscosity of a 

 gas should be indei^endent of its density ; and this conclusion he sub- 

 sequently found to be true experimentally for pressures between 30 

 inches and 0.5 inch, the coeflBcient of friction in air being practically 

 constant. Crookes has sought to extend these experiments by testing 

 the question at much higher exhaustions than had before been used. 

 His apparatus consisted of a globe with a long neck within which was 

 a light i^late of mica suspended by a fine fiber of glass. By means of 

 a mirror on the fiber the oscillations of the plate could be read with the 

 usual lamp-stand and scale. He finds that the logarithmic decrement 

 of the oscillation is sensibly the same until the pressure reaches 3 milli- 

 meters, when there is a rapid and marked change in its value, continu- 

 ing to the highest exhaustion obtained, 0.02 M, or one fifty millionth of 

 an atmosphere. The author regards this as additional jiroof of the 

 existence of the fourth or ultra-gaseous state of matter. {Phil. Trans., 

 February, 1881, Part II, p. 387.) 



Sprengel has pointed out the fact that in his paper published in the 

 Journal of the Chemical Society in January, 1865, he distinctly de- 

 scribed the Avater-air pump. He sent a copy of this paper to Bunsen, 

 who, three years later, printed his paper on the washing of precipitates, 

 in which the water-pump was described. He alludes to the matter 

 thus : " I employ a water-air pump constructed of glass on the princi- 

 ple of Sprengel's mercury-air pump." From this statement the name 



