PHYSICS. 581 



ters, and the like, and lias given a description of the apparatus used. 

 {Jour. Phys., October, 1883, II, n, 4G3.) 



Various modifications in the mercury air-pump have been suggested. 

 Among these is that of Karavodine, who modifies Topler's form of pump 

 by causing the upper reservoir to open into the discharge pipe by a 

 straight instead of a recurved tube. He has also added a valve iu the 

 exhaust tube to preveut the mercury from passing into the desiccator or 

 into the vessel to be exhausted. A double-acting mercury pump has 

 been devised by Serravalle. Two similar vessels, containing mercury 

 and connected by a long caoutchouc tube, are raised and lowered alter- 

 nately with each other on opposite sides of a vertical support. Each 

 vessel has a three-way cock at its top; one opening in a certain position 

 conducts off the excess of mercury, while a second communicates through 

 a rubber tube with a spherical piece fixed laterally near the middle of 

 the vertical support. This spherical piece has three communicating 

 ports, two of them opposite leading into the mercury vessels; the third 

 is connected to the vessel to be exhausted. The three-way cocks at the 

 tops of the vessels are mechanically turned at the upper and lower ends 

 of their course by means of a toothed sector and rack iu the one case 

 and a pin and projecting piece iu the other. (Jour. Phys., December, 

 1883, II, II, 558; Nature, February, 1883, xxvn, 324.) 



ACOUSTICS. 



Auerbach has experimented to determine the influence exerted by 

 liquids upon the pitch of the sound given by the cylindrical glass ves- 

 sels in winch they are contained. The number of vibrations was deter- 

 mined on a mouochord. In the first experiments, which were made with 

 water, there was always a lowering of the sound produced. ' He calls 

 geometric fall the ratio of the number of vibrations given by the empty 

 vase to the number given when it is full, and arithmetric fall the ratio 

 of the difference of these two numbers of vibrations to that of the 

 empty vase. He finds that the former of these values, in the case of a 

 vessel filled with liquid, is as much smaller as the sound is more acute, 

 is sensibly independent of the height of the vessel, and is inversely as 

 the diameter of the vessel. The latter varies inversely as the square 

 root of the number of vibrations given by the empty vessel and as the 

 square root of the diameter of the vessel. Relative to the wave-length 

 of the sound given by the empty vessel, the arithmetric fall depends 

 only on the number of wave-lengths contained in the radius of the cyl- 

 inder, and is inversely proportional to the square root of this number. 

 The fall of pitch depends also on the height of the liquid when the ves- 

 sel is not full, but is not proportional to it. To produce a pitch one-half 

 less than that given by the full vessel the column of liquid must be from 

 two-thirds to three-fourths of the total height. For other liquids than 

 water Auerbach finds that the specific fall of pitch increases with the 



