PHYSICS. 341 



Bunseu pump has originated ; erroneously as it appears to Sprengel 

 bimsell^ {Nature, May I'J, 1881, xxiv, 53.) 



Rood has continued his investigations on the mercury pump, and has 

 further perfected it, so that he has now obtained vacua of -ir§-oiroooxro 

 of an atmosphere. The form of pump used is Sprengel's, with consider- 

 able modification in its details, not intelligible without the figures which 

 accompany the pajjer. The v acua were measured with the McLeod 

 gauge, specially modified for the purpose. The greatest care was taken 

 in annealing all the glass, and during action the pump was warmed with 

 a Bunsen burner. The leakage was so small that in a year it would 

 amount to only 2.877 cubic millimeters under the normal air pressure 

 {Am. J. Set., August, 1881, iii, 90.) 



Angot has described a new and simple registering barometer, con- 

 structed by Eichard freres. Six or eight holosteric barometer-boxes, 

 so attached that their changes are added, serve to measure the varying 

 air pressure. The npper box acts on the short arm of a lever, the long 

 arm of which inakes the record on a revolving cylinder. The arms of 

 the lever are adjusted so that the motion of the end of the longer cor- 

 responds exactly to the variation of the mercurial barometer. On the 

 cylinder is a sheet of paper properly divided. The rotation is effected 

 by clock-work, so that the cylinder revolves once in seven days. A i^en 

 containing glycerin ink, being attached to the lever-arm, inscribes the 

 curve on the paper. A metallic thermometer, recording similarly, has 

 also been constructed, and a hygrometer is projected. {J. Phi/s., August, 

 1881, X, 3G3.) 



ACOUSTICS. 



Cross has observed that under certain circumstances sound is emitted 

 from a Crookes tube in action. Using the tube in which a piece of liluti- 

 num is heated by the impact of the molecules shot out from the con- 

 cave negative pole, a clear and quite musical note was heard. It was 

 at first supposed to be due to the circuit-breaker j but it did not coin- 

 cide with this in pitch, and changes in the rapidity of vibration of the 

 latter did not affect the note. The effect seemed to be produced by 

 the vibration of the sheet platinum in its own period under the influ- 

 ence 6f the molecular blows. The sound resembled somewhat the i)at- 

 tering of rain against a window-pane, but it was higher in pitch and 

 more musical. The reversing of the current changed entirely its char- 

 acter. The sound was heard also in the mean free-path tube, best 

 when the middh^ plate was positive, and in a tube containing calcium 

 sulphide lor i)hosphorescence. {Proc. Am. Acad., Xovember, 1881; 

 Nature, May 12, 1881, xxiv, 45.) 



Cook has proposed the name sonorescence for the phenomena of the 

 conversion of intermittent light into sound, discovered by Graham 

 Bell. Obviously this was suggested by the analogy of the word with 

 fluorescence, given by Stokes to the change of ultra-violet ravs into 



