584 SCIENTIFIC RECORD FOR 1883. 



mirror oscillates about the wire as a diameter. By means of a rubber 

 tube the interior of the paraboloid is put in communication with any 

 sounding mass of air, and the vibration of the mirror causes a beam of 

 sunlight reflected from it to describe a line on the screen, which may 

 be drawn out into curves by a second mirror vibrating* perpendicularly. 

 (J. Phys., December, 1883, II, n, 553.) 



Michelson has described a method of ascertaining with any desired 

 accuracy the late of a tuning-fork. The method consists, first, in de- 

 termining the rate in terms of an electrically vibrated fork, aud, second, 

 in fixing the absolute rate of this second fork. The electric fork carries 

 a mirror on one prong, in which the reflection of a Geissler tube is seen 

 when illuminated once a second by means of a pendulum. If the fork 

 makes an exact number of vibrations per second the illumination of the 

 tube, finding the fork always in the same place, will appear always in 

 the same position. But if the fork makes more or less than this by any 

 fraction, the position of the flash will successively change, passing 

 through all its phases in one complete period. If a flashes take place 



in oue period in the case of an Ut 2 fork, it makes obviously 128 ± — 



vibrations per second. By using the fork to be rated with a microscope, 

 with cross-hairs focused on one edge of the fork, the Geissler tube being 

 behind it, the use of an electrical fork may be dispensed with. (Am. J. 

 Sci., January, 1883, III, xxv, 61 ; PHI. Mag., February, 1883, V, xv, 84.) 



The attention of the Berlin Physical Society has been called by 

 Christiani to certain peculiarities observed with Koenig tuning-forks 

 injured by the fire in the Physiological Institute. When the rust had 

 been removed, and new resonance boxes provided, one of the Mi 3 forks 

 showed, after tuning and sounding, a maximum of tone when one side 

 of it was turned toward the closed end of the case. Another Mi 3 

 fork, though in unison with the first, did not present the phenomenon, 

 though when the cases were exchanged it appeared, showing that the 

 new case produced the effect. Another experiment was made to show 

 total absorption of tone. A singing flame tuned approximately to Mi 3 

 was unaffected when the resonance case bearing the Mi 3 fork was held 

 near it with its open end horizontal. When, however, the same case 

 without its fork was brought to the same position the sound immediately 

 ceased. (Nature, January, 1883, xxvn, 236.) 



Francis Galton has improved the whistles which he contrived in 1876 

 for testing the upper limits of the power of hearing very shrill notes 

 by different men and animals, by using hydrogen in place of air to pro 

 duce the sound. Since this gas is about thirteen times as light as air, 

 the number of vibrations per second would thus be increased nearly 

 four times. The whistles were made with a movable piston, by which 

 the pitch could be varied; but since to give its proper note the depth of 

 the cylinder should be 1.5 times its diameter, it follows that the diameter 

 of a whistle giving 24,000 vibrations, and whose depth is only 0.14 inch, 



