808 



SCIENCE. 



[N. S. Vol. IX. No 232. 



been transmitted to the Secretaries of the 

 Royal Society, with an occasional expres- 

 sion of opinion as to the merits of the views 

 presented in the several reports. 



The next step will be the consideration 

 of these reports and of similar reports 

 from other countries and the formulation 

 of a definite plan by the Provisional Inter- 

 national Committee. 



In view of the failure of Congress to make 

 an appropriation for carrying on the work 

 in this country, it will be necessary should 

 the Catalogue begin January 1, 1900, to 

 make some special provision. It is hoped 

 that, by the cooperation of universities and 

 libraries in five or six of the large centers, 

 the work can be carried on for one year, and 

 that when the subject is next presented to 

 Congress it will meet with more favorable 

 consideration. 



Cykus Abler. 



Smithsonian Institution. 



A DOUBLE mSTEUMENT AND A DOUBLE 

 3IETH0D EOS THE MEASUBE- 

 MENT OF SOUND. 

 The work briefly sketched here, at the 

 request of the editor of Science, was done 

 by the writer in the laboratory of Clark 

 University, and grew out of the suggestion 

 of Professor Webster, that the optical ar- 

 rangement of Michelson's refractometer, 

 combined with an accoustical method em- 

 ployed by Wien,* might yield a sound- 

 measuring ajiparatus of great sensitiveness. 



RECEIVER. 



For this purpose one totally reflecting 

 mirror of the refractometer was made very 

 small and light, and was mounted upon a 

 thin glass plate, which formed a portion of 

 the walls of a spherical, Helmholtz reson- 

 ator. A pure tone of the same pitch as 

 the resonator causes the interference bands 

 to vibrate with the same frequency. In 

 order to render the maximum displacement 



* Wied. Ann., 1889, p. 835. 



visible, the fringes were made vertical, then 

 cut down to a narrow band by a screen with 

 a horizontal slit. This band was viewed by 

 means of a telescope whose object glass was a 

 small lens mounted upon the end of a tun- 

 ing fork of the same frequency as the 

 source of sou^nd. The fork was driven 

 electrically and the motion of the lens was 

 perpendicular to the narrow band, so that, if 

 the sensitive resonator plate were protected 

 from all sound, the fringes would not be 

 displaced, but the motion of the object glass 

 would stretch out the narrow band into a 

 broad band of vertical fringes. If now a 

 tone were admitted to the resonator the 

 fringes would be simultaneously displaced. 

 In case of the identical agreement of both 

 frequency and phase of the telescope fork 

 with the forced vibration of the resonator 

 plate (excited by the source of sound) the 

 composition of motions would result in 

 a similar band, but one covered with ob- 

 lique fringes whose slope is a function of 

 the intensity of the sound. Identitj^ of 

 phase is easily realized by making the tele- 

 scope fork actuate the source of sound ; 

 but identity of phase depends upon the dis- 

 tance of the source of sound (as well as 

 upon some elements involved in the me- 

 chanical construction of the source of sound, 

 which elements cannot be varied within 

 limits sufiiciently wide to compensate for 

 all phase differences depending on various 

 distances of the source), and consequently 

 this identity could be obtained only at par- 

 ticular settings. In a room filled with 

 standing waves from the source, these set- 

 tings can be found by moving in the three 

 dimensions either the source of sound or 

 receiver. But this adjustment is laborious, 

 and this limitation renders the apparatus 

 unsuited to general investigation. Without 

 such adjustment the composition of the 

 motions of the bright spots in the narrow 

 band gives a set of overlapping ellipses, ob- 

 scuring the displacement. 



