INDUSTRIAL PROGRESS DURING THE YEAR 187G. U 



the author concludes, first, that the vibrations of a fork are not ab- 

 soUitely isochronous, the duration of its period varying with the am- 

 plitude and the temperature ; second, that consequently any chro- 

 nographic instrument can give comparable results at ditferent times 

 only if the temperature and the amplitude remain the same ; and, 

 third, that if the amplitude does not exceed three or four millime- 

 ters, and if the temperature varies but slightly, the number of peri- 

 ods per second may be exact to 0.0001 nearly. 



Mayer has given in Nature some notes of remarkable exjjeriments 

 in acoustics on the obliteration of one sound bv another. He finds 

 that the ticking of a clock, for example, completely obliterates the 

 ticking of a watch at the periods of coincidence, the intensity of the 

 clock ticks which effect this obliteration being three times that of 

 the watch ticks. Moreover, he observes that a sound can not oblit- 

 erate another lower in pitch than itself a result of great physiolog- 

 ical significance. These fiicts the author applies to orchestral 

 music, and shows that this obliteration of higher by lower sounds 

 should and does seriously mar the intended effect of the music, and 

 hence that the study of its conditions is necessary in musical com- 

 position. 



The same physicist has published a preliminary note on two new 

 methods of research in acoustics, in which he asks the privilege of 

 being permitted to develop them. The first is a plan for the deter- 

 mination of the relative intensities of sounds of the same pitch. 

 This is effected by placing a loose membrane any wdiere between 

 the centres of origin of tw^o sounds of the same pitch, and perjjen- 

 dicular to the line joining them, and then by any device determin- 

 ing the position where the membrane ceases to vibrate. The instru- 

 ment he calls a phonometer. The second is a method for deter- 

 mining the direction of sounds. It consists of a membrane capable 

 of being moved in any azimuth, and which can therefore be placed 

 at right angles to a sonorous w^ave front. When it reaches this po- 

 sition it can not vibrate, since the impulses are alike on the two 

 sides. To increase the aural parallax, two resonators may be used at 

 the ends of a horizontal rod. 



Dvorak has studied certain attractions and repulsions observed in 

 the vicinity of sonorous bodies when they are vibrating. If, for ex- 

 ample, a rod of wood be made to vibrate slowly, and a small square 

 of paper suspended by a silk filament be moved slowdy around it, 

 the surface of the paper being preserved vertical, it will be noticed 

 tliat in certain positions there will be attraction, and in certain oth- 

 ers repulsion of the paper. The author attributes these movements 

 to currents of air generated by the vibrating mass, and proves his 

 theory by a number of highly interesting experiments. 



Miiller has experimented to determine the pitch of the notes given 

 by transversely vibrating rods of gypsum when dry and when 



