xl GENERAL SUMMARY OF SCIENTIFIC AND 



experiments the reflection of sound from flames and from 

 heated and even cold gases, and he has obtained approximate 

 measures of these reflecting powers. In the same paper he 

 also gives the first determination ever made of the mechan- 

 ical equivalent of sound. He finds that the aerial vibrations 

 produced during ten seconds by a Ut 3 fork placed in front 

 of its resonator equal in mechanical effect about 100 1 000 of a 

 Joule's unit; that is, these aerial vibrations can be expressed 

 in the equivalent work done in lifting fifty-four grains one 

 foot high. 



The most important research of Professor Mayer is his 

 discovery of a physiological law susceptible of a mathemat- 

 ical expression ; this law expresses the connection existing 

 between the pitch of a sound and the time during which its 

 sensation remains in the ear, after the vibrations causing this 

 sound have ceased outside the ear. He finds that the sound 

 of the lowest audible note of forty vibrations per second lasts 

 on the ear -^ of a second, while the highest sound, of forty 

 thousand vibrations per second, remains in the ear only the 

 5^ of a second. The treble C gives a residual sensation 

 of -3TJ- of a second. This law has shed much light on many 

 obscure facts of physiological acoustics, and in its applica- 

 tions has served to render quantitative much of the qualita- 

 tive work in Helmholtz's "Physiological Theory of Music." 



Professor Rood has devised a simple and exceedingly 

 beautiful method of determining the numbers of vibrations 

 of solid bodies, by observing in a telescope the figures pro- 

 duced by vibrations of two fine wires attached to the bodies. 

 These wires cross each other, and by superposition of their 

 motions produce figures of a similar general character to 

 those given in Lissajous' experiments with reflecting forks. 



In Thermotics we have an important research by Jannattaz, 

 in which he shows that heat is conducted in crystals and in 

 lamellar rocks better in the direction of the planes of cleav- 

 age than in directions across these planes. He has also de- 

 termined the laws for the conduction of heat in crystals, with 

 two or more planes of cleavage. 



Professor Crookes, of London, has brought out a most re- 

 markable paper on the action of heat in producing attraction 

 and repulsion between bodies placed in vacuo and in air. He 

 is bold enough to venture the suggestion that in these dis- 



