48 ROYAL SOCIETY OF CANADA 
graphic images in order to determine the successive positions at dif- 
ferent times of the planet Venus in its passage across the sun. It was 
Janssen also who, in 1876, first suggested the idea of applying succes- 
sive photograms to the study of animal locomotion. The analysing 
of such movements was first accomplished by Muybridge of San 
Francisco. The method has been largely extended and perfected by 
M. Marey, who has employed it in studying the locomotion of all sorts 
of subjects, from men to insects. 
Electric Transmission.—The electric transmission of sound was first 
accomplished by Philipp Reis in 1864. The discovery, however, not 
having been properly announced to the scientific world, did not receive 
the attention it deserved. Had it been published by Poggendorff, to 
whom it is said a preliminary note on the subject was sent, Graham 
Bell’s invention of the telephone (1876) would probably have been 
reached at an earlier date. 
The Wave-Siren Method.—The last of the methods to be noticed is 
that employed by Rudolph Kænig in his Wave-siren. In this instrument 
a metal band or dise with curvilineal edges passes before a narrow slit 
from which issues a current of compressed air. By means of these 
discs we can produce either simple sounds, or sounds of various 
timbres, containing such harmonics as we please, the intensities and 
phases of the latter being varied at will. The first wave-siren was 
constructed in 1867, and the account of the first series of experiments 
was published in 1881. 
The mere enumeration of the methods of acoustical research which 
have been devised since the days of Chladni is an indication of the 
enormous advances which have been made in this branch of science. 
It remains now to state more particularly what these additions to our 
knowledge of acoustical phenomena have been. This can be most 
conveniently done under the following heads, viz:—the velocity and 
diffraction of sound; its pitch, intensity and timbre; and the phenomena 
produced by the coexistence of two or more sounds. 
The Velocity of Sound.—Long before the beginning of the last 
century it had been observed that the propagation of sound was not 
instantaneous. Mersenne in fact had tried to estimate the velocity by 
experiments on echoes, and by counting the time which elapses between 
the flash of a gun and the report. The latter experiments were also 
repeated by Kircher as well as by the Academy of Florence in 1660. 
The same experiments were subsequently, in 1738, undertaken by 
members of the Academy of Sciences at Paris; by savants, such as 
Kestner, Benzenberg, Goldingham, and by others; but the results 
obtained did not gain the confidence of the scientific world. A new 
series of experiments was accordingly undertaken in 1822, on the sug- 
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