TRANSACTIONS OF THE SECTIONS. 
559 
and also to those of plates formed of substances possessing 
unequal elasticities in different directions. He concluded by 
showing the possibility of constructing an optical instrument 
which should exhibit exact resemblances of all the component 
and resultant figures of vibrating surfaces, and, at the same 
time, serve as a calculating machine for these phasnomena, by 
performing ail the requisite synthetical operations. 
On the Velocity of Sound. By John Herapath. 
The author, referring to the methods employed by Newton 
and others for determining, from theory alone, the velocity of 
sound, took occasion to compare the fundamental postulate 
usually employed in this investigation, viz. the limited mutual 
repulsion of aeriform particles, with his own views of the consti¬ 
tution of gaseous bodies, formerly published at length in the 
Annals of Philosophy for 1821 ; according to which, the mecha¬ 
nical properties of aeriform bodies depend upon the internal 
motions of their hard particles. In the present communication, 
the author, upon the supposition of a particular system of in¬ 
ternal motions, deduced formulas for the calculation of the 
velocity of sound, the results of which, at different tempera¬ 
tures, he compared with the best experiments on the subject 
in common air. Passing, then, to the consideration of the 
intensities of sound in different airs, he deduced the relation 
between these intensities and the corresponding velocities, and 
compared the results of his hypothesis with the tones produced 
by various gases, as given by M. Dulong, Annales de Chimie, 
tom. xli. p. 150. 
4. MAGNETISM.—ELECTRICITY. 
Experiments on the Intensity of Terrestrial Magnetism , at 
Liverpool and Manchester, with Hansteen s Needles. By 
W. S. Traill, M.D. fyc. Performed at the request of the 
Association. 
The needles employed by Dr. Traill were furnished to him, at 
the request of the Association, by the Royal Society of Edin¬ 
burgh. The following are the results. 
Botanic Garden , Liverpool. 
Experiments with the cylindrical needle, No. 1, corrected 
for temperature, &c. 
March 27, 1832 ;—300 vibrations in 797*70 
April 2,--- 797*64 
- 19,. ... —~ 797*76 
