202 On the Propagation of Sound. 
The following are the velocities of sound in a second, accord- 
ing to the authorities of the names subjoined, expressed in English 
feet: 
, Roberval ..... 560 
Gassendus .... 1473 
Mersennus.... 1474 
Duhamel .. .. 1338 
Newton...... 979 from theory. 
Derham ..... 1142 
Cassini,&ec.... 1106. 
We shall not stop to examine the source of these discordant 
results, but merely observe, that the remarkable disagreement ex- 
hibited by these philosophers, in all probability, arises either from 
their not using proper pendulums vibrating seconds or aliquot 
parts of a second, but strings suspended with a plummet oscil- 
lating :—or, the distances of the stations from whence the sound 
was propagated, and observed, were either too near each other, 
or not exactly ascertained, so as to render any degree of preci- 
sion to be expected from their inquiries. 
The experiments of Dr. Derham are perhaps the most to be. 
relied upon of any that have been made in this country ; but the 
spaces through which the sound was propagated were not ri-' 
gorously verified. This objection does not apply to the labours 
of Cassini, Maraldi, &c. who made these observations in France 
about the year 1733. They observed the velocity of sound 
under a variety of circumstances,—during a diversity of winds, 
in calms, and different changes of weather,—with nearly the same 
results: besides, the distance of one station from another had been 
previously determined, with accuracy, in measuring the terrestrial 
meridian through France. The mean velocity of sound, as de- 
duced from their experiments, is 1038 Paris feet in a second ; 
and if the length of the French foot be to the length of the 
English foot as 1°06575 to 1, as stated by General Roy, the 
distance will be equal to 1106 English feet; and it is highly pro- 
bable, that this determination is more to be relied upon than any 
other experiments which have hitherto been made. > 
It may not be improper here to mention the excellent oppor- 
tunity afforded us in this country, of settling this pomt in the 
most satisfactory manner. I allude to the many favourable situ- 
ations which present themselves, whose distances from each other 
have been most accurately measured during the grand Trigono- 
metrical Survey of England by Lieut.-col. Mudge, &c. 
The theoretical principles of the propagation of sound, ad- 
vanced by Sir Isaac Newton in the 47th proposition of his Ma- 
thematical Principles of Natural Philosophy, are simple, elegant, 
and appear consonant to the visible operations of nature, so far 
as 
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