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11. Some Experiments and Ohfervations concern" 
ing Sounds, By Mr. Walker, late of Brazen- 
Nofe- College ^ Oxon. Communicated by 
Dr. W. Mufgrave^ FelhCoU. Phyf. andK,S. 
INtending to try the Swiftnefs of Sounds, I provided 
a Pendulum which had Two Vibrations in i" of 
Time this I carefully adjufted at aWatch-maker's ; it was 
a Piece of finall Virginal Wire with a Piftol Bullet at the 
end of it , the Length of it was 9 j% Inches to the middle 
of the Bullet : I firft made it about of an Inch longer, 
viz. i of the length of a Pendulum that vibrates z^/, 
^ but found it too flow, which I expeded, becaufe Mer- 
femus tells us, {Harm, Vniv. l. z. pro. 26.] that Two 
Pendulums had sheir Vibrations one twice as quick as the 
other, whereas one was % Foot, the other 8 1 Foot con- 
' trary to what GaliUo demonftrates would happen if the 
Air did not hinder ; who proves that Pendulums of dif- 
ferent lengths [would in Vacuo] have the times of their 
Vibrations in fub-duplicate Proportion to their lengths. 
I took this Pendulum, and ftanding over againft a 
high Wall I clapt Two fmall pieces of Boards together, 
and obferved how long it Was e're the Echo return'd, and 
I removed my Station till I found the Place whither the 
Echo retyrn'd in about half a Second. But that I might di- 
ftinguifli the time nqore nicely, I clapt every Second of 
Time Ten or Fifteen times together fb that by this 
Means I could the better difcover whether the Diftances 
betwixt the Claps and the Echoes, and the following 
Claps were equal. And though it be very difficult to be 
exaft, yet 1 could come within fome few Yards of the 
Place I fought for, thus : I obferved the Two Places 
where I could but juft difcover that I was too near, and 
T 1 1 where 
