118 W. W. Sacques— Velocity of very Loud Sounds. 
70, 90 and 110 feet from the mouth of the cannon, were placed 
e membranes, elevated about three feet above the ground. 
These membranes consisted each of a hoop nine inches in 
diameter over which was stretched a sheet of thin rubber. To 
the center of the membrane, and on the side toward the can- 
non, was attached a very small shelf of polished brass. U 
this rested one end of a delicate steel spring, the other end being 
fixed to an independent support. 
e wire that brought the current of electricity from the 
chronograph house was connected with the spring, and from the 
helf a second wire returned to the chronograph. When the 
spring rested upon the shelf the circuit was closed. The pass- 
sound wave, however, would move the membrane 
and break the circuit, causing a register on the chronograph. 
When the spring fell it rested upon a contact point from which 
a wire ran to the next membrane of the series, so that the cir- 
cuit, immediately after being broken at the first membrane, was 
made again through the second, before the sound wave reached 
it. In this way the current could be transferred to all the 
membranes of the series and the successive breakings and mak- 
ings of contact, as the sound wave passed each’ one, could be 
pleted at the membranes, a spark passed between the metal 
ge and the cylinder and made a fine dot in the lamp black. 
y the side of the point was an electrical tuning-fork which 
traced a sinuous curve of times on the lamp-blacked surteee 
of a 
possible errors, a esult. 
found that immediately in the rear of the cannon the 
eRe eg ee 
