252 Messrs. Allen and Pepys on the Changes produced in 
into the open air, then applying his lips to the tube, and keep- 
ing his left hand constantly on the cock, fig. i, and his right 
hand on the cock, fig. 2, he opened the communication with 
the water gasometer, and made an inspiration ; then imme- 
diately closing it, he opened with his right hand the cock 
at 2 ; and that at 4 being also opened, he expired into the 
mercurial gasometer G. 1. ; then closing 2, which cut off all 
communication with the mercurial gasometer, he opened 1, 
in order to make a fresh inspiration ; then closing it, he again 
opened 2, and expired into the mercurial gasometer; and 
proceeding in this way, always taking care to shut one cock 
before the other was opened, the air was made to pass from 
the water gasometer, through the lungs of the operator into 
the mercurial gasometer, and this with great ease, as the dia- 
meters of the tubes were purposely made large. The scale 
of the mercurial gasometer was carefully noticed, and when 
nearly full, the cock 4 underneath was shut off : then, by a 
signal from the operator, his colleague opened 3, and the ex- 
pirations were received in G. 2. While this was filling, the 
number of cubic inches in G. 1 was registered, a portion saved 
in the mercurial bath, and the rest quickly expelled. This 
operation was repeated until the contents of about twelve or 
thirteen mercurial gasometers were taken off; the operator 
always concluding with a strong effort to empty his lungs 
as completely as possible. The quantity inspired from the 
water gasometer was then compared with the quantities ex- 
pired into the mercurial gasometers, and the difference noted. 
The following are the results of the first ten experiments. 
