GRAVITY OF VAPOUR. 161 
experimenting ; though I took all possible care 
to avoid any source of fallacy, and repeated the 
trials on each vapour severally, in order that 
the errors (if any) might compensate each other. 
I may observe also in favour of my results that 
I had great advantages in obtaining a high and 
steady temperature, by reason of a room ca- 
pable of being heated to any degree between 
200° and 250° Fah.; the chamber which is six- 
teen feet square, and nine feet high, formed of 
iron bars, three inches asunder, and beneath 
at the distance of nine feet is the stove for 
heating it. 
Before I began my experiments, I had ne 
knowledge whatever of the methods practised 
by other experimentalists. My experiments on 
the vapours of pyroxilic spirit and acetic acid 
are, I believe, the first that have been obtained. 
The apparatus which I employed consisted of a 
glass tube with a ball at the end; the tube being 
42 inches long, with a bore of ;'; of an inch. The 
capacity of this tube is 4.64 cubic inches, and 
that of its ball 3.46, making together 8.1 cubic 
inches. In some cases I used a similar tube 40 
inches long, and having a bore of nearly #5 of 
an inch. Its capacity is 6.08 cubic inches, that 
of the ball, 4.3 cubic inches, making together 
N 
