meafuring Heights with the Barometer . 663 
in both ends of the fame tube, that the mean might be 
taken. But it frequently happened that the tube, which 
had undergone one or more experiments in one end, 
broke before any could be made with it in the other. In 
this cafe, the rate of expan fion in the lafl: end was taken 
from that given by fuch another tube, where it had fuc- 
ceeded in both. The mean of five refults with the bell 
tubes, taken in this way, gave .4901 for the apparent 
expanfion of 30 inches of quickfilver, on 180° of Fah- 
renheit, between freezing and boiling, which being 
augmented by the apparent longitudinal dilatation of the 
glafs .0356X 3 = .io68, the real expanfion is .5969; ex- 
ceeding Mr. de lug’s by more than ~ths of an inch. If, 
however, Mr. s me aton’s dilatation of glafs, (.023 x 3 = 
.075) be fubftituted, inftead of that refulting from thefe 
experiments, the real expanfion of 30 inches of quick- 
filver will be .5651, which does not exceed it quite 
parts of an inch. 
In this clafs of experiments, having attended as dili- 
gently as poffible to all the circumftances, it feemed to 
me, that tubes with a fmall bore, and whofe glafs was 
thick, lengthened more than thole, which had a larger 
bore and whofe glafs was thin: whence I was led to 
fuppofe, that folid glafs rods would dilate more in pro- 
portion, and confequently, fhew a frill more perceptible 
difference. 
