thermometrical barometer for measuring altitudes. 1 95 
being equal to 0,589 inch, whether a scale of the common 
or thermometrical barometer, an equal precision may, I think, 
be attained ; and with a power considerably increased, the 
instrument will always be much more portable than a com- 
mon barometer, although the scale should be extended for 
taking the greatest known heights by a single pair of obser- 
vations. 
F. J. H. WOLLASTON. 
Southweald, March i, 1817. 
P. S. Since the above account was written, two heights 
have been measured with the instrument there described, 
which agree with the measurements made by General Roy. 
March 21, 1817, the thermometrical barometer boiled in a 
house on the edge of the wharf at Scotland-yard, and on a 
level with the wharf, stood at 780, thermometer 41, barome- 
ter 29,98. Boiled on the same morning in the Dining-room 
at the Spaniard at Hampstead, it stood at 599— thermometer 
37— on the road to Hampstead, thermometer 39 — mean ther- 
mometer 39. Difference of stations 181. 233:535:: 181 : 415. 
Correction to be added ~~ of height =2 725 feet. Corrected 
height = 422,25 feet. Made by General Roy 422 feet. 
April 3, 18 17. The thermometrical barometer boiled in Mr. 
Dolland’s back shop in St. Paul’s church-yard, 4 feet above 
the north pavement, stood at 886, barometer 3041, thermo- 
meter 57. Out-doors below, and on Stone Gallery, and on Gilt 
Gallery of St. Paul’s, thermomer 60, therefore thermometer 
taken at 60. In the Gilt Gallery, 2 feet above the floor, the 
