764 Col. Roy’s Experiments for 
fituation on the globe for conclufive equatorial obferva- 
tions; but as it would be found very difficult to carry any 
fcheme of that kind into execution, fuch as may be more 
eafily obtained in our Weft India iflands, which have the 
higheft mountains, would be very fatisfactory with re- 
fpe£t to the expanfion and weight of moift air, at dif- 
ferent heights above the lurface. At the tops of the 
mountains in the torrid zone, the obfervations would 
always be fufficiently cold; but it would be of ufe like- 
wife, to have the coldeft poflible at the level of the fea, 
under or near one of the tropics, when the Sun was ip 
the other. 
With regard to obfervations in the frigid zones, Spitz- 
bergen feems to be as proper a fituation as any ; though 
others may no doubt be found in the Northern parts of 
the Ruffian empire: and it is prefumed, that the Pe- 
terfburg academy would direct the experiments to be 
made. 
acceflible to man, by confldering the height above the fea of the inferior line 
of perpetual fnow. In the middle of the torrid zone it appears, from Mr. 
bouguer s obfervations, to be elevated 5201 yards, and 4476 about the tro- 
pics. In middle latitudes there is eyerlafting fnow on the mountains at the 
height of 3300 yards. In the latitude of 8o° North, Lord mulgrave found 
the inferior line of fnow to be only about 400 yards above the fea: whence we 
may conclude, that the furface of the earth, at the pole itfelf, is for ever 
covered with fnow. 
5 
The 
