BOOK III. CHAP. VII. 665 



the earth, which is fiippofed 3 1 miles higher at the Equator, than at the 

 Poles. Hence, in traveling towards the line, it is found that clocks with 

 long pendulums (exclufive of what is allowed for rarcfadtion by heat) go 

 too flow, as Dr. Halley, Mr. Richer, and other aftronomers, obferved, 

 who were o iliged to fhorten the pendulums of their clocks before they 

 could make them keep true time; according to Mr. Richer's experiments, 

 the pendulum, to vibrate feconds under the iEquator, muft be about one- 

 tenth of an inch fliorter than In the Northern latitudes ; without which, 

 the clock which it regulates, will lofe between two and three minutes a 

 day. The diiference caufed by the expanlion or lengthening the pendu- 

 lum by heat, has fometimes amounted to about the fortieth part of an 

 inch ; which in many vibrations will make a confiderable alteration in 

 time. It is neceflliry, therefore, that both the clocks and watches, in- 

 tended for ufe in this climate, (hould have their pendulums duly ad- 

 jufted to this variation, and the curvature of the earth; after which, they 

 may be regulated tolerably well by a thermometer, remarking the differ- 

 ent ftates of heat and coolnefs in the air, at which they appear to vibrate 

 loo flow, or too faft. 



The experiments made for dlfcoverlng the expanfion of fluids, were 

 tried by comparing the abfolute weight of a cubic inch, of feveral forts of 

 bodies, in fummer and winter in Europe, of which the following table 

 gives the rekilt in regard to a few, which fliews the difference to be con- 

 fiderable ; and we may reafonably prefume, that the flime bodies are 

 rarely in the Weft Indies lefs rarefied, than they appear to have been in 

 Europe by the fummer's trial, and that in the hotter months they are 

 much more fo. 



Proof fpirit of any kind weighs feven pounds twelve ounces j!5^r gallon. 

 Vol. III. 4 Q But 



