364 -Dr. Fouuyce's Experiments on the Lofs of 



I (hall juft take notice of an opinion which has been adopted 

 by Tome, that there is matter abfolutely light, or which repels 

 inflead of attracting other matter. I confels this appears ab- 

 furd to me ; but the following experiment would prove or dif- 

 prove it. Suppofing, for inftance, that heat was a body, and 

 abfolutely light, and that ice gained weight by lofing heat; 

 then a pendulum of ice would fwing through the fame arc in 

 ^^.^-.-^--g. lefs time than a fmiilar pendulum of water ; for the 

 fame power would not only a6t upon a lefs quantity of matter, 

 but a counter-a6l:ing force would alfo be taken away. 



Till the experiment of the pendulum can be made, or fome 

 other equally certain be fuggefted and made, it would be waft, 

 ing time to enter into conjecture about thecaufe of the gain of 

 weight in the converfion of water into ice in a glafs veflel her- 

 metically fealed. 



I fhall only obferve, that heat certainly dimlniflies the at- 

 tradlions of cohefion, chemiftry, magnetifm, and electricity; 

 and if it fhould alfo turn out, that it diminifhes the attradioa 

 of gravitation, I fhould not helitate to coniider heat as the 

 quality of diminution of attra^Slion, which would in that cafe 

 account for all its efFe6ls. 



We come,, in the next place, to take notice of the fecond 

 part of the experiment, viz. that the ice gained an eighth part 

 of a grain on being cooled to 12 degrees of Fahrenheit's 

 thermometer. In this cafe, a variation may arife from the con- 

 tradlion of the glafs veflel, and confequent increafe of fpeclfic 

 gravity in proportion to the air. But it is unneceflary to ob- 

 ferve, that this would be fo very fmall a quantity as not to be 

 obfervable upon a beam adjufted only to the degree of fenfibility 

 with which this experiment was tried. In the fecond place, 

 the air cooled by the ice above the fcale becoming heavier than 

 3 the 



