Dr, Fordyce’s Experiments on the Lofs of 
I fhall juft take notice of an opinion which has been adopted 
by fome, that there is matter abfolutely light, or which repels 
inftead of attracting other matter. I confefs this appears ab- 
furd to me ; but the following experiment would prove or dis- 
prove it. Suppofing, for inftance, that heat was a body, and 
abfolutely light, and that ice gained weight by lofmg heat ; 
then a pendulum of ice would fwing through the fame arc in 
lefs time than a fimilar pendulum of water ; for the 
fame power would not only aCt upon a lefs quantity of matter, 
but a counter-aCting 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 converfton of water into ice in a glafs veflel her- 
metically fealed. 
I fhall only obferve, that heat certainly diminifhes the at- 
tractions of cohefion, chemiftry, magnetifm, and eleCtricity; 
and if it fhould alfo turn out, that it diminifhes the attraction 
of gravitation, I fhould not heiitate to confider heat as the 
quality of diminution of attraction, which would in that cafe 
account for all its effeCts. 
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- 
traction of the glafs veflel, and confequent increafe of fpecific 
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 adjulted only to the degree of fallibility • 
with which this experiment was tried. In the fecond place, , 
the air cooled by the ice above the fcale becoming heavier than 1 
2 the; 
