[ 68 3 ] 
of by theChemifts in many of their Operations. Be- 
Ildes, all the above Inftruments, being made of 
Glafs, are eafily broken by Accidents, and as liable 
to crack of themfelves, by being taken out of a 
great Heat, and too fuddenly expofed to Cold. I 
therefore confider'd whether the above-menrion’d 
Property of Solids, and cfpecially of Metals con- 
trafting with Cold, and expanding with Heat, might 
not be applied to. the Conftruftion of an Inftrument 
capable of meafuring all Degrees even of the greateft 
Cold, as well as the greateft Heat, to the melting 
Copper or Iron, which require more Heat than any 
other Metals to melt them. Altho’ the Alterations 
in Metals are but fmall, in refpedt of thofe in Spi- 
rits, or even Mercury , yet it being found, that Iron, 
e.g. becomes ^ longer * when red-hot, than when 
of its natural Temperature ; and Dr. ‘Derham, in 
his laft Paper read before the Royal Society concern- 
ing the Vibration of Pendulums, fays, that a Rod 
30.— Inches long, becomes — Inch longer than its 
natural Dimenfions in temperate Air, by being ex- 
pofed to Heat equal to that of an human Body $ 
r |^ Inch longer in hot Sunfhine 5 that it was T ^. or j, 
Inch longer than its natural State, by being heated in 
a flaming Heat 5 that it became ^ fhorter than its 
natural Length by being quenched in cold Water j 
and ftill fhorter, by being put into a Mixture of 
Salt and Snow. From which Experiments one may 
conclude, that from Fahrenheit's Cold of 40 below 
o. to the greateft Heat Iron can bear without melt- 
ing, a Rod of three Feet long will have about ~ Inch; 
Increafe 5 which Increafe of Length will be Range 
enough 
* Vide Sturm „ Call, 
