30 EXPANSION OF WOOD by HEAT. 



I took a ftraight grained piece of white hiccory, green, 

 fori could not procure any feafoned, its length 39 inches, 

 and about -f of an inch fquare. This 1 placed in my 

 pyrometer, and kept it fully extended lay a weight 

 iaftened to a ftring, going over a pulley. To the pyro- 

 meter I applied the tube and glaffes of a good compound 

 microfcope, and a micrometer, the value of the fmaller 

 divifions whereof I found to be nearly .00053 P"-''^^ '^^ 

 an inch, each. 



The rod of wood being placed in the pyrometer, I 

 poured fand all around it, heated to about 250 of Fahren- 

 heit, which degree of heat I found the wood would bear 

 without fcorching. On pouring in the hot fand, the rod 

 expanded very much, but foon began to contrad:, even 

 before the find was fenfibly cooled, which 1 fuppofe arofe 

 from the hot fand extrafting the moifture of the wood. 

 it continued to contrad: as the whole grew cool, fo that 

 when the rod had acquired its firfl: temperature it was 

 near 30 of the above divifions fliorter than at firft. I 

 repeated t!.e operation a fecond and third time, and had 

 then reafon to conclude that the wood was nearly as dry 

 as it would become by lying long in a dry air. 1 now 

 let it cool to the temperature of the atmofphere which 

 was 75° and heating the fand to ?oo only, I poured it 

 around the rod. In a few minutes it expanded i 6 divi- 

 fions. In half an ho^^ the fand had cooled to 125, and 

 the rod had contrafted 1 1 divifions. In an hour more 

 the fand was 80 and the rod fhortened full 4 divifions 

 more, being nearly equal to its length when the fand 

 was iirft applied. On the whole 1 conclude that very 

 dry wood expands with heat pretty regularly, though 

 certainly in a much lefs degree than any of the metals 

 or even glafs. 



DAVID RITTENHOUSE. 

 To the Philofophical Society, 



P. S. 



