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Sect. XVIII. 2. 8. LEAVES AND WOOD. 



/ 



521 



e;rand trunk canal, aflured 



me 



> 



that he believed from oh{t 



that red Riga deal, or pine-wood, would endure as long as oak ii 

 fituations," owing perhaps to its being fo full of refin or turpen 



tine. 



8. Other woods differ in the d'egree of the lateral adhefion of thei 

 lo-Itudinal fibres, as the fir-wood, or deal, pinus, whence the tim 



ber readily fplits by wed 



As the moifture of the atmofph 



/ - 



abforbed into the pores of the dry cellular membrane, whch conneds 

 the longitudinal fibres of thefe woods, more than into thofe of the 

 longitudinal fibres themfelves, they become much more dilated la- 

 terally than extended longitudinally, by the change of a dry atmo- 

 fphere to a moift one; whence by joining pieces of deal cut crofs-wife 

 into a rod of fome feet In length, a very fenfible creeping hygrome- 

 ter was made by Mr. Bdgeworth, defcribed in the 



Botanic Gard 



Vol. II 



Imp 



And 



as 



th 



wood 



is 



able to be 



much extended by low degrees of heat, when it is impregnated with 

 boiling oil, or covered with varnifli, to prevent the accefs of aerial 

 moifture, the pendulums of time-keepers have been conftrudled of 

 it, which have not perceptibly lengthened in any variations of the 



heat or moifture of the atmofphere. 



o. Another circumftance pf great confequence, in v 



diffe 



their fpecifi 



or 



ravity 



many of them 



oak aft 



has been Ion 2" moiftened 



o 



d 



e, in which woods 

 will fink in water, 



jrs will fwim with 

 much of their contents above water, as deal, and hence have been 

 ufed for the conftrudion of rafts for the purpofes of rude navio-a- 

 tion ; and which are now faid to be conftrudled in France as eno-inee 

 of war, probably for the defign ( 



f fuddenly landing troops, horfes 



ry, and provifions, from the ftiips of invading armies on dan 



ftiorcs, and for the certainty of re- embark 



^•^ 



b 



th clefs 



can not 



y 



burth 



Thefe 



fimply by their fpecific 



vlty ; but if each piece of timber could be made hollow, and rendered 

 water-tight, fo as to contain air, which might probably be done by 



3X 



boring 



/ 



% • 



