. ( 1^ ) 



In refleoling upon the nature of the tubes or veflels of which wood 

 confilts, I confidered with niyfelf, whether each of thefe tubes was 

 not formed of two difl;in6t kinds of exceflively fmall veflels or coats, 

 one fort extending lengthways, and the otlier fort encompaffing 

 each tube in a circular direction, as I had obferved the quills * of 

 feathers to be formed, in order to give to each tube a degree of 

 firength and firmncfs. 



To inveftigate this, I examined feveral kinds of wood, and 

 particularly the Fir, and at length I obferved in fplitting the 

 larger tubes or veflels of the wood, that fome of them were in- 

 dented or jagged in the fplitting, and I alfo imagined tliat I faw 

 the tube to confift of fmaller veflels in a (trait perpendicular direction 

 which were not difFufed all over the membrane or coat, but only 

 placed on each fide of it, whence I gathered, that though the minute 

 veflels, fome of which 1 conceived to extend longitudinally, and 

 others toencompafs each tube of the wood, cannot always by reafon 

 of their exceeding fmallnel's be difcovered, yet that the tubes are in 

 reality formed like the quills of birds in order to give them the greater 

 ftrength. 



In further profecuting this inquiry, I procured a piece of the Pitch 

 Pine or Fir newly felled, and whicli had been of very quick growth ; 

 and having placed a fmall part of it before the microfcope, I dire6ted 

 the Engraver to copy the figure of it as exactly as poflible. 



Fig. 8, ABCDEFG, reprefents this fmall piece of wood, which 

 I fplit longitudinally as thin as poflible. It's extreme thinnefs brought 

 clearly into view a great number of globules contained in the veflels 

 of this wood, and which aiford a mofl: pleafing fpediacle, not only 

 on account of th.eir exaft globular figure, but alfo becaufc in each 

 of the globules is a lucid or bright fpot. 



I1iis fmall piece of wood I found particularly eligible for my 



* The Author's examination of this fubje£t will apprar in the courfe of the work. 



Ba 



