( IS ) 



obfervations, partly becaufe it is very rare to find a piece fplit out 

 fo long, and fo t!iin with the perpendicular veiTels lb clearly difcern- 

 ible in it without obllru^tion to the fight from tlie horizontal ones, 

 and partly becaufe I have feldom found fo many of the globules in 

 fo fmall a fpace. Thefe globules in my opinion are the fubfiance we 

 call Turpentine, and from which, by biu'ning the wood, Pitch and 

 Tar are procured.* 



Between DE and F, are to be feen the tubes of the wood when 

 divided, which plainly appear to be fplit, not exaftly ftrait in length', 

 but in a manner indented or jagged and broken fidewa3's. 



I alfo put into the Engraver's hands two feparate microfcopes that 

 he might make diftin6l drawings of thefe tubes of the wood, and 

 from one of thefe was taken /^. 9, M N, where two of fuch tubes 

 are reprefented when fplit lengthways ; but the Engraver faid that 

 he could not pofTibl}' draw all the jagged parts which he faw. And 

 we both of us perceived in the broken membrane or coat of the tube; 

 many excellively minute veflels, which by reafon of their fmallncfs 

 he was unable to exprefs in the drawing. Fig. 10, O P, rcprefents 

 a fingle tube of the wood, in which, as plainly as could be done, is 

 reprefented the broken parts of the membrane of which the tube is 

 chiefly compofed. 



Since then we find by thefe obfervations, that the very fine mem- 

 branes of which thefe woody tubes confift, is not always fplit length- 

 ways, but often in an indented or jagged form, we may eafily cozi- 

 ceive that the tubes of wood, however minute they be, are partly 

 formed fimilar to the quills of feathers. 



* It is well known, that TLirpcntinc is procured from the Fir, by making a wound or incifion 

 in the Tree, from whence the Turpentine flows in great alnindance. This, upon being diftillcd 

 produce^ the fpirit of Turpentine, and what remains at the bottom of the ftill, is the fubliancfr 

 called Rofin, — Pitch and Tar arc obtained by burning large quantifies of the billets of Fir, either 

 in the open air, covered with fods to prevent evaporation as was the aiKient practice, or in ovens 

 conftructed for thatpurpofc, as is ihe modern method. 



