^1^ ON SPONTANEOUS INFL.A MMATIONS. 



1. FriSliGTi, 

 Friftion, It is generally known thaf by rubbing two bodies againft 



each other, they are heated; the intenfity of the produced 

 heat depends on feveral circumftances, and chiefly varies in 

 proportion to the hardnefs of the fridlion, to the nature, and to 

 the furface of the rubbing bodies: if the fridion takes place 

 between combuftible bodies, fucK as the woods, the heat 

 which it excites is frequently fufficient to inflame them: if the 

 bodies are not combuftible, fuch as ftones, or but little com- 

 bufl;ible, like the metals, they do not themfelves inflame, but 

 they can communicate fuch a degree of heat to other combuf- 

 tibles which furround them, that thefe can inflame by the cbn- 

 ta£l of atmofpheric air. 



Dr. Palcani having repeated the experiments which have 

 been long known for obtaining fire by the fridlion of two pieces 

 of wood, to one of which he gave the form of a tablet, and 

 tp the other that of a fpindle or a cylinder, he has allowed me 

 to give the refults of fome of his experimerits here, to fliew 

 that more attention fliould be paid to the choice of the woods 

 which are deftined to rub againft each other, in the conftruc- 

 tion of machines and inftruments. 



Experiments 

 with a tablet 

 between two 

 cylinders, 



Two cylinders of 



Tablet. 



Duration. - EfFea. 



Box-wood ]^;^ Box-wood f;|- 5 Minutes Senfible heat 



Idejn 



Poplar 



Idem Ide7n 



Idem 



Oak 



Idem Ide??i 



Idem 



Mulberry 



3 Minutes Cons, heat and fmoke 



Idem 



Laurel 



Idem Idem 



Laurel 



Poplar 



2 Minutes Jde7H 



Idem 



Ivy 



Idem Idem 



Ivy 



Box-wood 



3 Minutes Idem 



Idem 



Hazle 



J dent Idem 



Olive 



Olive 



Idem Idem 



Mulberry 



Laurel 



2 Minutes Con. he. fm. & black 



Afli 



Oak 



5 Minutes Senfible heat 



Idem 



Fir 



Jdem Idem 



Pear-tree 



Oak 



Idem Idem 



Cherry-tree 



Elm 



Idem Jdem 



Plum-tree 



Apple-tree 



Idem Idem 



Oak 



Fir 



Idem Idem 



On 



