80 Properties of Wood Ashes. 
The forces at P and Q will be expressed by P and Q, then by 
taking B and A for the centres of P and Q,.we shall have p=PB, 
q=QA, and we shall get Pp+Qg=PxXPB+QxQA. Again, 
let the points of application of P and Q be changed from P and 
Q to P’ and E, these points being taken in the lines PB, QA; 
(produced if required,) and such that if we denote P’B by py 
and AE by q’, we shall have as in (3) Pp-+Qg=Pp’+Q¢’, or 
(p’- p)P=(q—q/)Q, or PxPP=QxXEQ, (a). Join CP! and 
produce it to intersect QA in Q’, then the triangles CPP’, QCQ’ 
> ; CO ex 3 
being similar, we get QQ’=Gp x PP’, .. QE = QQ’—Q’E= 
= x PP’—Q’E, which substituted in (a) we get Px PP = 
Rate» ae een aie coe can alia 
QxGp XPP-QxQ@eE, (6). Now since P’P is arbitrary, we 
must equate its coefficients, .°. P=Q eee, or PxCP=Q xCQ, 
which gives the well known law of equilibrium in the lever: in 
order to satisfy (b), we must also put Q/E=0;. which shows 
that to satisfy the conditions in (3), the point E ought to have 
been taken at Q’, where CP’ produced intersects QA. i 
“ Tnasimilar way we can easily find the pressure on the fulcrum 
C, Grbich is the resultant of P and Q,) and did room permit, we 
could easily deduce the well known principle of the parallelo- 
gram of forces, | : : 
ve: , 
into the properties of wood ashes, and especially into that prop- 
erty by which heat is conveyed.from a small ‘space on their sur- 
face deeply into the interior of the largest. masses, I consider 
the subject of, sufficient importance to claim the attention of the 
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t forhear think-. 
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some of the teri L tions which are 
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