80 Properties of Wood Ashes. 



The forces at P and Ct will be expressed by P and Q,, then by 

 taking B and A for the centres of P and Q., we shall have j)=PB, 

 q = Qik, and we shall get Pjo4-Q.g'=PxPB + Q,xQ.A. Again, 

 let the points of application of P and Q, be changed from P and 

 Q, to V and E, these points being taken in the hnes PB, QA, 

 (produced if required,) and such that if we denote P'B by p', 

 and AE by q', we shall have as in (3) Vp -{-Qiq — Vp' -{-Giq' , or 

 (p/_j5)P = (^_^')a, or PxP'P = Q.xEa, (a). Join CP' and 

 produce it to intersect GIA in Q,', then the triangles CPP', QCGl' 



CQ, 



being similar, we get aCl'=Qp X PP', ••. QE = GlGl'— Q.'E = 



ca 



^Tp- X PP'-Q,'E, which substituted in (a) we get Px P'P = 



CQ. 



Q^Xpp-xP'P-Q,xQ.''E, (6). Now since P'P is arbitrary, we 



ca 



must equate its coefficients, •-. P=Q.Xpp-, or PxCP=Q,xCGl, 



which gives the well known law of equilibrium in the lever : in 

 order to satisfy (6), 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 Q,A. 



In a similar way we can easily find the pressure on the fulcrum 

 C, (which 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. 



Art. VII.— J. dangerous Property of Wood Ashes exposed, and 

 some of their other Properties examined ; by Dr. John T. 

 Plummer, of Richmond, Indiana. 



TO THE EDITORS OF THE AMERICAN JOURNAL OF SCIENCE. 



I HAVE recently devoted some time to a further examination 

 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 

 general as well as the scientific reader ; for I cannot forbear think- 

 ing, that at least some of the mysterious conflagrations which are 

 repeatedly occurring, are chargeable to this hitherto unsuspected 

 cause. 



