42 Dr. T. Thomson on Pyroxylic Spirit and its Compounds. 



For, by the theory of transversals, (Carnot, Essai sur la 

 Theorie des Transversales, Theor. V.), 



AF.BD.CE = FB.DC.EA. 

 But (Euc. III. 35. or 36.) 

 .^ AE.AE' ^ BF.BF ,^^ CD. CD' 

 ^^=~AnF~' ^^= -B"D^'^"'^^^=~CF~- 



Substitute these in the first member of the preceding equa- 

 tion, and free the result of fractions : then, dividing by the 

 quantities common to both members, we get 



A E' . B F . C D' = C E' . A F . B D'. 



Hence, by the theory of transversals, (Carnot, Essai sur la 

 Theorie des Transversales, Theor. V.), 

 A D', B E', C F' all pass through the same point. 



Cor. Hence, by supposing D and D', E and E', F and F' 

 to coincide, it follows, that the three straight lines drawn from 

 the angles to the points in which the sides touch the inscribed 

 circle, pass through the same point; and the same holds re- 

 garding the points of contact of any of the circles touching 

 a side and the continuations of the other two. 



Several curious questions and considerations, arising from 

 this theorem, will naturally suggest themselves, particularly 

 some regarding loci. I shall not, however, enter on such in- 

 quiries at present. 



IX. On Pyroxylic Spirit and its Compounds. By Thomas 

 Thomson, M.D., F.R.S , Sfc. and Regius Professor of Che- 

 mistry in the University of Glasgow.'^ 

 "p\UMAS informs us that this remarkable substance was 

 ^-^ discovered by Mr. Philip Taylor in 1812, but that he 

 did not make it known to the public till 1822, in a letter 

 to the Editors of the Philosophical Journal f. Never having 

 seen this communication of Mr. Philip Taylor, I do not know 

 the evidence:}: which he has brought forward in proof of his 



* From his " Chemistry of Organic Bodies — Vegetables," p. 346. 



f Chimie appliquec aux Arts, v, 422. 



X [See L. is: E. Phil. Mag. vol. vii. p. 395, 427; vol. viii. p. 85. If Dr. 

 Thomson will refer to vol. Ix. p. 315. of the Phil. Mag. and Journal 

 (for Oct. 1822), quoted by M. Dumas merely as the Philosophical Journal, 

 he will find Mr. Philip Taylor's statement that this spirit was known 

 to him in 1812; and some years before he published this account of it 

 in 1822, I had received a portion of it from him. I feel satisfied that 

 Dr. Thomson must be in error as to dates when he mentions that he was 

 in the habit of using it in 1816; lam certain that it was not employed in 

 London at that period, and what proves this almost to demonstration, is the 

 following addition to Mr, Philip Taylor's announcement of his discovery : 

 " I have sent Mr. Garden, of 372, Oxford-street, some of the pyrolig- 



