198 Mr. T. S. Davies on Geometry and Geometers, 



diffusion product. These last experiments were made at an 

 early period with another object in view, namely, to ascertain 

 whether in closely related salts, such as the present sulphates 

 of magnesia and zinc, the two salts might be elastic to each 

 other, like the particles of one and the same salt, so that one 

 salt might possibly suppress the diffusion of the other, and 

 diffuse alone for both. The experiments lend no support to 

 such an idea. 



It appears from all the preceding experiments, that the in- 

 equality of diffusion which existed, is not diminished but ex- 

 aggerated in mixtures, a curious circumstance, which has also 

 been observed of mixed gases. 



[To be continued.] 



XXIV. Geometry and Geometers. ■ 



Collected by T. S. Davies, Esq., F.R.S. and F.S.A.* 



No. VI. 



AS I have had frequent occasion to speak of Dr. Matthew 



^*- Stewart in the earlier portion of these papers, it will be 



proper here to make one statement more. 



From the character of his General Theorems, I have long 

 entertained the opinion that Dr. Stewart had discovered a 

 considerable number of Porisms besides those printed in his 

 book, and the two he gave to Dr. Simson. The description 

 of his MSS. given by Playfair, in his memoir of that illus- 

 trious geometer, led me to believe that it would be possible 

 to make out not only the propositions but likewise their de- 

 monstrations, somewhat in the manner that I did with the 

 Porismatic part of his General Theorems in the Edinburgh 

 Transactions a few years ago. I consequently applied to 

 an eminent mathematical archaeologist to obtain for me infor- 

 mation as to what had become of those papers, and whether they 

 were accessible for such a purpose. In a short time he sent me 

 the copy of a letter from the proper custodian of the papers, 

 decisive on this head. They are all destroyed — deliberately 

 burnt; and not only his, but likewise all the MSS. of his son 

 Dugald Stewart. Into the motives for this act, which its perpe- 

 trator offers, I will not enter ; and shall only state that he was a 

 descendant of those two men whose writings he has thus irre- 

 trievably destroyed. I have thought it desirable to put upon 

 record this fact : for though public indignation will not restore 

 the lost treasures, it may prevent others from imitating the 

 incendiary. 



A great portion of the correspondence with Nourse and 

 * Communicated by the Author. 



