c4 Letter en Astronomical and Philosophical Suljecis. 



son, I assumed for the sake of example, the smallest density of 

 ■stone, 2|, though this was obviously below the real density of 



the rock of the hill ; then -^X — = T=^i> would be less 

 than the density of the earth, as the numbers to be adopted til! 

 we could know the real density of the hill. 



** Many years after this, a lithological survey was made of the 

 bame hill by Professor Playfair, who found it to consist of rocks 

 of a great variety of densities from 2*5 to 3-2, the medium being 

 about 2| or 2'8. Assuming the former number then 2^, as the 

 density of the hill ; then ?. x 2|. = -H = 4-J-^, or nearly 5, results 

 for the mean density of the earth. And this result, instead of 

 the former, I substituted in its proper place in my abridged edi- 

 tion|of the Philosophical Transactions, from the beginning, to the 

 end of 1800, in eighteen large quarto volumes, where it may be 

 seen. If we assume 2-8, instead of the 2| above used, then 

 •§- X 2-8. = 5*04 comes out for the density of the earth, a little 

 above 5, as the former was a little below it. I fixed therefore on 

 the number 5, as my result for the mean density of the earth, 

 determined by my calculation. The same conclusion is also given 

 in my Tracts in the first memoir of the second volume, where the 

 whole process is stated at large, as may be seen in the set of those 

 Tracts now presented along with this letter ; and as they were 

 also formerly presented to the Royal Institute. 



" And now, after all these evidences of my being the first, and 

 only person, who had calculated the mean density of the earth 

 from the original measurements, and have been considered and 

 acknowledged as such for almost half a century, the world must 

 be astonished to perceive the honour of that determination in 

 danger of being transferred to another person who never ex- 

 pected nor desired it, unless the accidental mistake or misnomer 

 in the Connaissance des Terns be acknowledged and corrected. I 

 hope and trust therefore, from the known honour and liberality 

 of your character, that the mistake will be corrected in the next 

 Number in the Co?maissance des Terns for 1822*. 



*' I hope you will pardon my troubling you with this long let- 

 ter, and so many minute particulars. But old men, who can en- 

 joy but little of the present, and expect still less from the future, 

 live chiefly in retrospect. In my humble walk in life, my chief 



* That Number of the Conna'issance das Temx has been lately published, 

 but without any direct notice of the mistake above alluded to ; and even in & 

 new memoir, similar to the former, not only is tiie mention of the very name 

 and experiment omitted, but special commendation is bestowed on another 

 far inferior experiment by Mr. Cavendish, performed by an apparatus, 

 which was prepared by the inventor of that experiment, the Rev. Mr. Mi- 

 thcli.— Feb. 182U. 



gratification 



