Experimental Comparifon of Standard Meafurtt, j^g 



mented by the prefenc^ of the matter of light, and, on the contrary, by Its abfence the forma- 

 tion of fugar in them not only retarded, but in every cafe diminijhed. 



(Tt)e conclufion in our next.) 



ir. 



Appendix to Sir GsOJUGS Shucksu&g Er£trN*S Paper * on the Means of afcertaining a 



Standard of IFetght and Meafure. 



(§. 44.) OiNCE the writing of the preceding Memoir, I have had an opportunity of 

 examining three other fcales, divided into inches, or equal parts, of confiderable authority in 

 this country, having been executed by the late Mr. J. Bird. I have alfo compared the 

 old ftandard in the Exchequer, of the time of Henry VII. and which is confidered to be the 

 moft ancient authority of this fort now fubfifting: thefe obfervations, I flatter myfelf, the 

 Royal Society will be defirous of pofFefling. 



(§. 45.) The firft of the abovementioned fcales belonged to the late General Roy,, and was 

 ^urchafed by him at Mr. Short's fale, the celebrated optician; it was ufed by him in his 

 operations of meafuring a bafe line on Hounflow-heath. (See Phil. Tranf. vol. LXXV.) 

 It was originally the pToperty of Mr. G. Graham, has the name of Jonathan Sis son en- 

 graven upon it, but is known to have been divided by Mr. Bird, who then worked with 

 old Mr. SissoN. It is 42 inches long, divided into tenths. With a vernier of loo at one end, 

 and of 50 at the other, giving the fubdivifions of 500ths, and loooths, of an inch. 



(§. 46.) The fecond is in the pofleffion of Alexander Aubert, Efq. and formerly 

 belonged to Mr. Harris, of the Tower; contains 60 inches, divided into tenths, with a 

 vernier, like that of the preceding. It is one inch broad, and 0,2 thick. 



(§. 47.) The third was pre(»ited by Alexander Aubert, Efq. and the late Admiral Camp- 

 bell, Mr. Bird's executors, to^he Royal Society, in whofe cuftody it now remains. It con- 

 fifts of a brafs rod, 92,4 inches long, 0,57 inch broad; and 0,3 inch thick; bearing a fcale 

 of 90 inches, or equal parts, each fubdividcd into lo, with a vernier at the commencement, 

 being a fcale of 100 divifions to loi tenths. Thh has been called Mr. Bird's own fcale, viz. 

 made for his own ufe ; and was the inftrument with which he is faid to have laid off the 

 divifions of his 8-fcet mural quadrants. It is probable that Mr. Bird made many more of thefe 

 fcales, now in the hands of private perfons (one of which, indeed, I faw at the Prefident dc 

 Saron's, many years ago, at Paris), but thofe have not come to my knowledge. 



(§.48.) In comparing General Roy's (Bird's) fcale with Mr. Troughton's, I found 

 42 inches of the former were = 42,00010 inches on Troughton's ; (ths thermometer 5i*,7 ;) 

 36 inches were confequently = 36,00008. 



• Vyhich vws concluded «t p. 105. 



And 



