19 



by the commonest workman, we have 



1 . Hooke's pump gives x = 0. 3, Exhaustion = 96 times. 



2. Smeaton's, - - - - 0. 201, - - - - 146. 



3. Haas's, 0. 001, - - . - 28800. 



4. Kiernan's, - - - - 0. 096, - - - - 30O. 



5. Prince's, - - - - 0. 001, .... 28800. 



6. That described above, 0. O0O32, - - - 90O0O. 



7. Same as in last paragraph, 0. 000002, - - - 14400000. 

 These high numbers are of course only arithmetical expressions 



of the theoretical value of the instruments ; the second and fourth 

 are below the performance actually obtained, while the fifth and all 

 yet constructed of the sixth must fall short of what I assign to them ; 

 it remains to find whether mine will approach nearer to the limit. 



T. R. ROBINSON. 



October, 26, 1822. 



i>2 



