509 



that I have used as an illustration a series computed by that very 

 machine. * * *." 



In the same letter Mr. Babbage refers to the following docu- 

 ments : 



Extract from a letter of Mr. Babbage to Sir H. Davy, 3 July, 

 1822, printed by order of the House of Commons. No. 370, 

 1823 : 



" Another machine, whose plans are more advanced than several 

 of those just named, is one for constructing tables which have no 

 order of differences constant (p. 2). 



" I should be unwilling to terminate this letter without noticing 

 another class of tables of the greatest importance, almost the whole 

 of which are capable of being calculated by the method of dif- 

 ferences. I refer to all astronomical tables for calculating the places 

 of the sun and planets. It is scarcely necessary to observe that the 

 constituent parts of these are of the form a sin 0." (p. 5.) 



He refers also to an extract from the Address of H. T. Colbroke, 

 Esq., President of the Astronomical Society, on presenting to him 

 the first medal given by the Society, 1824; and to a description of 

 his machine by the late Mr. Baily, published in Schumacher's 

 ' Astronomische Nachrichten,' No. 46, and republished in the ' Phi- 

 losophical Magazine ' for May 1824, p. 355. This last paper de- 

 scribes fully what could be done by the new contrivance. 



I have ventured to insert this postscript without consulting my 

 colleagues, as it is desirable not to delay the publication. 



G. G. STOKES. 

 London, Oct. 5, 1855. . 



" Report made to the President and Council of the Royal Society, 

 of Experiments on the Friction of Discs revolving in 

 Water." By JAMES THOMSON, Esq., C.E., Belfast. 



[A Committee of the British Association for the Advancement of 

 Science, consisting of James Thomson, Esq., C.E., and William 

 Fairbairn, Esq., C.E., F.R.S., having been appointed "to make 

 Experiments on the Friction of Discs revolving in water, with espe- 

 cial reference to supplying data wanted in calculations relative to 



2 z2 



