TWENTY-SIXTH CONGRESS, 1839-41. 235 



perhaps to direct him in some degree, and with the duty of reporting to 

 the governing body. 



The visitors of the Cambridge observatory are all members of the senate 

 of the university. The visitors of the G-reenwich observatory are persons 

 living in different parts of England, 



6. At Cambridge observatory there are two assistants and a laborer. 

 At the Cape of Good Hope, the same. 



At Edinburgh, Dublin, and Armagh, I believe one assistant each. 



Their duties are to observe and to calculate, under the direction of the 

 astronomer. 



The salaries of the Cambridge assistants arc, I think, £80 each per an- 

 jium, with apartments. 



7. The instruments at Cambridge observatory are — 



A mural circle, 8 feet in diameter, made by Troughton ; price, £1,050. 



A transit instrument, 10 feot long, made by DoUand ; price, I believe, 

 £600. 



An equatorial 5-feet telescope, made by Jones ; price, about £750 ; (many 

 complaints of this price.) 



Several small instruments, telescopes, &c. 



Three clocks ; one cost £100 to £120. 



A 20- feet telescope, presented by the Duke of Northumberland. 



At Oxford there are some quadrants, not used ; and also a circle, 4 feet 

 diameter, made by Jones ; and an old transit. 



At Edinburgh : a mural circle, 4 feet in diameter, made by Simms ; and 

 a transit, made bj' Rcpsold, of Hamburgh. 



At Armagh : a mural circle, 4 feet in diameter, made by Jones ; and a 

 transit, (maker not known.) 



At Dublin : an altitude and azimuth instrument ; the vertical circle, 8 

 feet in diameter, made by Kamsden ; and a transit. 



I may remark, that, in the construction of instruments, expense may 

 frequently be avoided by leaving some points to the discretion of the instru- 

 ment maker. As an instance : when I superintended the equatorial mount- 

 ing of the 20-feet telescope at Cambridge, I found occasion for a 5-feet circle, 

 and I directed it to be cast in one piece of boll metal. It appears to answer 

 perfectly well. Mr. Simms is quite satisfied with it, and thinks it possible 

 that it might be made, at still less expense, of cast-iron. Since that time, 

 Mr. Simms has had, I believe, two orders for large circles ; and when I 

 have urged him to have each cast in one piece, he has expressed his wish to 

 do so ; but has informed me that his orders were to make them " like the 

 Greenwich circles," and has therefore considered himself compelled to put 

 them together in many pieces, in the same way as the Greenwich circles, at 

 much greater expense than would have been implied in the construction 

 mentioned above. 



G. B. Airy. 



June 8, 1839. 



Since writing the answers above, I have received from Mr. Simms the 

 following list of prices : 



The mural circles for Greenwich, Cracow, Brussels, Edinburgh, and 

 Lucknow, are all of the .same dimensions, (six feet in diameter.) and were 

 all made by Troughton. The price in each case was £735. Mr. Simms 

 states that at this price there was no profit, (Troughton was wholly regard- 

 less of profit in constructing these instruments,) and that he would not like 

 to undertake one for less than £900. 



The mural circle for Cambridge, eight feet in diameter, was made by 

 Troughton, for £1 ,050. 



Troughton was paid for the Greenwich transit £315, which sum did not 

 includethe object-glass. Mr. Simms states that the cost now would be 450 

 guineas for the instrument complete. Its length is ten feet. 



Troughton received for the Brussels equatorial 450 guineas ; but this was 

 too little ; it ought to have been £600. (I think that the length of the tel- 



