NOTICES AND ABSTRACTS 



MISCELLANEOUS COMMUNICATIONS TO THE SECTIONS. 



Correction of an Error in this part of the Report for 1841. 



In the Addendum to the Report of the Transactions of the Sections in 1839, one of 

 the documents, viz. the Letter on p. 5, from Mr. Phillips to Mr. Nasmyth, dated Au- 

 gust 10, 1840, is incorrectly terminated. The last sentence of the letter should have 

 been in these words: — " Should you, however, instead of this easy and obvious mode 

 of correcting any error of mine, resolve to appeal to another tribunal, the public, I 

 can make no other objection than that I fear you will not have chosen the course 

 most advantageous to your views," instead of " Should you, however, instead of this 

 easy and obvious method of correcting any error of mine, resolve to appeal to another 

 tribunal, the public, I will give you the only proof in my power to offer of an un- 

 biassed mind, by transmitting copies of all the letters I have received from you, to 

 render any statement you may think proper to make as complete as possible." 



The mistake was pointed out by Mr. Nasmyth, in a communication to the Presi- 

 dent, dated June 7th, 1842, and appears to have occurred in the following manner : 

 — There was a prior draft of the same letter, and this by some mistake was preserved, 

 and after a very long interval of time was, with other documents in Mr. Phillips's 

 possession, bearing upon the subject, sent to be examined by the authority of the 

 Council. It was this draft, supposed to have been followed in the actual letter, that 

 the printer copied, and hence the error which Mr. Nasmyth has pointed out. 



MATHEMATICS AND PHYSICS. 



On the Astronomical Clock. By M. Bessel of Konigsberg. 



Having ever been of opinion that the most indispensable of astronomical instru- 

 ments, the transit-clock, will only acquire the greatest possible perfectness, if the 

 pendulum, separated from the wheel-work, is made to vibrate in equal time, whatever 

 the temperature and the arc may be, I beg leave to communicate to this Associa- 

 tion some hints relative to this matter. Some artists have endeavoured to compen- 

 sate a variation of the arc, from summer to winter, by not completely compensating 

 the pendulum for the variation of heat; others have contrived very ingenious means 

 for producing always an equal arc. But experience, at least my own, has shown no 

 so complete success, that astronomers, though they feel themselves truly indebted to 

 the skill and the ingenuity of artists, should not be tempted to wish that further en- 

 deavours might not be considered as useless. 



Some years ago, Mr. Frodsham communicated to this Association a very ingenious 

 contrivance, which he calls the isochronal piece, the purpose of which is to compensate, 

 by the effect of the suspension spring, that of a variation of the arc. Supposing that 

 experiments of this universally celebrated artist have shown this contrivance to answer 

 the purpose, there will be no longer a difficulty in making the rate of a pendulum in- 

 dependent, as well of the arc as of the heat. What I wish to submit to his judge- 

 ment, is only whether the very expeditious method of coincidences might not be em- 

 ployed for checking a pendulum in both respects. The pendulum, without the clock, 

 being suspended from the wall, a clock, taken out of its case, may be placed before it 

 at a distance of 6 or 8 feet ; an object-glass, of 3 or 4 feet focal length, may be placed 

 between both, so that it produces, exactly at the lower end of the pendulum of the 



1842. ' B 



