64 Notices respecting New Books. 



enable them to compare it with the position of M. J. R. Mayer of 

 Heilbronn,in the year before (1842), when he wrote his "Remarks 

 on the Forces of Inanimate Nature." I need scarcely say that 

 such a comparison would be of great interest to me, as I think it 

 would convince your readers of the fact that M. Mayer wrote his 

 "Remarks" in 1842 before he was able to support them by a 

 single experiment, or by anything like a proof of their exactness ; 

 whilst I thought it to be my duty, before I wrote, to prove that 

 my suppositions concerning the forces were confirmed by nature 

 itself as a law of nature. 



I am, Gentlemen, 



Your most respectful and obedient Servant, 

 A. Colding, 

 Engineer in Chief to the City of Copenhagen. 



XII. Notices respecting New Books. 



Practical and Spherical Astronomy , for the use chief y of Students in 

 the Universities. By the Rev. Robert Main, M.A., F.R.S. 

 1863, pp. 392. Cambridge: Deighton, Bell and Co. London: Bell 

 and Daldy. 



npHIS book must not be confounded with the author's translation of 

 -*- part of M. Briinnow's ' Spherical Astronomy.' It is, in fact, an 

 independent work, and complete according to the author's view of 

 what should be comprised in such a treatise. It contains, in the first 

 place, a full account of the methods employed in modern observato- 

 ries of making and reducing observations, with particular reference 

 to the methods used at Greenwich (pp. 41, 54, 58, 85, &c). This 

 is comprised in the first seven chapters. The remainder of the work 

 is of a more miscellaneous character. It is devoted to a discussion 

 of the questions that concern the planets and their satellites, the 

 determination of geographical latitude and longitude, and the pre- 

 diction of eclipses and occultations. These parts, into which the 

 work might be divided, are of about equal length, the former being 

 somewhat the longer. 



It must be understood that the book is intended to give an account 

 of Principles and Methods as distinguished from Results. Accord- 

 ingly wherever a phenomenon is described it is with the utmost 

 brevity, and such questions as the physical constitution of the moon 

 and planets are noticed only to be dismissed. Yet when results are 

 stated, a great deal of information is conveyed in few words, — e. g., 

 the account of the recent discussion of the sun's horizontal parallax 

 (p. 196) ; that of the discussion of the acceleration of the moon's 

 mean motion (p. 279) ; that of Jupiter's satellites (p. 283), &c. 

 In accordance with the same view, the descriptions of the instru- 

 ments are very brief, while the mathematical questions arising out of 

 their errors are given at full length. There can be no question that 

 Mr. Main is quite right in not describing the instruments with extreme 

 minuteness ; still we are compelled to think it a fault that not so much 



