86 Notices respecting New Books. 



leading or principal terms which may occur upon an incomplete 

 examination : hence also the extreme practical difficulty of the 

 problem in whatever manner it be approached. 



" In the method which M. Plana has adopted, first, the mean lon- 

 gitude of the moon is obtained in terms of the true longitude, and 

 the true longitude is afterwards found in terms of the mean longi- 

 tude by reversion. But the divergence of the numerical coefficients 

 exists equally in the former expression, and does not arise in the 

 operation of reversion." 



A note is appended " On the Calculation of the Distance of a Comet 

 from the Earth." Sir J. Lubbock having in his former Treatise on 

 that subject (noticed in our fourth volume, p. 219) considered the 

 position of the comet and of the sun to be denned by longitude and 

 latitude, deduces, in this note, from the equations given in that trea- 

 tise, those which must be employed if the positions of the comet 

 and sun are defined by right ascension and declination ; after which 

 he successively examines the equations of Legendre and Lagrange 

 (showing the former to be preferable), notices the equation recom- 

 mended by Mr. Airy, and the solution of Laplace ; and concludes 

 as follows : — 



" If observations of right ascension and declination be employed, 

 the trouble of calculating the observed longitudes and latitudes is 

 avoided, but additional terms are introduced explicitly into the final 

 equations from which the distance of the comet is sought, and 

 which may be considered as identical, whichever data are em- 

 ployed." 



An Essay on Single Vision. By Dr. Woodhouse, Fellow of Caius 

 College, Cambridge. Weale, 59, High Holborn, 1841. 



This subject belongs to a class of questions intermediate be- 

 tween Natural Philosophy and Pathology, the research of which 

 as a branch of science has been recommended by Bacon in his 

 Novum Organum. 



Suggestions on this particular question have been made by New- 

 ton, Harris, Wood, Herschel and other optical writers, but which 

 cannot be considered as completely accounting for the pheno- 

 menon. 



The author considers " that the parts immediately acted upon by 

 any exciting power, do perceive." This position admits of dispute ; 

 it is well known that during the Taliacotian process, an injury in- 

 flicted on the new-made nose is felt on that part of the forehead 

 from whence the skin had been removed (see Johnstone on Sensa- 

 tion). We have only room to notice two, out of many ingenious 

 experiments by the author. Let C be an object looked at, and 

 P one interposed. Two images of P will appear. If P be moved 

 towards C, those images will mutually, and equally approach towards 

 coalescing. 



Exp. 2. Let a candle be placed a few feet from the observer, and 

 let him look at a pencil between the candle and his eyes ; two 

 images of the candle will appear : but, contrary to the first experi- 



