516 Notices of Books. [October, 



while the estimates given by Ptolemy and Alfonso X. approach 

 235,000 miles. Tycho Brahe calculated the distance as 223.000 

 miles. The real distance, deduced by Professor Adams from 

 the observations of Breen at the Cape of Good Hope, would 

 appear to be 238,818 miles. We may roughly take the moon's 

 diameter as two-sevenths that of the earth, the moon's surface 

 as twenty-two-sevenths, and her mass at two-ninety-ninths. The 

 surface would be about equal to that of Europe and Africa to- 

 gether, or of North and South America taken together. The 

 earth's disc, as seen from the moon, would appear to be 13^- times 

 larger than the moon appears to us. 



The second chapter, which treats of the moon's motions, is 

 one of the most important in the book. It discusses the subject 

 in many points more fully either than Sir G. B. Airy (in his 

 article " Gravitation "1 or Sir John Herschel lin his " Outlines 

 of Astronomy "). This chapter occupies nearly one-fourth of the 

 entire work, and it is fully illustrated by designs of the author ; 

 among others, illustrations of the advance of the perigee and 

 the retreat of the nodes. It is altogether an elaborate exposition 

 of a most difficult subject, which has engaged the attention of 

 the most eminent astronomers and mathematicians of the last 

 century and a half. Our author says, in conclusion, " In the 

 whole history of the researches by which men have endeavoured 

 to master the secrets of Nature, no chapter is more encouraging 

 than that which relates to the interpretation of the lunar 

 motions." 



In the account of the study of the moon's surface we have 

 some interesting details concerning the colour of the moon. As 

 to the general results of telescopic observation of the surface, 

 we have to remember the circumstances under which they are 

 made and the power applied. " The highest power yet applied 

 to the moon (3. power of about six thousand* brings her, so to 

 speak, to a distance of 40 miles — a distance far too great for 

 objects of moderate size to become visible. Many of my readers 

 have probably seen Mont Blanc from the neighbourhood of 

 Geneva, a distance of about 40 miles. At this distance the pro- 

 portions of vast snow-covered hills and rocks are dwarfed almost 

 to nothingness, extensive glaciers are quite imperceptible, and 

 any attempt to recognise the presence of living creatures or of 

 their dwellings (with the unaided eye' is utterly useless." . . 

 Again, as to other difficulties, "We view celestial objects through 

 tubes placed at the bottom of a vast aerial ocean, never at rest 

 through any portion of its depth ; and the atmospheric undula- 

 tions which even the naked eye is able to detect are magnified 

 just in proportion to the power employed. These undulations 

 are the bane of the telescopist. What could be done with 

 telescopes, if it were not for these obstructions to perfect vision, 

 may be gathered from the results of Professor Smyth's observa- 

 tions from the summit of Teneriffe. Raised above the densest 



