THE MOON. 75 7 



ured by the most skilful artist ; the information conveyed by the 

 telescope is too definite to permit of speculation as with the other 

 planets, yet not definite enough to solve the questions about which 

 the students of astronomical works take most interest ; and the infor- 

 mation which astronomers have obtained from the moon's motions can 

 only be appreciated when those motions are thoroughly analyzed, and 

 it has not been found easy to simplify this analysis, that the general 

 reader might fairly be expected to take interest in the matter. 



The work before us is intended to remove this Ions-recognized 

 want in the literature of astronomy. The time has come when this is 

 practicable. The splendid photographs of Rutherford, of New York, 

 and De La Rue, in England, supply the means of exhibiting truthfully 

 the real nature of our satellite's surface. Mr. Proctor has been for- 

 tunate in obtaining from Mr. Rutherford permission to use three of his 

 most effective photographs of the moon to illustrate the present work. 

 Recent researches, again, into the processes which are going on within 

 the solar system (so long mistakenly supposed to be unchanging in 

 condition), suggest considerations respecting the past condition of 

 the moon, at once bringing her within the range of speculation and 

 theory. Telescopic observations, also more scrutinizing than those 

 made of yore, and applied more persistently, begin to indicate the 

 possibility at least of recognizing the signs of change, and perhaps of 

 showing that our moon is not the dead and arid waste which astron- 

 omers have hitherto supposed her to be. The heat measurements of 

 Lord Rosse also throw important light on the question of her present 

 condition. And then, as respects those points which constitute the 

 main scientific interest of our satellite, her motions under the varying 

 influences to which she is subjected, Mr. Proctor has devoted here his 

 full energies and the results of a long experience, to the endeavor to 

 make clear, even to those who are not mathematicians, the consider- 

 ations which, weighed and analyzed in the wonderful brain of Newton, 

 supplied the means of demonstrating the theory of the universe. 



On this important department of his subject, Mr. Proctor makes 

 the following remarks in his preface : " In Chapter II. I have given a 

 very full account of the peculiarities of the moon's motions ; and, not- 

 withstanding the acknowledged difficulty of the subject, I think my 

 account is sufficiently clear and simple to be understood by any one, 

 even though not acquainted with the elements of mathematics, who 

 will be at the pains to read it attentively through. I have sought to 

 make the subject clear to a far wider range of readers than the class 

 for which Sir G. Airy's treatise on 'Gravitation' was written, while 

 yet not omitting any essential points in the argument. In order to 

 combine independence of treatment with exactness and completeness, 

 I first wrote the chapter without consulting any other work. Then I 

 went through it afresh, carefully comparing each section with the cor- 

 responding part of Sir G. Airy's 'Gravitation,' and Sir J. Herschel's 



