64 Notices respecting New Books. 



other cause, the tendency has no effect so far as the present ques- 

 tion is concerned ; and, finally, as the tube for a large part of its 

 length is nearly or quite vertical, the horizontal velocity of the as- 

 cending stream cannot fail to acquire the forward velocity of the 

 train. 



The Statement of General Principles and the proofs of particular 

 theorems contained in the text are (it is almost needless to say so) 

 correct as far as we have noticed ; and the student who works at 

 the book conscientiously will doubtless not fail to make it out, 

 though the style does not generally show in any marked degree the 

 power of clear exposition. There is one point which ought not to 

 be left unnoticed, as the author lays considerable stress upon it : 

 he states that he has endeavoured " above all to show that the re- 

 lation of the theory of heat to mechanics should be approached by 

 the student in his earliest inquiries with the same careful thought 

 with which he will surely regard it when his knowledge and his 

 powers have become extended and strengthened." And accordingly 

 the book contains articles in which are explained what is meant by 

 the mechanical equivalent of heat, by the kinetic theory of gases, 

 and one or two other matters. What parts of a subject an author 

 puts into his book is a matter depending so much on his own judg- 

 ment as to be rarely the proper subject of criticism ; but we may 

 perhaps be allowed to record a difference of opinion. It seems to 

 us, then, that the subject of energy of motion presents difficulties 

 to the beginner so great that it is best to give him a fair chance of 

 becoming familiar with it before introducing him to the far more 

 difficult subject of Potential Energy, and accordingly that it is better 

 not to deal with the latter subject in a purely elementary treatise 

 on mechanics. 



Eclipses Past and Future, with General Hints for Observing the Heavens. 



By the Eev. S. J. Johnson. Parker & Co. : Oxford and London. 



1874. 



Mr. Johnson, in the work before us, has added considerably to 

 our prospective knowledge of eclipses, transits, and allied pheno- 

 mena, and has also given us some interesting information relative 

 to ancient eclipses, mentioning that the first of which we have a 

 clear record happened at Nineveh in the year 763 b.c. Noticing in 

 the order of their sequence the most celebrated eclipses of antiquity, 

 and bringing up the catalogue of observed eclipses to the present 

 date, the author gives us two interesting chapters (V. and VI.) : — the 

 first on the prospects of the amateur, showing the paucity of large 

 eclipses in England during the next thirty years ; and the second, 

 " Curiosities in Lunar Eclipses," as bright and black total eclipses, 

 and those in which both luminaries were above the horizon at the 

 time of the moon being eclipsed, an obvious effect of refraction. 

 The first part of the work, in which we have notices of eclipses 

 from the celebrated one of Ho and Hi 2127 b.c. October 13, to 

 a.d. 2381 July 21, contains a large amount of information on an in- 

 teresting branch of astronomy. 



