Notices respecting New Books. 215 



The book is better than the mere Cambridge text- book in one 

 particular, viz. that it contains frequent references to the papers 

 compiled from ; and in certain parts of the subject where a purely 

 algebraic treatment is not out of place — as for instance in the 

 details of diffraction — its method is not so unsatisfactory, though 

 even here the diagrams and general explanations are very feeble. 



One peculiarly irritating quality the preface and general text 

 of the book possess, viz. the tremendous superfluity and misplace- 

 ment of commas. If the sentences be read as punctuated they are 

 half unintelligible and grotesquely wearisome. The author seems 

 to be under the impression that a comma must always precede the 

 words ' which/ ' who,' and ' that'; for instance page 190 : — "The 

 general theory of media, which are capable of resisting compression 

 and distortion, is given in treatises on Elasticity ; and it will there- 

 fore be unnecessary to reproduce investigations, which are to be 

 found in such works." Almost any page at random may furnish an 

 example, for instance page 345 : — " If we adopted the first hypo- 

 thesis, it would be necessary to suppose, that k the free period of the 

 matter vibration, lies below the infra-red portion of the spectrum ; 

 if on the other hand, we adopted the second hypothesis, it would 

 be necessary to suppose, that k corresponds to a point in or above 

 the ultra-violet," &e. 



On page 249, " Erom this law we see, that the intensity of the 

 blue light is the greatest. Hence the blue colour of the sky may 

 be accounted for on the supposition, that it is due to the minute 

 particles of vapour, and also probably to the particles of air, w 7 hich 

 scatter the waves proceeding from the sun." 



This last, by the way, is one of the extraordinary statements. 

 Here is another, p. 287 : — 



" It was formerly supposed, that the infra-red portion of the 

 spectrum produced the maximum heating effect ; that the yellow 

 was the most luminous portion; whilst the maximum chemical effect 

 was contained in the violet and ultra-violet portions. More recent 

 investigations have shown, that this view is not correct." 



There was room for a treatise on Physical Optics more advanced 

 than the entirely admirable text-book of Mr. Preston. We venture 

 to maintain that there is still room for such a treatise, and we hope 

 that the work will be undertaken by a mathematical physicist 

 instead of by a mere mathematician. 



A Dictionary of Electrical Words, Terms, and Phrases. 

 By Edwin J. Houston, A.M. 

 Some months ago a learned judge, after ten days' evidence by 

 electrical engineers had been brought before him, asked naively, 

 " What is the difference between an Ampere and a Volt ? " Some 

 days ago, in the Appeal Court, another learned judge, in the third 

 day of a trial concerning electrical engineering, asked, " What is an 

 ampere-hour ? " After ingenious and long explanations had been 

 given to him and his two colleagues by both defendant and 

 plaintiff, it was obvious that the dissatisfaction of the Court had 

 not been altogether removed. 



