312 Notices respecting New Books. 



of (say twelve) kinds of trains have to be described by signal. 

 In such a case an elaborate instrument called the train-describe? 

 lias to be used (p. 158). As well as a description of the Block 

 System, Mr. Barry gives a discussion of the advantages which it 

 possesses over other systems ; and his conclusion is as follows : — 

 "Viewing the block system as a whole, it may be safely said that 

 it has the advantage of being perfect iu principle in so far that it 

 renders collisions impossible provided it be carried out perfectly ; 

 whereas the system of time signalling, even granting that it can be 

 carried into effect without a flaw, gives no absolute security against 

 collisions " (p. 165). 



Perhaps the point which strikes us most forcibly wheu reading 

 such a book as that before us, is the enormous amount of ingenuity 

 that has beeu brought to bear iu working out the details of our 

 present system of locomotion. The need for a large part of the 

 contrivances actually iu use could not possibly have been foreseen ; 

 it could only have come into view as the system was being gradu- 

 ally worked out. Of course, therefore, further improvement is 

 still possible ; and if by any chance we have a railway manager 

 among our readers, we would earnestly recommend to his attention 

 the following suggestion. " Another great improvement woidd be 

 in paying more attention to distinguishing the trains, or, where 

 necessary separate carriages, by boards on which their destination 

 should be legibly painted, placed in positions on the carriage where 

 the boards would be visible when the train is standing at the plat- 

 form. This is particularly necessary on the metropolitan and 

 suburban lines ; but the notice boards on the carriages are usually; 

 very indistinct, as if railway managers were ashamed of them; 

 and they are often so placed that they cannot be seen well at any 

 time and scarcely at all at night'' (p. 280). 



Exercises in Electrical and Magnetic Measurement, ivith Answers. By 

 E. E. Day, M.A. London: Longmans, Green & Co., 1876 

 (small 8vo, pp. 120). 



This book contains an introduction of four pages on the units 

 employed in Electrical Measurements, one hundred and twelve 

 pages of questions, and an appendix of answers. The questions 

 are about 650 in number, and are given barely, without any note or 

 comment. The answers, with very few exceptions, are numerical. 

 The questions have not been framed as exercises for the ingenuity 

 of the student, but are, as the author states, short descriptions of 

 experiments illustrating the fundamental laws of electricity and 

 magnetism, and are for the most part based upon experimental 

 work actually performed in the laboratory at King's College, Lon- 

 don. A single question, taken almost at random as a specimen, 

 will show what the book is better than a long description : — "A 

 battery of 10 similar galvanic cells was joined up in circuit with 

 a voltameter, and it was found that 80 cubic centimetres of hy- 

 drogen were liberated per minute. When an additional resistance 

 of 15 ohms was introduced into the circuit, the volume of hy- 

 drogen liberated per minute was reduced to 50 cubic centimetres. 



