Notices respecting JSew Books. 451 



notice cannot be too highly appraised. From our own estimate of its 

 soundness, and our knowledge of the author's capability of speaking 

 with the highest authority, viz. that of the original investigator, 

 we can only state that Dr. Nietzki's book is alike indispensable to 

 chemist and technologist. 



Lightning Conductors and Lightning Guards, By Oliver J. 

 Lodge, D.Sc, F.B.S.,LL.D. Crown 8vo. London : Whittaker 

 & Co. 1892. 



Dr. Lodge's work on this subject is the result of his having 

 agreed in 1888 to deliver two lectures at the Society of Arts. 

 It is not for the first time that the preparation of such lectures 

 has led to great developments in the practical applications of 

 scientific principles. In this case, the mathematician and physicist 

 owe their thanks to the Society of Arts as well as the mere engineer 

 or person who applies scientific principles to useful purposes. 

 There can be no doubt that Dr. Lodge has effected a complete 

 revolution in our notions as to protection from lightning-discharge. 

 (Five years ago, all engineers and nearly all physicists, in thinking 

 of this subject, applied to it Ohm's law for steady currents. A 

 few telegraph-engineers knew that something more than Ohm's 

 law ought to be applied, and interesting experiments had been 

 made by Prof. Hughes and others. Dr. Lodge has threshed out 

 the whole subject, experimentally and mathematically ; he has 

 encountered much opposition of a kind that was to have been 

 expected ; he has overcome this opposition, and at the present 

 time his views are held to be correct. 



There is no such thing as absolute protection of a building or 

 instrument from evil effects due to lightning-discharges any more 

 than there is absolute protection of a building from earthquakes. 

 Protection is merely a question of degree ; and although Dr. Lodge 

 assumes with Clerk-Maxwell that a powder-magazine " can, if 

 desired, be absolutely protected from internal sparking by enclosing 

 it in a metallic cage or sheath," there can be no doubt that the 

 statement is too absolute. 



A summary of Dr. Lodge's views, which may now T be called 

 the accepted views, is given in Chap. 21 in nine pages, which no 

 practical man will find any difficulty in understanding. The 

 rest of this volume of over 500 pages is mainly devoted to a 

 description of the experiments and other evidence and mathe- 

 matical reasoning which have led Dr. Lodge to hold these views, 

 with the controversial matters which were brought forward by 

 his opponents. 



The experiments are very interesting, and so is the mathematical 

 reasoning. In both, very simple cases are taken to give and illus- 

 trate rather vague general rules for studying the exceedingly com- 

 plicated cases which occur in practice. Until the experiments of 

 Professor Hughes, six years ago, very little attention was paid to 



