546 



SCIENCE 



[N. S. Vol. XXIX. No. 744 



and! ends witli a brief description of radio- 

 active phenomena. This, together with inter- 

 esting historical and practical matter, is con- 

 tained in an appendix. The main body of 

 the work is almost entirely taken up with the 

 older and more fundamental portions of the 

 pure science and some of its most important 

 applications. The lectures are illustrated 

 with abundant, but not too numerous, experi- 

 ments, most of which are both excellent in 

 themselves and described in a clear and in- 

 teresting way. Many would do well to fol- 

 low the author in his extensive use of the 

 gold leaf, or aluminium' leaf, electroscope 

 provided with a scale; in discarding the tor- 

 sion balance for a more modem instrument; 

 in the use of amber as an insulator; and in 

 the use of a straight wire sliding on metal 

 rods across a magnetic field to show the 

 motional electromotive force — all of which 

 are fortunately becoming more and more 

 common. The general plan of the work is 

 good. Its style, though ordinarily clear, is 

 marred by many obscurities' and other infelici- 

 ties of expression, many of them due to 

 clumsiness of translation. Perhaps the most 

 obscure paragraph in the book is that in 

 which the action of the Holtz machine is ex- 

 plained. The author is particularly unhappy 

 in the character and extent of his nomen- 

 clature for potential and fall of potential, 

 same of his names for these quantities being 

 electroscopic state, degree of eleetroscopic 

 state, degree of electrification (even when the 

 point whose potential is referred to is not on 

 an electrified body), degree of electricity, 

 intensity of electric field, measure of the de- 

 gree of electrification in units of work, fall of 

 electricity, fall of potential, polar difference, 

 fall of the stream. This, however, is much 

 the worst case of the kind that occurs. We 

 read that a hollow metal ball can absorb elec- 

 tricity, that electricity is a puzzling force, 

 that electric forces act on each other, of the 

 conversion of electricity into work, and vice 

 versa; and we find many other expressions 

 entirely out of place in a work aiming to be 

 scientific, and very objectionable anywhere 

 else. The author wisely devotes but slight at- 

 tention to the consideration of hypotheses; 



and fortunately, as it seems to the reviewer, 

 for his treatment of several at least of those 

 taken up appears far from sound. It is a 

 more serious matter that the book is in 

 error as to many matters of fact and theory 

 too well established to question. Thus, for 

 example, a very curious and erroneous explana- 

 tion is given of the action of flames in dis- 

 charging electrified bodies. Electric absorp- 

 tion is explained by the statement that the 

 spark discharge takes place so quickly that aU 

 the electricity can not follow and a residuum 

 remains. The influence machine is classed 

 with the dynamo as a highly efficient source 

 of electricity. The great advantage of the 

 D'Arsonval galvanometer, called the solenoid 

 galvanometer, is said to be that it does not 

 have to be set up with its coil in the mag- 

 netic meridian. Self induction is explained 

 as a particular case of mutual induction. All 

 dynamos are said to give the best results 

 when the resistance in the service conductor 

 is equal to that in the winding's of the ma- 

 chine, and we are told that stronger hard- 

 soldered thermopiles are specially suitable 

 for the charging of accumulators. One of the 

 first errors made in the book is in the discus- 

 sion of an experiment on capacity, which the 

 author mistakes for an experiment on poten- 

 tial — a quantity which has led astray so many 

 writers of elementary books. In this connec- 

 tion we read, as we have read in other books, 

 that a positive body gives up electricity to the 

 earth and that a negative body receives elec- 

 tricity from the earth; but we are not told 

 what the earth itself does when it is either 

 positively charged or negatively charged. 

 No correct definition of the electromotive 

 force of a generator is given, and no satisfac- 

 tory derivation of Ohm's law for a closed 

 circuit. Under the circumstances we are not 

 surprised to read that Ohm's law does not 

 hold for alternating currents. These matters 

 are so fundamental, and so easy to treat prop- 

 erly, that the remissness of text-book writers 

 is hard to understand. The statements in 

 the appendix with reference to what should 

 be called the electric intensity and the electric 

 tension at the surface of a charged con- 

 ductor are anything but satisfactory. The 



