January 8, 1920] 



NATURE 



463 



In the concluding- chapter an account is given of 

 some recent improvements in thermionic devices 

 mainly developed during the war. There are 

 several suggestive methods of testing the effici- 

 ency of radio-apparatus described in the book, 

 some of which are due to the author. There is 

 also, perhaps naturally, a great deal about the 

 law case between the Marconi Co. and the 

 De Forest Radio Co., which ended so triumphantly 

 for Prof. Fleming. We can heartily recommend the 

 hook to all scientific readers. 



(2) The development of the art of radio-com- 

 munication during the war has forced the author to 

 expand his text-book into two volumes, the second 

 M-Iume being mainly devoted to vacuum valves 

 : nd valve circuits. In writing the first volume 

 Prof. Stanlev had in view the needs of wire- 

 less operators and amateurs. He was impressed 

 by the lack of a text-book on electricity and mag- 

 netism suitable for radio-students. We are told 

 that the existing text-books do not discuss suffi- 

 ciently fully induction, oscillatory currents, and 

 the true significance of " magnetic or electric lines 

 of strain in the all-pervading ether." In the 

 author's opinion the electron theory will present 

 fewer difficulties to the student than the "vague 

 fluid theories which it has replaced." The reviewer 

 read, therefore, his introductory chapters, giving 

 an elementary resume of the latest theories, with 

 an open mind and with considerable interest. 



The impression produced on him, however, was 

 very disappointing. The student is at once intro- 

 duced to electrons. He is told that there are lo^^ 

 free electrons in a centimetre cube of metal, that 

 electricity is a constituent of all forms of matter, 

 and that " a unit of negative charge is an electron, 

 and a unit of positive charge, etc." He is told 

 this before negative or positive charges are de- 

 fined. On p. 13 he has to answer the question. 

 If the electron theory is taken as the correct 

 Miie, what is electricity? " Potential (p. 23) is 

 (li fined as follows : " The electric strain in the 

 iier available for making an electric current flow 

 rough the medium is called the electric pressure, 

 potential, and is measured in units called 

 ' \'olts. ' " This is certainly not the academic 

 <li finition of potential, but it is getting perilously 

 ar the "vague fluid theories." We are told 

 at "if two bodies of the same size are charged 

 iiallv with 'positive or negative electrification' 

 rre is no difference of potential between them." 

 ; ills is misleading. It is true in free space, but 

 1 1 there are any other bodies in the neighbourhood 

 i is probably not true. 



Some of the definitions are carelessly given. 

 The joule, for instance, is defined to be the work 

 done by one ampere of current in flowing between 

 NO. 2619, VOL. 104] 



two points, A and B, when the difference of poten- 

 tial between A and B is one volt. Similarly, in 

 the definition of the erg (p. 42), the " per second " 

 is left out. The dielectric constant is defined 

 (p- 55) as " its effect when used as a dielectric as 

 compared with an air dielectric." This is unintelli- 

 gible. The formula for measuring the mutual 

 inductance between two coils (p. 78) is wrong ; it 

 should be M = (Ln— L2)/4. There is a misprint also 

 in the formula for the time given on p. 82. The 

 rest of the first volume is mainly concerned with 

 ordinary radio-practice and is readable. Some of 

 the diagrams are admirably clear. 



In the second volume the author begins, very 

 properly, with a recapitulatory chapter on " elec- 

 trons." The theory of the thermionic valve is 

 mainly concerned with the passage of electricity 

 through gases, and the electron theory explains 

 this admirably. As the author was chief wireless 

 instructor with the B.E.F. in France he is thor- 

 oughly at home when describing the systems and 

 apparatus used by the Allies in their wireless ser- 

 vices. Radio-engineers will find the chapters on 

 continuous wave (c.w.) transmission and on radio- 

 telephony useful. A. R. 



CATALYSIS. 

 Catalysis in Theory and Practice. By Dr. P'ric K. 

 Rideal and Prof. Hugh S. Taylor. Pp. xv + 

 496. (London : Macmillan and Co., Ltd., 1919.) 

 Price 17s. net. 



THE whole subject of catalysis stands in a 

 peculiar position. For many years it has 

 attracted investigators on the purely scientific 

 side, who have added greatly to its scope 

 in respect both of new material and of theo- 

 retical speculation. It is being actively pursued 

 along both lines at the present time. There are 

 also its vast technical applications, many of them' 

 already well known, to which addition is being 

 constantly made, and wherein new fields are 

 rapidly opening up, of which the modern chemist 

 must take cognisance. Yet, in spite of all this, 

 we should be hard put to it to distinguish clearly 

 between a catalytic and a non-catalytic process. 

 The so-called catalytic criteria are not really very 

 helpful. Ultimately the term "catalysis " will prob- 

 ably vanish from chemical literature as our know- 

 ledge of the mechanism of chemical processes 

 advances, though the term may remain for long 

 as a convenient, though arbitrary, term of classi- 

 fication. But we are very far from this state of 

 affairs at present, and there is the greatest pos- 

 sible need that the importance of the suljject 

 should be emphasised and its immense possibili- 

 ties clearly indicated. We find this well brought 



