November 27, 1919] 



NATURE 



331 



Section of the United States Army. It gives an 

 accurate survey of the theory of electromagnetism 

 with special stress on its application to practical 

 radio-communication. Very little mathematical 

 knowledge is assumed on the part of the reader, 

 and the familiar analogies given will be a great 

 help to beginners. 



The first and second chapters give a clear 

 resume of elementary electricity and the working 

 ■of dynamos. In the third chapter radio-circuits 

 are described, stress being laid on coupled 

 circuits, oscillations, damping and effective resist- 

 ance. The fourth chapter describes electro- 

 magnetic waves, and the academic theorist will 

 be surprised at the simplicity and accuracy of the 

 transmission formulae used in practice. Descrip- 

 tions of the best types of antennas and of open 

 and closed coil aerials are also given. In chap. v. 

 the apparatus used in transmission and reception 

 is described, and it is carefully stated which is 

 -suitable for damped and which for undamped 

 waves. Chap, vi., the final chapter in the book, 

 will be very helpful to many, as it gives an excel- 

 lent account of the various types of vacuum tubes 

 now in use. By means of the characteristic curves 

 the working of the three-electrode tube is simply 

 explained. Its use as an amplifier, modulator, and 

 generator of oscillations is fully described. The 

 method of connecting vacuum tubes in cascade is 

 also given. 



Many fail to recognise how easy it is to detect 

 radio-waves, and how simple is the necessary 

 apparatus. For damped waves, all that is re- 

 quired is a telephone receiver, a rectifier (crystal 

 "detector," or, better, a vacuum tube), and a 

 tuning coil. It seems to us to be foolish for the 

 Post Office to keep up the comedy of pretending 

 to regulate the use of such sets. Now that the 

 licences to technical colleges have been formally 

 withdrawn it would be politic to issue new ones 

 without any further delay. 



The latest developments of radio-communication 

 make the subject of absorbing interest to the 

 engineer and the man of science. For instance, 

 the power involved in the sound-waves generated 

 in ordinary speech is of the order of the hundred- 

 millionth of a watt, and yet in radio-telephony 

 this controls several thousands of watts, the alter- 

 nating currents being at radio frequency. In the 

 pre-war days the use of crystal rectifiers intro- 

 duced an element of uncertainty into everyday 

 working. This was (^ercome by the Fleming 

 valve, which is now replaced by the three-elec- 

 trode vacuum tube. For measurement purposes 

 the vacuum tube is far superior to the " buzzer " 

 as a source of oscillations. If several tubes are 

 used in the same circuit, • and each tube has its 

 own battery, then the amplitude and frequency of 

 the current-waves can be made practically con- 

 stant. 



There are very many interesting and novel facts 

 given which will be of great value to the radio 

 engineer. The book can be heartily recommended 

 to every man of science who wishes to know the 

 latest practical developments. .\. R. 



NO. 2613, VOL. 104] 



ROUND THE WREKIN. 



Shropshire : The Geography of the County. By 

 Prof. W. W. Watts. Pp. x-i-254. (Shrews- 

 bury : Wilding and Son, Ltd., 1919.} Price 

 25. 6d. net. 



SHROPSHIRE, in its combination of moun- 

 tain and plain, in the varied flow- and 

 scenery of its river, for which the whole county 

 serves as catchment basin, in the extent of its 

 stratified rocks from pre-Cambrian to Lias, in 

 their yield of coal, building-stones, metals, and 

 workable clays, lends itself admirably to treat- 

 ment by a geographer who is also a geologist, 

 and it is needless to say that Prof. Watts, whose 

 geological studies of the county alone or in con- 

 junction with Prof. Lapworth have been a guide 

 to so many, avails himself thoroughly of the 

 opportunity. The rich and beautiful forests, the 

 meres, and the rocky uplands support a multiform 

 assemblage of birds. The more important among 

 these and other animals are noted, but it might 

 have been mentioned that a complete series of the 

 vertebrate fauna has been collected and placed on 

 exhibition by Mr. H. E. Forrest in the Shrews- 

 bury Museum. The diversified agriculture and 

 the numerous industries down to the making of 

 "churchwardens" are briefly correlated with 

 rocks and soil. 



But Prof. Watts recognises that the great 

 interest of Shropshire lies in its human inhabitants 

 and their history. Though Palaeolithic man has 

 left no trace in the county, his Neolithic suc- 

 cessors are known, not merely from their weapons, 

 stone circles, and barrows, but from their many 

 descendants in the present population. The 

 Brythons, who became the Cymry to themselves, 

 the Welsh to their enemies, are now represented 

 by about one-tenth of the inhabitants. Their 

 coracle is still used by Severn fishermen. It was 

 the struggle between them and the English com- 

 pound of Angles and Normans that so long made 

 Shrewsbury a city of prime importance. All this 

 eventful history and its relation to the physical 

 features is clearly summarised by Prof. Watts. 



The beautiful half-timbered houses of the 

 fifteenth, sixteenth, and seventeenth centuries are 

 famous, but such stone mansions as those of 

 Benthall and Condover, such castles as Stokesay, 

 Ludlow, and Shrewsbury, and the fine ecclesi- 

 astical architecture of Buildwas, Wenlock, Lud- 

 low, and Shrewsbury, receive description and 

 illustration so far as space admits. A chapter on 

 the place-names is of peculiar interest, and the 

 sections on communications and the origins of the 

 chief towns are excellent lessons in political geo- 

 graphy. Coloured physical and geological maps 

 form the end-papers of the book. 



There is an index, but it has not helped a re- 

 viewer fresh from his home-county to find the 

 explanation of "Meole," the meaning of the 

 "Weeping Cross," the origin of Bomer and 

 similar "pools," or any reference to the " Burries " 

 or Burgs of Bayston Hill. Farquhar's "Recruit- 

 ing Sergeant " might be worth a line. A Salopian 



