126 Scientific Intelligence. 



direction of its axis of rotation but also when this axis is displaced 

 parallel to itself by imparting momentum to the rotating system 

 by means of a foreign body." The fact that the latter pheno- 

 menon is not observed with gyroscopic apparatus is explained on 

 the ground of frictional resistance at the axle bearings. The 

 second part of the text (pages 24-44) relates to practical ballistics 

 and the author's interpretation of air resistance. Since the argu- 

 ments advanced are not formulated mathematically but are rather 

 long and controversial, it is difficult to find out just how far the 

 contentions of Dahne are correct without making a very exhaus- 

 tive and time consuming study of the text. Nevertheless, the 

 consequences of the author's " theory," as applied to the recorded 

 behavior of large projectiles, agree qualitatively and without 

 exception with the results of observation. Furthermore, it is 

 only fair to state that the monograph contains much food for 

 thought and hence it should be useful in suggesting lines of 

 further investigation. h. s. u. 



8. Text Book on Wireless Telegraphy ; by Rupert Stanley. 

 Pp. xii, 344, with 202 figures. London, 1914 (Longmans, Green 

 and Co.). — This book is intended to meet the needs not only of 

 students who have had no preliminary practice with wireless 

 apparatus, and who are taking up the subject for the first time, 

 but also of experts in ordinary manipulation who do not fully 

 understand the underlying theory of the appliances employed and 

 the phenomena involved. " The electron theory has been used ; 

 on it has been based all theoretical considerations, the author 

 believing that this theory, modern, simple, direct, and well estab- 

 lished, will present fewer difficulties to the student than the vague 

 fluid theories which it has replaced." That the field is covered in 

 a thorough manner may be seen from the following list of the 

 headings of the several chapters, namely : — "The Earth, the 

 Atmosphere and the Ether. Matter and Electrons. Magnetism 

 and Magnetic Strains in the Ether. Electricity and Electric 

 Strain in the Ether. Electrical Measurements and Calculations. 

 Capacity and Induction Effects. Induction Coils, Alternators, 

 and Transformers. Oscillatory Discharges. Historic Develop- 

 ment of Radio-telegraphy. How Ether Waves are propagated 

 and received. Coupling of Circuits. Transmitter Circuits for 

 Spark Systems. Transmitting Apparatus. Aerials, Insulators 

 and Earth Connections. Receiver Circuits. Detectors. Receiv- 

 ing Circuit Apparatus. Undamped Wave Systems. Miscella- 

 neous Apparatus. Measurements in Radio-telegraphy." 



The author's explanations are full and clear, the diagrams and 

 half-tone figures are excellent, and the book contains much useful, 

 up to date information. Most of the chapters end with a list of 

 questions and numerical exercises (171 in all) to be solved by the 

 student. Four appendices on codes and signals precede the 

 index. From the practical standpoint the text is quite accurate. 

 There exist, however, a few minor slips such as " Wein " for 

 W r ien, and "... X rays, discovered by Sir. Wm. Crookes." 



h. s. IT. 



