332 SCIENCE PROGRESS 



Questions of sovereignty of the air, frontiers, difference in the laws of 

 various lands, registration of machine, efficiency of the pilot (including 

 medical examination), difference between crimes and torts as applied to the 

 air, customs, collisions and wrecks, are all discussed in a most impartial 

 manner — but the author does not fail to give a lead where one seems desir- 

 able. 



Notwithstanding the Convention relating to International Air Naviga- 

 tion in 1919 (full details and findings of which are given in Appendix I), 

 the author clearly shows the necessity for continued international activities 

 on the part of each and every Government. 



The possibilities of an Englishman flying a German machine from Belgium 

 to England and coming to grief, with damage to property, in France, are, 

 at the moment, truly Gilbertian. 



An excellent bibliography adds greatly to the volume, and while, as 

 already indicated, it is of particular value to lawyers, it could be and should 

 be read by all interested in aircraft. 



J. Wemyss Anderson. 



Aviation. By Benjamin M. Carmina. [Pp. xii + 172, with 92 figures.] 

 (New York: The Macmillan Company, 1919. Price us. net.) 



The author of this interesting little book is Assistant Chief Instructor at 

 the Y.M.C.A. Airplane Mechanics' School, somewhere in the United States of 

 America. It should be of great value to air artificers and mechanics, and 

 to those who wish to know something of the general principles of flight and 

 of the construction of aeroplanes, without the aid of mathematics. 



J. Wemyss Anderson. 



A Primer of Air Navigation. By H. E. Wimperis, M.A., late Major R.A.F., 

 Head of Air Navigation Research Section, Air Ministry. [Pp. xiv + 

 128, with 57 figures.] (London : Constable & Co., 1920. Price 

 85. 6d. net.) 



This volume is an elementary treatise on a subject of rapidly growing im- 

 portance, by an acknowledged authority on the subject. Whilst the funda- 

 mental principles of air navigation are the same as those of sea navigation, 

 the differences in detail are sufficiently great to render a separate treatment 

 of the methods of air navigation desirable. The two chief differences are : 

 (i) Observations are more difficult to make in an aeroplane than on a ship, 

 owing to the absence of a horizon ; (ii) the reduction of the observations is 

 simpler in air navigation, as the position of the aeroplane does not require 

 to be known with the accuracy required for a ship at sea. As regards the 

 first difference, it is true that a cloud horizon may sometimes be utilised, 

 but unless the cloud layer is at a uniform height, the results so obtained 

 are liable to a considerable error, even if the precaution has been taken to 

 verify that the dip of the horizon is the same at two diametrically opposite 

 points. This necessitates measuring true altitudes, and not altitudes above 

 the apparent horizon. The difficulty of determining the true vertical in 

 an aeroplane here enters, owing to the acceleration of the plane combining 

 with gravity to produce a false vertical. The disturbing effects of accelera- 

 tion are best avoided by using a bubble sextant, but in order to obtain reli- 

 able results, the plane must be flown as steadily as possible in a fixed 

 direction during the observations. It requires a very skilled pilot to do 

 this. The author has not laid sufficient emphasis upon this fundamental 

 fact. 



As regards the second difference, the range of vision from an aeroplane 

 being much greater than from a ship, and dangers from rocks and shoals 



