Notices respecting New Books. 165 



acceptable, to give the elementary theory of Flight on the simplest 

 assumptions, of flat plane wings, and the simple sine law for lift, 

 based on the quadratic law for normal incidence. The accom- 

 panying corresponding lines of lilt and drag could find a place on 

 the diagrams here of actual experiment, to show the extent of 

 divergence, and how slight this may prove. 



The standard law assumed in the treatise for normal air resistance 

 at a speed of V, f/s, is taken at 0-00237 V 2 , lb/ft 2 , and then this 

 is multiplied by a coefficient, Ki or Kd, to obtain the lift and 



drag. This law would appeal better if written 23*7 ( vjvr.) > lb/ft 2 , 



meaning that the resistance is 23*7 lb/ft" at a normal velocity of 

 1U0, f/s ; either as measured directly in a wind channel, or 

 inferred on the quadratic law from measurement at any other 

 velocity. 



There would be no need then for any mention of air density, or 

 explanation of the dreadful confusion of poundal and slug: send 

 them both to oblivion, to join spoucls, celoes, boles, and all such 

 dynamical Esperanto- Volapuk, superseded today by the rational 

 Hospitalier system, keeping the units and dimensions always in 

 sight. 



Weighing the Air was a favourite experiment in the early 

 days of the Royal Society, in which Charles II took a great 

 interest. 



But no measurement of air density is ever made in an aero- 

 nautical workshop, but the air thrust is measured directly, and 

 the speed of the air current. The solecism of lbs should not be 

 allowed to appear under official sanction as abbreviation of pounds ; 

 lb is short for the Latin word libra, plural librae. 



Applied Aerodynamics is a book indispensable to the constructor 

 and lecturer instructor, prepared by an authority with access to all 

 official information known on the subject, and a pioneer himself in 

 theoretical development. 



But not a book for the pilot to take up into the air, to consult 

 for the reason of every step ; as counselled by a well-known 

 authority on the teaching of Arithmetic. Intrepid on his bicycle 

 it is not the advice he would give a no\ice, but rather to let 

 himself go by pure instinct, and inconsiderately by reflex action. 



The Theory of Determinants in the historical order of development. 

 By Sir Thomas Mtjib. Vol. III. The period 1861-1880. 

 Macmillau &• Co. 1920. 500 pages. 



In the two previous volumes, vol. I carries the theory of general 

 and special determinants up to 1841; and vol. 11 covers the 

 period 1841 to 1860. 



The work is an obvious labour of love, and to be completed in a 

 fourth volume. It will prove a handbook indispensable to the 

 mathematician who has occasion to pursue this branch of Pure 

 Analysis. 



