Geological Society. 383 



And Differentiation would be called the formation of the 

 differential equation, by the elimination of the constant. 



The author himself employs this idea in Chapter III, where he 



proposes the differential equation -=-; =y, or Tcy,n% the definition 



of the exponential function. In the associated graph the curve 

 has a constant subtangent. 



A feature of the treatment is the banishment of Taylor's 

 Theorem to the end of the book. This will prevent young Rigour 

 from keeping his class marking time ever so long over the Failure 

 of Taylor's Theorem, all he seems to care about. But the beginner 

 is delighted with the theorem when he finds it gathers up all the 

 preceding isolated expansions of his functions of a real variable 

 in a series, and gives him a method he can employ with suitable 

 precautions for the numerical calculation of his function, to any 

 desired accuracy. 



The Sublime Calculus was the former noble name of our subject, 

 replaced to-day by Infinitesimal. It is treated here with a view of 

 immediate application, as well as for the benefit of the mathe- 

 matician on his road to higher developments. Scores of lowly 

 treatises are in use, to minister to the immediate wants of the 

 engineer and electrician, with their presentation from the direct 

 commercial aspect. These all shirk such abstractions as the ideas 

 explained in Chapter I here. 



XXXVII. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from vol. xxxviiL p. 748.] 



November 5th, 1919.— Mr. Gr. W. Lamplugh, F.R.S., President, 

 in the Chair. 



A Lecture was delivered by Hugh Hamshaw Thomas, M.A., 

 F.G.S.. 'On some Features in the Topography and 

 Geological History of Palestine,' illustrated by aeroplane 

 photographs taken during the War. 



The Lecturer observed that a perfectly new method of illustrating 

 and investigating some branches of physical geology is afforded by 

 Aeroplane Photography. It seems firstly to illustrate in a very 

 striking and. convincing form many geological phenomena, such as 

 the structure of a volcano or the land-forms resulting from erosion, 

 and may be of value in the teaching of the science. In the second 



