. [ 661 ] 



LXVII. On a New Form of Catenary. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, — 



MAY I be permitted to point out that the theoretical 

 problem, which is dealt with by Capt. Hollingworth 

 in the October number of the Philosophical Magazine, 

 " On a New Form of Catenary," is solved on exactly the 

 same lines in a Report of mine, which was communicated to 

 the Advisory Committee for Aeronautics in October 1918. 

 Printed copies of this Report, entitled " On the Action of 

 Wind on Flexible Cables, with Applications to Cables towed 

 below Aeroplanes, and to Balloon Cables " (No. 554. Reports 

 and Memoranda, Advisory Committee for Aeronautics) may 

 be purchased at H.M. Stationery Office. With a simple 

 change of notation, Capt. Hollingworth's solution is iden- 

 tical with that in my paper, which contains also a discussion 

 of the forms the curve of the cable may take. The approxi- 

 mation which Capt. Hollingworth deals with is simply 

 obtained from my formulae by writing p, small [/a is the same 

 as p~}. 



In my paper, numerical results are given only for the 

 balloon cable, but some were considered for the towed cable, 

 as a preliminary to special experiments which were carried 

 out atOrfordness with moderately heavy steel cables. These 

 cables were calculated to lie at a steeper slope than those 

 considered by Capt. Hollingworth, and came under the 

 special case, considered in the paper, in which the inte- 

 gration is simply performed. 



Yours faithfully, 

 Gonville and Caiua College, A. R. M c Le0D. 



Cambridge, 

 Oct. 9th, 1919. 



LXVII I. Notices respecting New Books. 



Applied Optics : The Computation of Optical Systems. (Steinheil 

 and Voit.) Translated and edited by J. W. French, B.Sc. 

 Volume II. Blackie & Son. 



r piIE second volume of 'Applied Optics' presents a compre- 

 -*- hensive account of the determination of refractive indices 

 and dispersion, the computation of achromatic prisms and 

 doublet objectives, and discussion of the corrections for spherical 

 aberration. Two papers on " The refractive and dispersive powers 

 of various media " and " Trigonometrical formulae for 1 he refraction 

 Phil. Mag. S. 6. Vol. 38. No. 227. Nov. 1919. 2 Z 



