Notices respecting New Books. 299 



which does not differ more than +025 per cent, from 1*113 

 or Pill volt, according as amalgamated or electro-copper is 

 used; but such a cell cannot be kept many hours without 

 altering in value materially, and is in practice a very far less 

 convenient standard than the mecurous-sulphate cell of 

 Latimer Clark ; for, notwithstanding that the limits of varia- 

 tion between two cells of this latter kind, similarly prepared, 

 are somewhat greater than those of the best form of standard 

 Daniell cell, it nevertheless possesses the valuable property of 

 remaining sensibly constant (the temperature being the same) 

 for many months, and even one or more years, as will be 

 more completely shown in a future paper. 



XXXIV. Notices respecting New Boohs. 



RoorTcee Hydraulic Experiments. By Captain Allans' CtnonwgHAM, 

 B.E. Vol. I., Text pp. 399+xvi.* Vol. II., Tables— (1) Detailed 

 Tables, (2) Abstract Tables, pp. 156 + xii; pp. 49. Vol. III., 

 Plates, hi. Eoorkee : Thoniason College Press, 1880, 1881. 

 riTKESE volumes give an account of experiments, on Plow of 

 JL Water in a Canal, which lasted about four years (December 

 1871 to March 1879, with some intermissions). "We can hardly be 

 expected to go through this mass of calculation, but will endeavour 

 to put our readers en rapport with the results arrived at by Captain 

 Cunningham in his valuable labours, as here carefully digested and 

 served up for all whom they may concern. The mode of perform- 

 ing each experiment is given in great detail, not by any means a fault 

 in investigations of this nature. In condescension, however, to the 

 weakness of that bugbear, the general reader, a brief preface, or 

 resume of contents is attached to each chapter, giving "the gist of 

 the chapter without experimental or argumentative detail.'"' What- 

 ever data or residts appear to the author to be doubtful are indi- 

 cated by a query (?) attached. Elver-experiments on a small scale 

 are we'll known not to be applicable to large bodies of water. 

 India, with its many large canals, affords favourable opportunities 

 for such experiments, as our author observes, " with a fair expecta- 

 tion of a practically useful result."' 



The objects contemplated by Captain Cunningham were shortly 

 these : — (1) discovery of a good method of discharge-measurement ; 

 (2) testing the applicability of known mean-velocity formulae ; (3) 

 discovery of a good approximation to mean velocity : all three for 

 large canals . The main results which are stated to have been arrived 

 at are : — Loaded tube-rods give a rapid and sufficiently close approxi- 

 mation to mean velocity past a vertical ; with good arrangements 

 discharge-measurements obtained by the method advocated under 

 similar conditions may be expected not to differ more than 3 per 

 cent. ; none of the known mean-velocity formulae appear to be of 

 really general applicability ; central mean velocity-measurement 



