1855.] Mr. Dickinson on the Supply of Water for London. 47 



sian defences opposed a length little short of four miles, mounting 

 800 guns to the 500 of the combined armies, and aided by a gar- 

 rison whose numbers were unknown and capable of continual 

 augmentation. Screened from enfilade and ricochet fire by the 

 nature and length of their works, and by the difficulty of placing 

 the guns of the allies in favourable positions, the enemy could only 

 be assailed by direct or vertical fire ; and the troops rushfng to 

 the assault would have to advance to the attack over ground more 

 or less open and unprotected, after leaving the shelter of their 

 trenches. 



[E. J.] 



WEEKLY EVENING MEETING, 

 Friday, February 23. 



The Rev. John Barlow, M.A. F.R.S. Vice-President and 

 Secretary, in the Chair. 



John Dickinson, Esq. F.R.S. F.G.S. M.R.I. 

 On providing an Additional Supply of Pure Water for London, 



Mr. Dickinson commenced by describing the two different modes 

 of supply of water to towns, namely, the one by forcing it, by means 

 of pumping engines, directly into the pipes of supply called mains ; 

 the other by the delivery of it from a lake or reservoir on a high 

 level, also through pipes ; in which latter case the water, by l^e 

 mere force of gravity, will flow over large districts, and by the 

 comparative difference of level will rise to the tops of houses below 

 it, to which it is conveyed by the service pipes. 



He observed, that the supply by the New River Company com- 

 prehended both those modes. The river flowed into a reservoir at 

 Islington, called the New River Head, and, of course, mains, de- 

 riving their supply from that, conveyed water to a large district of 

 London situated below it ; but, furthermore, there were pumping 

 engines at that spot, which forced up water to reservoirs at High- 

 gate Hill and other places, from which it was supplied to districts 

 situated above the level of the New River Head. 



He observed, that in speaking of a natural supply of water col- 

 lected into a reservoir, at a high level, and delivered therefrom 

 without the aid of pumping engines, the technical expression of 

 engineers now is, " a supply by gravitation ; " and this is the mode 

 adopted wherever opportunity offers ; which is more rare in 



