SO TEAR-BOOK OF FACTS. 



bulator, which is simply a wheel 9 inches in diameter, centred in a 

 bar hinged to the fore axle of the vehicle, and spurred to it on both 

 sides, so that when the wheel revolves in the groove the axle is 

 always at right angles to the rails. This bar is suspended from the 

 splinter-bar by a strong elastic band, which holds the wheel about 4 

 or 5 inches clear of the road ; and an upright rod, passing through 

 the footboard, and acting on the perambulator, enables the driver, 

 when he has fairly adjusted his vehicle upon the rails, to depress, by 

 the action of his foot, the wheel into the groove of the centre rail, 

 and to retain it in position as long as he wishes to remain on the 

 metals. 



SUBWAYS FOR GAS AND WATER MAINS. 



Professor Spencer's Report to the New River Water-works 

 Company, on the corrosion of iron mains from the eti'eets of gas 

 leakage, basing the calculation on a gas waste of 20 per cent, (a 

 standard somewhat below the fact), after making a fair allowance 

 for probable waste from other causes than that of leakage, — such, 

 for instance, as defective meterage, condensation, &c, — estimates 

 the actual amount of loss from leakage through the joints of the gas 

 mains at 630,000,000, cubic feet per annum, all of which is absorbed 

 into the earth, imparting to the subsoil of the streets the blackened 

 appearance and odour so familiar to the in-dwellersof the metropolis. 



As respects the more immediate object of his employment in this 

 instance, viz., the cause of the premature decay of the iron mains 

 that takes place in some of the denser parts of the metropolis, Pro- 

 fessor Spencer — by careful observation, and a series of experiments 

 conducted through a period of three years — arrives at the conclusion 

 that such decay is caused by the gas that is always escaping from 

 the joints of the gas mains, not directly by the action of the gas itself 

 — for alone this is harmless in this way on the iron — but by an acrid 

 alkaline fluid, a sort of distillation, as it were, from the gas-charged 

 earth by means of moisture from the tain-fall ; which fluid, coming in 

 contact with the metal of the pipes, produces profuse corrosion, 

 having the effect of converting the iron, in a shorter or longer period, 

 into a sort of plumbago. Numerous specimens of decayed pipage 

 turned up during the progress of the inquiry, showing the action of 

 this destructive agent, so rapid in certain spots where more than 

 usual gas escape had been going on, as to effect that transition in the 

 short space of from seven to ten years; the ordinary serviceable 

 duration of iron similarly employed in earth in its natural state being 

 about a century. 



As respects the injuries sustained by the public from the chronic 

 escape of gas, Professor Spencer affirms, Bret, that the gae-satnrated 

 earth, in combination with certain other chemical properties, which 

 the London street subsoil imbibes from other causes, gives out a 

 sulphurous gaseous matter, which, inhaled, is highly prejudicial to 

 health ; and it is observed that, when it is taken into account that 

 each cubic foot of this enormous quantity of gas, which is con- 

 tinuously passing into the street earth, contains something like oue- 



