210 THE POPULAR SCIENCE MONTHLY. 



Coal has now receded in England to the old minimum price of 4s. 

 Qd. at the pit's mouth. Some of our northern railways are paying 6s. 

 a ton for coal. The price of the best Wall's End coal delivered at 

 private residences in London, at the end of January, 1879, was 29s. 

 per ton. Thus, even in the three hundred miles which divide the me- 

 tropolis from the pit's mouth, it will he seen that the price of coal is so 

 regulated by local conditions, and distance from the collieries, that it is 

 not easy to strike an average. We may therefore assume a price, 

 equal to that of petroleum, of 10s. per ton, for the sake of comparison, 

 and it will then be easy to apply the correction due to the price of coal 

 in any particular spot. The undetermined charges for interest on capi- 

 tal, merchants' profits, and delivery to consumers, may also be roundly 

 taken, for the sake of comparison, as equal for the diiferent materials. 



The cost of the manufacture and distribution of gas in London 

 (exclusive of the cost of coal) is about twenty per cent, over the amount 

 realized for the sale of the residual products of distillation, of course 

 excluding the gas. 10,000 cubic feet of gas per ton is a high, though 

 not the highest, production. The price of the residual products, as a 

 rule, is - so far regulated by the price of coal at the spot, that it is usu- 

 ally reckoned that the local price of gas in England is nearly inde- 

 pendent of the local variation in the price of coal, sales balancing pur- 

 chases. Thus, if we take 10,000 cubic feet of gas as costing the same 

 as one ton of coal, we shall be within twenty or twenty-five per cent, 

 of exactitude, as a general rule. We have, then, to compare the lumi- 

 niferous and calorific value of a ton of coal, a ton of petroleum, and 

 10,000 feet of cubic gas, assuming the approximate price of each of 

 these quantities to be equal. 



For lighting purposes, indeed, coal is nowhere. It has been occa- 

 sionally used for giving light on public works, such as railways, when 

 it was necessary to carry them on by night. But the light of a "devil," 

 or iron basket of live coals, is fitful and costly. As recently as 1815 

 the dangerous Bell Rock, at the entrance to the Firth of Tay, was 

 lighted by a fire-basket, or " chauffer," of live coals. It is stated in 

 the "Life of Robert Stevenson," the great lighthouse engineer, that 

 the consumption of coal in this " chauffer " was four hundred tons per 

 annum, while the light was never reliable when most required. In 

 violent gales the coal never burned on the windward side of the fire ; 

 and the guardian actually laid hold of the bars of the " chauffer," on 

 the windward, to steady himself Avhile putting on more fuel. Thus, in 

 the direction where, and at the time when, the light was most required, 

 it was all but totally invisible. The gas requisite to maintain a light 

 equal to one hundred Carcel burners, or nine hundred and sixty candles, 

 for twelve hours, is producible from half a ton of coal, as distilled in 

 the gas-works. This would yield a splendid light (if the locality were 

 such as to allow of its introduction) ; while the consumption of twenty- 

 two hundred weight per night of coal only made darkness visible. 



