Nov. 1st, 18S7.] 



SCIENTIFIC NEWS. 



211 



It has to be borne in mind that a great increase in strength 

 was not the only advantage attending the substitution of iron, and 

 afterwards of steel, for wood in the construction of our ships. 

 The saving of weight, particularly when using the last mentioned 

 material, is such that it increases the capacity of the vessel 

 sufficiently to contain in the space gained more than coal enough 

 to take her across the Atlantic. It will be interesting to review, 

 however shortly, the other causes in addition to this which have 

 so entirely falsified the prediction of Dr. Lardner and others. In 

 the early years of the engines built by James Watt it was 

 deemed, no doubt principally on account of imperfect workman- 

 ship, inconsistent with safety to use a piston speed exceeding 220 

 feet per minute. In the case of marine engines, as well as others, 

 improved machine tools enabled our builders to obtain a much 

 higher velocity, but this was limited by the weight and dimen- 

 sions of the paddle wheels in large ocean-going steamships. 

 This impediment to progress was removed by the invention of 

 the screw which permits three times the rate of piston speed 

 laid down by Watt. To follow up this improvement a great 

 extension of boiler power was needed beyond that required by 

 this great engineer. The use of cast iron boilers, one of which 

 was working in my own time in Newcastle, and afterwards those 

 built up of small plates, sufficed for the low pressure steam 

 employed in his condensing engines. By more suitable iron 

 used in boilers of improved construction, steam was employed at 

 such a pressure that a vessel having a carrying capacity of 3,750 

 tons could land in New York a cargo, taken in at Liverpool, 

 weighing 3,000 tons. This was enough to enable her to cross 

 the Atlantic in 14 days with a consumption of 750 tons of coal. 



The capacity of steam as a propelling power depends of course 

 on volume and pressure, and hence on the temperature of that 

 passing through the cylinders. We all know how the dangers 

 attending the use of steam at a high pressure have been met by 

 the introduction of the compound system, in which, by the use 

 of three cylinders, a great addition to the e.xpansive force of the 

 steam is now very largely employed. To such an extent has 

 this been carried, that 350 tons of coal are now doing the work 

 which formerly required 750 tons, enabling such a vessel as I have 

 selected for illustration to carry 3,400 tons across the Atlantic, 

 instead of 3,000 as formerly. The application of very highly 

 heated steam has of course its limits, connected with the action 

 of heat on the oil, etc., used for lubrication, as well as that on 

 metallic surfaces themselves, when exposed to friction. Into 

 these questions of detail it is not however necessary here to 

 enter. 



If we go back 120 years, when steam power was beginning to 

 be applied to the drainage of our coal pits, the duty performed 

 was very low, namely, about 64,000 lbs. of water raised one foot 

 per lb. of coal burnt. The engines then used owed their motion 

 to the pressure of the atmosphere, steam being merely employed 

 to obtain a vacuum by its condensation, got by injecting cold 

 water into the c)'linder. James Watt effected the same end by 

 a separate condenser, and then proceeded, in addition, to work 

 his steam expansively, by which he raised the duty to 316,000 

 lbs. Gradually, by means of more highly-pressed steam and 

 better-constructed engines, the duty was increased to above 

 950,000 lbs. The researches of Black, the chemist, on latent 

 heat first directed the attention of Watt to separate condensa- 

 tion, which, with the observation of practical engineers of great 

 skill, constituted the only guides for improving the steam-engine, 

 until Joule's determination of the mechanical equivalent of heat 

 in 1843. By this distinguished physicist it was ascertained that 

 in burning a single pound of coal there was energy developed 

 equal to raise 11,422,000 lbs. one foot high, but that the actual 

 useful effect obtained from a steam-engine and good boilers did 

 not when he wrote exceed 1,000,000 lbs. raised one foot in 

 height, showing a loss of 91 '25 per cent, of the power of the 

 coal. This information to the engineer is invaluable, because it 

 enables him to realise the exact amount of his loss, and also 

 forms the key in looking for its cause. It was to avoid this 

 loss that Ericsen and others suggested and built engines to be 

 driven with heated air. The amount of pressure which can be 

 commanded, even at a temperature as high as 480° F. (177 C), 

 is, however, so small that the machinery for utilising it must 

 have unmanageable dimensions. 



Although the existence of coal in our immediate neighbour- 

 hood was known to the Romans, it may be estimated that one- 

 half of the entire output got from the field up to this time has 

 been worked during the last twenty-five years, so rapid has the 



recent increase of the demand on its resources been. Having 

 regard to its ascertained extent, unless its boundaries are en- 

 larged by some unexpected discoveries, which is more than 

 problematical, we or our successors must begin before long to 

 prepare for a diminished produce and increased cost. It is true 

 Dr. Lardner told us, forty years ago, to be under no apprehen- 

 sion in respect to our position when our national beds of coal 

 became exhausted ; for he assured us that the operations of 

 nature afford abundant hope of a substitute being found, elec- 

 tricity and hydrogen gas got from water, however, being the 

 only ones he specified. Mr. Mulhall repeats this opinion as 

 regards electricity in 1880,* alleging that this agent is already 

 supplying the place of coal. He seems, however, apparently to 

 disregard the fact that nearly in every case the electricity was 

 being obtained by burning coal under the boiler of a steam- 

 engine. Everyone who has bestowed a thought on the opera- 

 tions of nature, referred to by Dr. Lardner, knows the sun to be 

 the source to which they owe their existence. The potential 

 rays of this luminary continue, as they did in pre-historic ages, 

 to dissociate the elements of the carbonic acid of our atmosphere, 

 le.-iving their immeasurable energy transferred to the numberless 

 forms of vegetation which cover the face of the earth. The 

 same power creates currents of air and raises the water of the 

 ocean to the summits of mountains. Thus we have the heat 

 which split up carbonic acid into its elementary constituents ; 

 which rarified the air and evaporated the water, capable of being 

 returned to us in the form of motion ; or, if we choose, such 

 motion may be reconverted into heat by means of suitable 

 appliances. 



When, however, we set to work to consider the adaptation of 

 the operations of nature as they are taking place under our eyes, 

 we shall find that enormous periods of time or vast areas of 

 space are involved in their application. It has been estimated 

 that thousands of years were needed to produce the beds of 

 coal which were formed beneath the surface of this and the ad- 

 joining county. The charcoal capable of being grown in a year 

 on an acre of land would only suffice to propel one express 

 train over a distance of twenty-five miles ; and for making the 

 pig-iron annually produced in Great Britain a forest of 42,000 

 square miles would be required. As regards the movements in 

 our air, Jevons calculated that it would take 1,000 wind-mills to 

 drive a modern rail-mill. This would mean lines of these 

 engines extending over something like twenty miles, and all to 

 be connected with the fly-wheel shaft of the rolling machinery. 

 The collection of the rain which falls over a large area of 

 country into rivers affords, it is true, a ready means of concen- 

 trating its power at one point. The advantage thus placed at 

 our disposal is obtained at a sacrifice of that portion of the 

 force represented by the descent of the water from the 

 more elevated and often less extensive parts of the field 

 which is drained. Let us suppose that in order to secure 

 the necessary volume of water the barrier of interception is 

 placed fifty feet above the sea level at high tide. If we 

 assume the annual rainfall over the entire acre to be 3,000 

 tons, and none being lost by evaporation or otherwise, the whole 

 to fall over the height just referred to, we should have a yearly 

 mechanical force of 336,000,000 foot pounds. This, according 

 to Joule's investigations, after allowing 30 per cent, loss of 

 power for friction in a water wheel, would only represent 20'6 

 lbs. of coal ; but we have seen that in one way or another go 

 per cent, of the power of coal may escape in its application ; 

 hence, the 3,000 tons of water collected on an acre of land in 

 one year would, in falling from an altitude of 50 feet, afford in 

 available power, after deducting this loss of 90 per cent,, an 

 equivalent of that obtainable from 206 lbs. of coal burnt under 

 the conditions already described. It would be easy to calculate 

 the amount of energy capable of being derived from impound- 

 ing tidal water. The result, however, would only resemble, in 

 its general outlines, that afforded by the examples already 

 given. There are, it is true, certain cases in which the heat 

 required has to be generated under conditions where its cost 

 practically forms no element in the calculation. If, for example, 

 it is desired to despatch a mass of iron weighing 1,800 lbs. on a 

 journey of half-a-dozen miles, the terminus of which must be 

 reached in a few seconds, we must employ suitable means for 

 the instantaneous development of the necessary heat. For this 

 we need an Elswick gun for our furnace, costing it may be 

 _^20,ooo, and 960 lbs, of gunpowder for our fuel, costing /60 , 

 * " Progress of the World," p. 68. 



