Proceedings of Learned Societies. 223 



all our manufacturing wealth, was seriously considered. The facts 

 that, theoretically, a pound of coal is, by its combustion, capable of 

 producing sufficient mechanical energy to raise ten million of pounds 

 one foot high — that in our best constructed steam-engines only one- 

 tenth of that result is obtained — and that with our ordinary engines 

 not even one-third of this lower amount is produced, were carefully 

 considered ; and the inference drawn that in our average steam- 

 engines thirty times as much fuel is required as would be requisite 

 with a perfectly-constructed heat-engine. 



The possible substitution of some new source of motive power 

 was considered ; the fact that we cannot obtain mechanical energy 

 without the consumption of materials demonstrated ; and that no 

 materials could possibly be so cheap as the coal from the earth and 

 the oxygen of the air ; the latter costing nothing, and every pound 

 of coal rendering available two and a-half pounds of oxygen as a 

 source of power. The reason that the materials of water cannot be 

 regarded as a source of power is that the oxygen and hydrogen are 

 already chemically combined, and require the expenditure of a great 

 amount of chemical energy to effect their separation. 



The time when we shall utilize the natural falls of water as 

 sources of mechanical energy was regarded as inevitably, though 

 slowly, approaching ; and one great river was stated to develope at 

 a single plunge sufficient power to carry on all the manufacturing 

 operations of mankind, if they could be concentrated in its immediate 

 neighbourhood. 



The waste of coal in our ordinary households was a subject of 

 regret. In warming by open fires we consume at least five times 

 the amount of fuel requisite in a well-constructed stove ; and as 

 one pound of coal in an efficient steam-boiler is capable of evapo- 

 rating one gallon or ten pounds of water, the amount of fuel 

 wasted in our ordinary fires may be readily inferred. 



The increase of temperature below the earth's surface, as 

 measured at the Monkwearmouth colliery to a depth of 1800 feet, 

 was stated to agree closely with that observed in other localities, 

 namely, to be one degree Fahrenheit for every 60 feet. This, 

 assuming the fusing point of subterranean minerals to be 3000°, 

 would give a thickness to the earth's crust of about 34 miles, and 

 would from the mere increase of temperature prevent the working 

 of mines to as great a depth as 4000 feet. 



In connection with the dynamical theory of heat, the circum- 

 stance that every degree of heat (Fahrenheit) in one pound of water 

 is equivalent to 772 pounds lifted one foot high was stated, and also 

 that these amounts of heat and power were reciprocally convertible 

 into one another. This led to the consideration of the explosive 

 force of gunpowder, which first appears as heat and then takes the 

 form of mechanical power, communicated chiefly to the shot ; which 

 force is reconverted into heat when the motion of the shot is 

 arrested in striking an object. 



After alluding to the resolutions of Mr. Tyndall on radiant heat, 

 which have been described in our previous volumes, Sir W. Arm- 

 strong advocated strongly the introduction of the metric system of 



