rapid than before. The best test we have is that of the deepest coal pit in Great Britain, viz., that at Rosebridge near Wigan, where the shaft is now 2,376 feet deep, and is still descending lower and lower. There the ratio of heat-increase agreed with the ordinary rate down to a depth of 1,800 feet, after which it became considerably more rapid. At the lowest point of the sinking the thermometer indicated 92° Fahr.

Much more is said about temperature, and its equality and diversity, but the few foregoing and following facts are enough to enable us to understand the conclusions in relation to it. What is the maximum temperature of air compatible with the healthful exercise of human mining labour? Now the normal heat of our blood is 98°, and fever heat commences at 100°, and the extreme limit of fever heat may be taken at 112°. Dr. Thudicum, a physician who has specially investigated this subject, has concluded from experiments on his own body at high temperatures, that at a heat of 140° no work whatever could be carried on, and that at a temperature of from 130° to 140° only a very small amount of labour, and that at short periods, was practicable; and further, that human labour, daily and during ordinary periods, is limited by 100° of temperature as a fixed point, and then the air must be dry; for in moist air he did not think men could endure ordinary labour at a temperature exceeding 90°. Dr. Sanderson added useful testimony in detail leading to a similar conclusion, observing that gymnastic exercises can be practised by men in high temperatures up to a certain point, but that immediately when the temperature of the body rises to 102° or 103° Fahr., then all capacity for further exertion ceases. A case in Cornwall was instanced of the excavation of mining galleries where the air was heated by a hot spring to a temperature said to amount to 117°. Dr. Sanderson

visited this mine, and found the highest temperature to be 1141° Fahr., and the total duration of each of the men's work who were there engaged was less than three hours in the twenty-four. When urged to express the limit of temperature which he considered consistent with continuous healthy labour during five hours at a time, Dr. Sanderson replied, 90° Fahr., with the observation, that a man could not or would not do as much work in moist air at 90° as he could in ordinary conditions; and even at 90° the loss of working power would be very considerable.

The temperature of the earth at 3,000 feet deep would probably be 98° in England. Under what is technically called the long-wall system of working the coal, a difference of about 7° appears to exist between the temperature of the air and that of the strata at the working faces, and this difference increases 4 per cent. a further depth of 420 feet; so that the depth at which the temperature of the air would become, under present conditions, equal to the heat of the blood, would be about 3,420 feet. As to depths beyond this the Commission declined to speculate, but they thought that the ultimate limit of coal-working could be reached. Still many important details in the evidence on this question would, it appears to us, have to be reconsidered in all such deep coal-mining.

Besides the physical capacity of human endurance and existence at any such depths, the increased cost of working and winding up the coals, the greater wear and tear of materials as well as men, and the augmented difficulties of penetration and extraction, and of propping up roofs, would have to be considered, and would all tend to enhance the cost of coal, until perhaps such increased cost would bear such a large proportion to increased depth as to cause the financial to equal or exceed the mechanical obstacles. The deeper the pits

the larger the initial cost and the greater all subsequent expenses. If to win coal lying at a depth of, say 2,000 feet, costs 100,000l., to win coal at 4,000 feet might require 250,0007. Add to this that the rise in the cost of all mining materials has been as great as in other commodities, and we foresee limits financial and limits mechanical both combining against us; and where human free will, or rather ill will, superadds its opposing combination, it would hardly help us if half our earth were composed of coal or down to its centre while we could not use it.

Waste not, want not,' is a proverb as applicable to coal as in common life. We have wasted coal and therefore we do want it, and we have wasted in several ways, and to a most lamentable extent. Every one acquainted with coal-mining knows how much of this invaluable fuel has been absolutely and for ever lost by bad methods of working. It may be affirmed that during many years the amount of coal wasted by leaving pillars needlessly large to support the roof, by clumsy and quite unscientific methods of getting the coal, and by rough modes of carrying and delivering it, has amounted to fifty per cent. of the total; that is, that fully one-half as much coal has been wasted as has been delivered to the consumer.

It is melancholy also to learn that in what is termed the waste' and the 'goaves' of many large coal pits, some of which have been shut for ever, thousands upon thousands of tons of the best coal lie buried as in a fathomless sepulchre. Improvements in mining in the North of England have allowed of a much less wasteful extraction there than previously; but taking all our coal fields together, the ordinary and unavoidable waste amounts to at least ten per cent. of their whole delivery, while the avoidable waste sometimes reaches thirty or forty per cent.'

1 One singular example of waste is that of the 'pit-heaps,' which are known to colliers. We ourselves were wont to look at these vast mounds of

Early miners in newly explored districts will naturally perform their work in a primitive manner, and hence we are not surprised to hear that similar wastefulness characterises the working of the coal fields of other countries. An American authority estimates the entire waste in the mining of the anthracite of Pennsylvania as fifty per cent. of the total extracted. This loss of mineral seems the more inexcusable as the greater part of the present delivery of anthracite is extracted from a single bed called the Mammoth Seam. That seam is now exhausted above water level, and is known to depreciate below. If the extraction should increase like our own, and augment, as it is said now to do, by about five per cent. per annum, and should double itself in twenty years, it is easy to foresee the imminent exhaustion of that immense coal seam at available depths.

Out of all the coal which we have been burning for centuries nothing is surer than this, that we have never obtained a quarter of its theoretical heating value. We have squandered our mineral fuel like prodigals, with no better excuse than that we were in part helpless in our prodigality. As we know that our steam boilers now consume scarcely half as much coal as they consumed ten years ago, and as the present calorific effect is only one-eighth of the coal actually consumed, what must have been the waste of coal retrospectively for many years! In fact we may be said to have been burning coal in small coal, which had by annual accumulations swelled into very considerable mounds, and to wonder at the fearful waste of fuel therein involved. Many years ago we stood upon an eminence at South Hetton, and looked over a vast area of these pit-heaps, which, in some instances, were burning away during the night. All the colliers had free access to these accumulations of small coal, and filled their scuttles as often as they pleased. Now, however, the just retribution has arrived. These neglected pit-heaps have become valuable and chargeable; and what had been recklessly wasted for half a century is now sought with money and the remnants are sold to eager purchasers.

systematic waste; even now our knowledge of the laws of heat, and the adaptations of mechanism, do not combine in our favour as we should expect from the rapid advances of practical science. Other countries have been and are more economical in the comsumption of coal in their boilers, and this, as well as the great cost of the fuel, should stimulate the inventiveness of our mechanical engineers. Some of them think that we cannot confidently anticipate immediate economy of fuel. They argue, that since we cannot transfer above one-eighth of the total into mechanical power, while the natural conditions remain the same, and the same materials are acted upon, we must not expect a future economy of more than two-sevenths, and that even this economy will probably only be effected in the next generation.

As the consumption of coal in iron works of all kinds consists of about one-fourth of our whole extraction, it would be highly desirable if a considerable economy could be effected in this department of industry. But we have little immediate hope of its realisation. We have said that Dank's rotary furnace is not expected to save much fuel, nor do other hoped-for improvements promise much more immediately. In other branches of metallurgy there is similar waste of coal, but there is little prospect of saving excepting in copper works, where economy is plainly possible.

Nearly every householder has been lately discussing, and often adopting, expedients for economising his costly fuel, and much has been written and said about grates and stoves, and bricks and iron plates, and fire-balls. Here again we want because we have wasted; we have all been using open grates, and these probably deliver to our apartments an amount of heat which may be represented as one-twentieth of the total heat capable of being extracted from the fuel they consume. When, however,