applied a strong blast of air, which combines with the carbon at an intense white heat. This is continued for about eight or ten minutes, until the whole of the carbon is consumed, when the blast is stopped. In this stage a quantity of metal, containing the requisite percentage of carbon necessary to form the exact quality of the steel required, is poured into the vessel, and this combining with the refined iron gives to the mass all the properties and characteristics of steel.

To show the facility with which the crude iron may be converted into refined iron or steel, the converting vessel may be placed if necessary so near to the blast furnace as to allow the iron to flow direct into it; or the metal in the shape of pig-iron may be melted in reverberatory furnaces, as is now generally the case, and thence run direct into the converting vessel. This vessel is of the shape shown in the Plate, supported on trunnions at A, which enable it to turn upon its centre and discharge its contents into a large ladle when the process is complete. The general apparatus will, however, be better understood by referring to the Plate, which is a view of the interior of the converting house. It will be seen that two vessels, A A, are employed; they are placed in such a position as to throw the sparks and slag away from each other, and into the lower part of the chimneys, B B, which have hoods at B* to conduct the flame into them. The casting pit is semicircular in front, and central to it is placed the casting crane c, which supports the ladle into which the steel flows, and from which it is delivered through a cone valve, a, at the bottom of the ladle. One of the vessels is shown in section in the act of pouring out the fluid steel into the ladle, while in the other the process of conversion is going on. When necessary both vessels may be worked at the same time, and their contents poured into one large ladle, so that an ingot of 20 tons may be made from what is usually styled a 10-ton apparatus. It will be observed that the hydraulic casting crane, c, is brought so far from the line formed by passing through the centres of the converting vessels as to allow one vessel to be moved round if necessary, while the ladle is in front of the other vessel. This position of the crane enables the casting pit to be made larger, and gives more space for the moulds.

In the act of pouring the steel from the converter into the casting ladle, the crane is steadily lowered and its bend moved round to accommodate the curved path in which the spout of the converting vessel moves. This lowering of the crane is effected by a boy on the valve stand, which is situated at a distance of about twenty feet from the casting pit, and in a line with the centre of the casting crane. On this stand the cocks for the moving of the vessel are placed; here also are the handles of two large balanced air-valves by which the blast is regulated.

To ascertain the comparative values of steel when subjected to transverse, compressive, and tensile strains, the following abstracts of results have been taken from "Fairbairn's Experimental Researches on the mechanical properties of Steel in its present improved state of manufacture.

Abstract of Summary of Results from the Experiments on Transverse

In this short abstract we are unable to give the experiments in full or the General Summary of Results, our limited space admitting only the mean value of each sample of bars as received from the different works. These bars were of different qualities, and were tested separately in order to determine their tenacity, elasticity, ductility, &c., and the details of each are given separately in the general table of Results. From these tables we have merely taken the mean of the resistances to strain and the working values of the bars as determined from the experiments and the samples, taken collectively, from each marker. În the general report, the strength and other properties of the different specimens are given separately, and for these details we must refer the reader to the Transactions of the British Association' for 1867.

It will be observed that the above and the following tables of Results are taken from the General Summary, where the deflections, elongations, and compressions are carefully recorded; and from these are deduced the different powers of resistance and working value, as exhibited in the columns of each table. The difference in this case is, that the mean results are taken from the whole number of specimens received from each maker, and not from the separate bars experimented upon, as given in the Tables.

The first column gives the names of the makers, or the works from which the steel was obtained; the remaining columns give respectively the deflections for unity of pressure and section, the modulus of elasticity corresponding to 112 lbs. pressure, the work

of deflection and the unit of working strength, which is the mean value or working tenacity of each set of bars, as deduced from the experiments in their collective form.

Abstract of Summary of Results from the Experiments on Tension.

From the above it will be seen that the mean of all the specimens of steel experimented upon is greatly in excess of iron, which, taken at a breaking strain of 20 tons per square inch of section, gives a ratio of 43-46:20, or as 2.17 to 1, being more than double that of iron in its resistance to tension. These and previous experiments clearly show the advantages which this material has over iron in its malleable state, and the important benefits which it is likely to confer when rightly applied in constructive art.

Abstract of Summary of Results from the Experiments on Compression.

This table shows the resisting powers of steel to a force tending to crush it; the middle column exhibits the amount of compression produced by 100-7 tons, the mean of which is 315.

These experiments also indicate the superior resisting powers

of steel, which in every case is greatly superior to iron in all the varied forms of resistances to strain to which it may be subjected.

We have given this short abstract from a long series of recent experiments in anticipation of steel superseding iron in almost every case where strength is required. That the time is not far distant when this will be accomplished, we have every reason to believe, and assuming that the change will be of great national benefit, we shall hail with the liveliest satisfaction the disappearance of iron and the substitution of steel as a superior material for general purposes of construction.

III. ON EXPERIMENTS FOR ASCERTAINING THE
TEMPERATURE OF THE EARTH'S CRUST.
By EDWARD HULL, F.R.S.

THE question of the rate of increase of temperature of the Earth's crust from the surface downwards is one which engaged the attention of members of the British Association at the recent meeting in Dundee, and to the investigation of which, by actual experiment, the Association is likely to devote some portion of its funds. In anticipation of such operations, we venture to offer a few observations both as regards what has been done and what may be done and the mode of doing it, even at the risk of suggesting matters which have already occurred to the minds of those who are to carry out the experiments entrusted to them. It is desirable that whatever money and labour are to be devoted to this purpose should not be uselessly expended in the repetition of observations which have already been made with a degree of accuracy as great, perhaps, as the case admits of, but that they should be used in perfectly new and untried grounds, or, in other words, for the testing of hitherto unexplored depths. Before entering, however, upon this branch of our subject, we shall prepare the way by bringing to the reader's notice examples of what has already been done by previous investigators.

Although the opinions of philosophers regarding the condition of the internal nucleus of the globe are widely different, all are probably agreed as regards an actual increase of temperature from the surface downwards to an unknown depth; and that this is the fact the evidence both of a theoretical and experimental character is probably conclusive. It is no argument against this view that we find strata, in their natural or unaltered state, which on stratigraphical grounds we believe to have been at one time buried beneath newer strata to a depth of several thousand feet; for assuming the increase of heat to be at an average rate of 1° Fahr. for every 60

feet, the boiling point of water would not be reached under 12,720 feet; and while on the one hand it is doubtful whether metamorphism would take place in ordinary strata at this temperature, it is seldom we meet with rocks which we are certain had originally been buried at much greater depths.

Whether this increase of temperature is continuous for any considerable distance in reference to the semi-diameter of the earth, or whether it increases or diminishes according to definite laws, are questions which are probably beyond solution by actual experiment, for, in the words of Humboldt, the question of the internal central heat, as a mathematical problem," yields rather negative than positive results." The experimental evidences, however, as far as they come within the range of investigation, all point to one conclusion. They are also of several kinds, derived from observations of the temperature of the water springing from different depths through artesian borings-those obtained from testing the temperature of the water issuing from coal-seams and fissures in mines, and those obtained from observations made during the sinking of mining shafts both through wet and dry strata. It is on the experimental evidences we propose here to dwell, and taking some examples from authorities within our reach, to present the reader with a succinct account of what has already been achieved, and afterwards to offer some suggestions as to the best manner, in our opinion, for pursuing further investigations.

One of the most remarkable and carefully-observed cases of artesian borings is that of the Puits de Grenelle, near Paris. The sinking of this bore-hole was watched by Arago till 1840, down to a depth of 1,657 feet, when the borer had left the Chalk formation, and was beginning to penetrate the Gault. The series of observations were completed by Walferdin in 1847. The surface of the basin of the well at Grenelle lies at an elevation of 119 feet above the sea, and the borings extend to a depth of 1794-6 feet from the surface. The water which rises from the Lower Greensand formation is of a temperature of 81.95° Fahr., and the increase is at the rate of 1° Fahr. for every 59 feet.*

The next boring we shall describe is that of Neu Saltzwerk, in Westphalia, and situated 231 feet above the level of the sea at Amsterdam. It penetrated to an absolute depth of 2,281 feet from the surface. The salt-spring lies, therefore, at a depth of 2,052 feet below the level of the sea, a relative depth which is, perhaps, the greatest that has yet been reached. The temperature of the brine is 9104° Fahr., and as the mean annual temperature of the air at these works is about 49.3°, we may assume there is an increase of 1° Fahr. for every 54.68 feet.† This boring is 487 feet deeper

*Cosmos.' Trans. of Otté and Dallas, v 1. v., p. 35-6. + Ibid., p. 36-7.