kilogrammes (321-507 lbs. troy) of ordinary oil. These numbers are eloquent: they should, if not dispel, at least weaken the serious fears entertained by some, in consequence of the rapid exhaustion of coal-mines, and the necessity of going to increasingly greater depths, disputing with the subterranean water this precious combustible. The intensity of the calorific radiation of the sun is, moreover, much less at Paris than in intertropical regions, or upon the elevated plains. It is, therefore, probable, that the invention of "sunreceivers" will, some day, enable industry to establish works in the desert, where the sky remains very clear for a long time, just as the hydraulic engines have enabled them to be established by the side of water courses.

Although I have not been able to operate under very favourable circumstances, since my experiments have only been made with the sun of Alençon, Tours, and Paris, I proved, as far back as 1861, the possibility of maintaining a hot-air engine in motion, with the help of the sun's rays. More lately, I have succeeded in boiling, tolerably quickly, several litres of water submitted to insolation. In short, having satisfied myself that it was sufficient to have a silver reflector, with a surface of one square metre, to vaporize, in a hundred minutes, one litre of water (0.880 quarts), taken at the ordinary temperature, or, in other words, to produce seventeen litres of vapour a minute, I tried to work a small steam-engine by solar heat, and my efforts were crowned with success in June, 1866. In the meantime, I have been able, by very simple apparatus, to obtain some remarkable effects from insolation, such as the distillation of alcohol, the fusion of sulphur, perfect cooking of meat, bread, etc. None of these experiments, particularly the application of the sun's heat to machinery, have been tried upon a sufficiently large scale. It would, therefore, be useful to repeat them in tropical countries, with "sun-receivers" of suitable dimensions. We could measure the volume and the tension of steam produced in an hour by a given insolated surface, the pressure developed by the sun in a considerable mass of confined air, and the temperature which might be obtained by vast reflectors, formed of a framework of wood covered with plates of silver, etc.

COLOURED SPARKS AND THEIR SPECTRA.

M. BECQUEREL describes, in his treatise on light, "La Lumière et ses Effets," some elegant experiments, with an induction coil, which many of our readers will like to repeat. He takes a glass tube, about an inch in diameter, and five or six inches long, with a platina wire fused into its lower end, which is closed. This tube is halffilled with a solution of any of the substances which are able to give a vivid colour to luminous flames. In the top of the tube, a cork is inserted, through which a capillary glass tube is thrust, carrying a platina wire, which is allowed to project a trifle beyond its extremity, and to reach within a few millimetres of the surface of the liquid. When the apparatus is so arranged, strong sparks are sent through it by an induction coil. The distance between the platina wire carried by the capillary tube, and the liquid must, of course, be regulated by the length of spark the coil will give.

When the liquid is pure water, the discharges have a very pale colour; but if the water holds, in solution, small quantities of a salt, easily vaporisable, such as chloride of sodium, calcium, etc., they become brilliant with different tints. If the induction coil is weak, no colouring effect is seen when the upper wire is made the negative pole, it must then be positive. But if the coil is powerful, the colouring action is seen, whatever be the direction of the current, and the aureole surrounding it also exhibits coloured effects. The maximum of colour, however, always occurs, when the upper wire is positive. This result is contrary to what might have been supposed, for we know that the transport of matter in the voltaic arc, as in liquids traversed by electricity is from the positive to the negative pole. It is probable, in this case, that a polar decomposition takes place at the surface of the liquid, which gives rise to a reduction of the metal, and colours the discharge. With a coil of sufficient power, the effects are exceedingly brilliant.

The composition of the light thus obtained, is found, when examined by the spectroscope, to be more complicated than when similar salts are introduced into a non-luminous gas-flame, and a greater number of luminous bands are seen. Part of the water is vaporized, and we have the rays of its components, as well as those which result from the solution of the salt. The temperature afforded by the electric spark, is likewise higher than that of the gas-flame. The lines which arise from the volatilization of the platina must be

very weak, for, with the water, I have not been able to distinguish them. With other metals it may not be the same.

When concentrated solutions are employed, the luminous effects are very striking, especially when chlorides are used. The discharges are of a splendid red, with chloride of strontium; orange, with chloride of calcium; yellow, with chloride of sodium; green, with chloride of magnesium; bluish green, with chloride of copper; and blue, with chloride of zinc. Other salts, such as divers compounds of barium, potassium, antimony, iron, manganese, silver, uranium, etc., also produce effects equally well-marked.

The apparatus should be arranged, so that the discharges may succeed each other rapidly, and the phenomena may appear continuous. They thus resemble a coloured flame, and the tube acts like a little lamp, with a luminous source of definite composition, and affording a definite tint. To avoid trouble, through the heat occasioned, larger tubes may be employed, or capsules substituted.

If the bottom wire of one tube is made to communicate with the top one of another, and so in succession; several tubes may be employed at once, and their appearances contrasted.

ARCHEOLOGIA.

OUR Yorkshire barrow-diggers have recently been at work among the TUMULI NEAR BRIDLINGTON, and rather long accounts of their proceedings have appeared in the newspapers. Under the directions of Canon Greenwell, so well known for his earnest labours in this field of research, two of what the archæologists of the prehistoric school call "long barrows," which they consider to have belonged to a distinct race of "long-headed" or dolicho-cephalic men, who lived in a remoter period than the brachy-cephalic or round-headed race. The peculiar characteristic of these "long-headed" Britons, according to the same archælogical school, was, that they eat one another-in fact, that they were confirmed cannibals. The roundheaded-race, who were more civilized, and eschewed cannibalism, came later into possession of the land, and took the barrows which the long-headed people had left behind them, and used them again for burial-places, so that we find long-headed and round-headed buried in the same grave. But when the roundheaded race made barrows for themselves, they always made them round, and the new theory is, that all long barrows belong to the long

headed men, though you may find the remains of round-headed men in them, and that all round barrows belong to round-headed men. We confess, we cannot quite understand why the shape of a man's grave should be regulated by that of his head. The characteristics, therefore, of the long barrows appear to be, long-heads and short or round-heads, of which the latter are assumed to be a later introduction, and with them you meet with human bones thrown confusedly together, which are assumed to be the remains of a feast of cannibals. The two barrows which have been recently opened in the neighbourhood of Bridlington were long ones, and we shall proceed to describe them as well as we can from the newspaper accounts, which were evidently written by some of those who assisted at the excavations. The discoveries hardly appear to us to be of the importance here attached to them. Both these barrows are in the neighbourhood of Rudstone, the first upon the Dotterill Park, on the estate of Lord Londesborough, the other on the estate of Mr. Creyke, of Rawcliffe.

The barrow in DOTTERILL PARK was 170 feet in length, with a breadth of 60 feet at the east end, and 45 feet at the west-it lay N.E. by E. by S.W. by W. It is described as containing twelve different interments, of which one only was long-headed, which is therefore assumed to have been the "primary burial," while all the rest "were those of the round-headed race, and were inserted burials." It was, at all events, a long-headed barrow, filled with round-headed interments, with one only exception. The bodies belonged to men, women, and children. "With one body was a very peculiarly formed (bowl shaped) urn, but the barrow yielded very little pottery, and but few flints." The bowl, of a dark, plain ware, was with the long-headed body. The last burial but one towards the west had with it a "food vessel," with four pierced ears, which is described as very beautifully ornamented. The last burial in order, which lay in the western extremity of the barrow, was that of a young person, and was accompanied by an urn without any ornamentation except pairs of dots at intervals on the ridges. It is added that "from the appearance of this part of the barrow (in section) it seemed as if a later round barrow had been placed at the west end of the long barrow, and in the centre of this addition the last named burial had been made.

The barrow at RAWCLIFFE was 210 feet long, by 45 feet broad at the west, and 75 at the east end. Many little peculiarities were observed in the constructing of this barrow, and in the throwing together of its contents, which appear to us to be of very secondary importance, but the interments, of which a very small number were traced, in

comparison of the size of the barrow, were pronounced to be all longheaded, and no traces of what they call secondary interments were detected in it. But in the mass of the barrow were found "many broken up bodies, of which it was impossible to form any other opinion than that the disjointing had occurred at the time of death, and pointed to the disgraceful practice of cannibalism. The bones were scattered in strange confusion, and the skulls detached were found at some distance. An extraordinary amount of burning had occurred at the eastern end, as if the funeral feast had there been observed." These skulls are all pronounced to be long-headed. Thus the long-heads eat one another, and not the round-heads, or another race, or, in other words, they devoured their friends and not their enemies. It is added that "slightly buried at the extreme end, a very large number of fragments of Anglo-Saxon pottery was found, but they occurred in no other part." We think this may be an error, or the age of the barrow itself may have been mistaken.

The account of these excavations suggest more than one subject for remark. This new school of antiquaries have adopted the very erroneous system of studying the science downwards instead of upwards; that is, instead of first making themselves well acquainted with the archæology of the known period, and employing it backwards to assist in explaining that which is less known or unknown, they begin with the unknown period and expect it to explain itself, or to submit to their theoretical explanations, while they neglect the known periods altogether. The consequence of this may be easily imagined by those who study science on a wider scale. In the present case our investigators seem to imagine that it was quite a natural thing for a new race, which had driven a different race away from the soil, or had come into the vacant space they had left, to take possession of their sepulchral barrows, and adopt them as their own. Now this was not the case, and for a very good reason. The grave-the barrow-was a sacred place, consecrated to and believed to be held for ever by the spirits of the departed, who were further believed to defend their rights with a jealous energy against all intruders if they were not of their own family or friends, and especially against people of another race. They even, according to the popular belief, employed dragons and spiritual beings of a ferocious character, to brood and watch over their defence. The spirits of those who were buried in them, who spent their days in the national heaven-the Teutons called theirs Walhalla-returned at night to prowl about their barrows, and see that they were not intruded upon. So powerful were these protectors of the barrows, that the mythic