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illumination depend were then referred to. Every method of artificial illumination depends upon the heating of certain bodies to such a temperature that they become incandescent With gases this temperature is much higher than with liquids or solids. There is only one instance in which the incandescence of vapour is used, and that is the mercurial electric light, already alluded to. In all other cases the incandescence of solid bodies is employed. In the ordinary method of obtaining the electric light, the incandescence of solid prisms of carbon is the source of luminosity. In gas and oil flames, it is the incandescence of little particles of carbon, and in all these cases the light is produced from solid matter. The luminosity of any flame depends, first, upon the number of solid particles which exist in it at any given moment; and, secondly, upon the temperature of the flame. The number of solid particles is dependent upon the nature of the flame itself, whether it be a flame produced by the burning of bodies rich in hydrocarbons, or by the burning of bodies which are poorer in this respect. Such a flame is always affected by the pressure of the atmosphere. The higher the pressure of the air, the greater the number of luminous particles of carbon present at one time in the flame. If, after the barometer has been standing at 30 inches, it falls to 29 inches, the light of all flames is reduced to the extent of about 5 per cent. The temperature, upon which the luminosity of a flame also depends, may be increased by heating both the gas and the air supplied to it for combustion, before they are brought together to be burned.

The speaker exhibited a gas lamp which he had constructed to effect this object. It consisted of an ordinary argand burner, with glass chimney, but furnished with an outer glass cylinder resting upon a solid plate of glass, through the centre of which the tube supplying the gas rose. Thus all the air supplied to the flame was compelled to pass down between the chimney and outer cylinder, becoming thereby strongly heated before it reached the flame, whilst considerable heat was also imparted to the gas before the latter issued from the burner. In this manner a great increase of light, with the same consumption of gas, was obtained.

The following table was exhibited, showing the effect of this hot air gas-burner in reducing the consumption of gas for a given amount of light, and thereby also the impurities and heat which are thrown into the atmosphere in which such a lamp is burned :

Rate of consump Illuminating
tion per hour.

power.
Argand burner sup-

3.3 cubic feet 13 sperm candles,
307

15.5
plied with cold air

17

13 Same burner supplied

15.5 with hot air

167

19.7 33

21.7 For an equal amount of light, the saving of gas=33 per cent. an equal consumption of gas, the gain in light=62 per cent.

4.2

2.2

| 2-6

27

3.0

The temperature necessary to render substances incandescent may be imparted to them in various ways. It may be given directly by mechanical power, as in the “steel mill,” formerly used in coal-mines. Usually, however, chemical action is employed, as in gas, candle, and oil-flames; or electricity is used, as in the various forms of electric light.

The conditions necessary for a good and satisfactory artificial light were now examined. In the first place, the light should contain all colours; that is, it should be capable of showing every variety of tint which will be exposed to it. This is the case with the carbon electric light, and that of candle, oil, and gas flames, since the light from these sources contains all the colours of the spectrum, But there are many colours which the mercurial electric light is incapable of showing, since they are absent from its spectrum. It was also shown that all pure colours, except yellow, were perfectly black, when seen by the light of incandescent sodium vapour.

Solar light, although in so many respects superior to artificial light, is defective as regards the showing of colours. There are certain colours which cannot be seen by solar light-for instance, all the colour which can be seen by the sodium flame is quite invisible in daylight. If a pigment could be made of such a yellow colour as to be of exactly the shade of that produced by the sodium flame, it would be absolutely black in solar light. But our pigments are all mixed colours, and no such pigment which thus entirely disappears in the light of the sun is known. But in addition to this tint of the sodium Aame, there are hundreds of other tints which are also not present in the solar spectrum, and which are consequently invisible in daylight.

Although solar light is inferior to artificial light in the completeness of its colours, yet, in another respect—in the comparatively small amount of heat which accompanies its rays in proportion to the light itself—it is greatly superior to every sort of artificial light. The great amount of heat in our artificial lights is absolutely useless. It is nearly all intercepted by the humours of the eye before it reaches the retina, and, no doubt, produces that irksomeness which is felt after working in artificial light for any considerable time, and which is not experienced from daylight.

The speaker concluded as follows:- The history of artificial illumination cannot fail to impress upon us the difficulties in the way the application of scientific discovery to the utilities of life. How long was it after the discovery of the production of gas from coal, before a manufacturer could be found to bring it into actual operation? Thirty years ago, working in his laboratory at Blansko, Reichenbach showed us the process by which we could obtain paraffin and paraffin-oil from bituminous coal ; but the discovery remained unheeded for twenty years. More than thirty years ago, Mr. Faraday pointed out a source of the electric light in the permanent magnet ; but we are only now beginning to use it for illuminating purposes. The brilliant little spark was long looked upon as a mere scientific curiosity, and is only

of

now beginning to flash across the sea, guiding the mariner safely into barbour, or warning him from approaching a dangerous coast. How long will thermo-electricity have to wait before it receives a similar application? In thermo-electricity we have a direct transformation of the force of heat, which we obtain with such great economy from coal, into an electric current, and this, by further education and development, might be rendered available in the production of the electric light. Hitherto, its application in this direction has been altogether unheeded, and yet, of all sources of the power necessary for the electric light, thermo-electricity evokes this power most directly from coal. In the magneto-electric light we have the great disadvantage, that the heat of burning coal must be first transformed into mechanical power, which is made to rotate the armatures of magnets, and thus produce the necessary electric current. In this transformation of heat into mechanical power there is no less than 9-10ths of the original force in the coal absolutely lost. Hence the advantage which would result from the direct application of heat to the production of the electric current.

The man of science rejoices in the discovery of truth for its own sake. He gives his results freely to the world. It is no part of his duty, it is not his function, to apply those truths to the utilities of life. Success in this direction demands quite different powers of mind. Those who possess these powers, ought also to acquire the necessary knowledge which would enable them, with more facility, to seize upon the discoveries of science, and apply them to the wants of every-day life. This scientific knowledge is the link which, up to the present time, has so sadly failed in the application of science to the manufacturing arts.

[E. F.]

WEEKLY EVENING MEETING.

Friday, February 20, 1863.

HENRY BENCE JONES, M.D. F.R.S. Honorary Secretary, in the Chair.

Rev. GEORGE WILLIAMS, B.D.
SENIOR FELLOW OF KING'S COLLEGE, CAMBRIDGE.

On recent Discoveries at Jerusalem.
The Temple Area and the Fortress Antonia.

The chief interest that attaches to the discoveries lately made at Jerusalem by Signor Pierotti, corroborated, as they doubtless will be, in all main points, by the still more recent investigations of the Count

de Vogüé and M. Waddington in the course of last year, is derived from the remarkable confirmation which they afford to the received views of the topography and archæology of the Holy City, in the case of those sites which are of greatest importanoe in connection with its sacred history. I gratefully accept all the facts brought to light by Signor Pierotti, while I differ considerably from his inferences and conclusions. Here I shall state my own views, without entering into controversy.

As it would be impossible to do justice to all these discoveries in the course of a single lecture, I propose to confine my remarks to the site of the Temple and its contiguous fortress, Antonia. The situation of the former appears to be fixed beyond all possibility of doubt by the recent discovery by Signor Pierotti of the complete water system connected with the Hebrew temple, still existing as entire as when it was in daily use during the period of the Jewish commonwealth. The perfect preservation of this complicated system of aqueducts, drains, and reservoirs, is owing to the fact that they are all excavated in the solid rock, and therefore have not been affected by the demolition of the structures above, except so far as they may have become partially blocked up by the accidental falling in of debris of the ruined buildings.

Had history been silent on the subject, yet we should have been forced to conclude, from the account of the various sacrifices connected with the Jewish ritual, especially from the description of the numerous victims offered by Solomon at the Feast of Dedication, that there was a very complete system of sewerage connected with the Temple, introducing a large quantity of water to dilute the blood, which would otherwise have had a tendency to coagulate, and carrying off the blood and offal from the sacred precinct.

This, history tells us, was actually the case. The fullest account which is preserved of these waterworks is contained in the description of the Holy City and of the Temple worship, in a tract of Aristeas, who visited Jerusalem during the reign of Ptolemy Philadelphus, and who describes a vast series of reservoirs beneath the area of the Temple, supplied by a copious spring of living water, and connected together by pipes and conduits extending over a space of five furlongs. There were many openings to these hidden depths from the area above, the secret of which was known only to the ministers of the Temple; and the supply of water was so managed as to flush the whole court, and carry off the blood of the numerous sacrifices. This description is fully confirmed by the Mishna and other Jewish authorities.

This language, which might formerly have appeared exaggerated, is now proved to be literally correct; for those cisterns have been actually explored, and the conduits and drains traversed in all directions by Signor Pierotti; so it is no more matter of conjecture, but of ascertained and positive fact.

It was the happy suggestion of Professor Willis, and a striking

example of that marvellous intuition for which he is so remarkable in investigations of this nature, that the hole in the Sacred Rock of the Moslems, under the well-known Dome of their Mosk, and the cave in that rock, now so familiar to all from the frequent descriptions of many travellers, but especially from the drawings of Mr. Catherwood, were the drain and cesspool of the Jewish altar; and that the round hole in the centre of the rocky pavement of that cave was the mouth of the channel by which the blood, poured out at the horns of the altar, flowed off, according to the Mishna, to the valley of the Kidron. That theory of Professor Willis really implied the condition that, if ever the hollow in the rock under that circular stone should be explored, there would be found an aqueduct for bringing in a supply of water on one side, and a drain for carrying off the blood and water on the other side. Now such is really proved to be the case ; and Signor Pierotti has actually entered that lower cave by one channel, and quitted it by the other.

The supply of water, which no longer flows in these channels owing to various obstructions, was derived from the celebrated Pools of Solomon on the road to Hebron, south of Bethlehem, and was brought to Jerusalem by an aqueduct which still exists. It crosses the Valley of the Tyropæon by the artificial embankment which joins Mount Sion to the Temple Mount--the Bridge of the Jewish historian. It was then received into a well, sunk in the rock immediately in front of the Porch of El-Aksa, from whence it was distributed according to the exigences of the Temple worship; for the supply could be regulated according to the requirements of the season. The channel for the supply of the Temple ran northward from this well, under the wide causeway which leads from the north door of El-Aksa to the south gate of the Dome of the Rock, passes under the stairs opposite the Gate of Prayer, and so through the rock of the raised platform into the lower cave, as already described, which marks the site of the altar of the daily burnt-sacrifice. When this is once ascertained, the whole Temple can be laid out, with the help of the tract Middoth (Measures) in the Mishna ; and it is a curious and interesting fact, that when the various parts of the Temple are distributed and adjusted according to these measures, the interval between the western wall of the Holy of Holies and the boundary-wall of the inner Temple, is exactly what it ought to be, supposing the western limit of the inner Temple to correspond with that of the raised platform of the Haram, which, as being cut in the live rock, has probably remained unaltered from Jewish times.

The drain from under the Jewish altar then runs northward for a distance of 120 feet, to a large double cistern, hollowed in the rock of the raised platform of the Haram. The Jewish authorities inform us, that the place where the victims were slaughtered, the hooks to which they were hung for the purpose of being flayed, and the marble tables on which they were dressed, and the parts appropriate for the sacrifice separated and prepared, was to the north of the great altar. Here, therefore, would be the greatest effusion of blood and other matter

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