Phladda Island near Easdale, Runa Gall in the Sound of Mull, Corran Point in Loch Linnhe, and another is now being fitted up at MacArthur's Head, in the Sound of Islay. It has been computed, that the saving in first cost and consumption of oil, consequent on adopting this improvement at these six lighthouses, amounts, on the most moderate estimate, to about L.385 annually.

Since the first application of this principle of allocating the light to the different azimuthal arcs in the compound ratio due to their lengths of range, and the number of their degrees in azimuth, various improvements and extensions of the same principle have occurred to me; and I now, as a supplement to my first communication, add the following cases, both for revolving lights, and for fixed lights which require to show all round the horizon :

Revolving Lights of Unequal Range which do not Illuminate the whole Horizon.

Revolving apparatus, where the whole horizon does not need to be illuminated, may, like the fixed apparatus, be similarly condensed. The power may be increased in the required directions in different ways, according to the size of the apparatus and the local requirements of the coast line. As, for example, at the Skervuile Rock, in the Sound of Jura, (where I first thought of applying the condensing principle to revolving lights), the method that seemed most suitable was to have the vertically straight prisms or mirrors for diverting the light into the required arc (vide vol. i. p. 273) fixed outside of the revolving apparatus. By this arrangement, whenever the revolving lenses passed out of the illuminated arc into the dark arc, the beams of rays emanating from them would be reflected by the series of prisms or mirrors, so as to pass over the arc that needed strengthening, which would thus be illuminated at the same instant by a direct and a reflected beam. The erection of a light on Skervuile was, however, delayed, and still remains in abeyance, and nothing was done regarding this plan of condensing. At MacArthur's Head, which was at one time (1859) intended to revolve, the apparatus was so large that the lantern would not admit of reflec

tors being fixed outside of the apparatus, as proposed for Skervuile, and the mirrors were therefore to have revolved along with the lenses, &c.* Attached to each mirror was a rod or standard, projecting downwards, with a roller on its lower end, which in its transit over the dark arc passed up an inclined plane fixed to the trimming-path. In passing over the inclined plane the rollers would of course rise upwards, and raise the mirrors to the level of the lenses, so as to intercept the beam of light, and reflect it parallel to a beam from one of the other faces of the revolving apparatus, and thus direct it to the azimuth where additional strength was wanted. At the other extremity of the dark arc, the rollers were to be lowered by descending another inclined plane, and the mirrors descending with the rollers below the level of the lens, became again inoperative. After the drawings had been nearly completed, the character of the light was altered from a revolving to a fixed light, so that the plan has never yet been carried into practice. Other mechanical arrangements may, however, be found preferable in some cases.

Fixed Lights of Unequal Range, which Illuminate the whole

Horizon.

At fixed light stations, which require to show all round the horizon, but which are placed, for example, on an island very near the shore-it becomes desirable to allocate the power in proportion to the lengths of range in the different azimuths. The light should for those azimuths (which require to be more or less powerful than the rest) be collected into beams of parallel rays by sectors of holophotes proportionate in horizontal angle to the power required. There should then be placed in front concave divergers, straight vertically, and of such horizontal curvature as to spread the incident parallel rays over the required arcs. The light will thus be made to show all round the horizon, of power equal to a fixed light of the ordinary kind, in those azimuths where the ordinary fixed light apparatus is placed, and of different powers in the azi

*My friend, Mr James Balfour, C.E., has lately suggested to me, that where the apparatus is of small size, one continuous mirror might be employed instead of a series of separate mirrors. This mirror should of course be a logarithmic spiral.

muths in which the holophotes and divergers are placed. For by this arrangement, the light will be reduced in the azimuthal plane below the standard of the light from the ordinary fixed apparatus, or increased above that standard in proportion to the allocation and separation of the rays effected by the compound action of the holophotes and the divergers. One of these agents could generally be saved in the refracting part of the apparatus, by making it disperse or condense horizontally, while still continuing to parallelize vertically, though it might perhaps be impracticable to make such a change in the totally reflecting prisms, the execution of which is already difficult enough. This, however, is of no consequence, as it would in all cases be sufficient to restrict the condensation and expansion, to those rays which pass through the refracting part of the apparatus only; for even the shortest range would probably need all the light which comes from the prisms.

Revolving Lights of Unequal Range, which Illuminate the whole

Horizon.

When a revolving light is placed, for example, on an island situated in a long and narrow sound, and is required to show all round the horizon, it is obvious that, as in the case of the fixed light in similar circumstances, it should not be equally powerful in every direction. The simple method of distributing the rays properly, in many cases, is to place between the lamp and the revolving apparatus zones of spherical mirrors (whose centre of curvature is in the flame), or by placing outside of the apparatus portions of straight prisms, or mirrors of such horizontal curvatures as may be necessary for the different localities, or by a combination of these agents. The vertical breadths of these internal or external agents will depend on the lengths of range in the various azimuths, so as to divert that portion only of the light which can properly be spared from one azimuth to assist another, while they allow the remainder of the rays to continue in their original direction. The varying breadths of these agents which intercept a part of the light in its ordinary course, but which still permit a limited portion to pass above and below them, will therefore represent inversely the varying distances of the NEW SERIES.-VOL. XIII. NO. II.-APRIL 1861.

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neighbouring shores from the lighthouse. This ratio, which is probably inversely as the squares of the distances from the shore, would require to be ascertained by a series of experiments.

The allocation might also in some cases be effected by a modification of the method already described for fixed lights, which show all round the horizon. To attain this there would be placed between the lamp and the revolving lenses agents which expand or condense the rays as required over the different arcs. But as the rays so altered in direction would not fall properly upon the lenses, an additional agent* would need to be placed close to the lenses, in order to give the expanded and condensed rays the same amount of divergence as if they had proceeded straight from the centre of the flame, which is the focus for which the lenses are calculated. For this purpose, supposing that we are dealing with an arc that has to be weakened, from its being opposite to a part of the coast-line which is near the lighthouse, the agent placed next the flame would cause the incident rays to proceed as from a virtual focus short of the lamp, or, in other words, would increase their divergence. The action of this instrument would therefore be to expand the rays incident upon it, and which came from but a small horizontal portion of the flame, and to spread them over the whole of the larger arc, where a small amount of power is sufficient. The second agent, or that next the revolving lenses, would intercept these expanded rays before they fell upon the revolving lenses, and would reduce their divergence, so as to make them proceed as from a virtual focus situated in the centre of the flame, so that they would then be incident on the revolving apparatus in the proper directions. In other words, the second agent would undo the action of the first, but not until the rays had been spread equally over the expanded arc, and had extended so far outwards as nearly to reach the lenses. In the case of an arc of condensation, the arrangement would be nearly the converse of the former. In both cases the agents would only require to act in the horizontal plane, the centre of their vertical curvatures being in the centre of the flame.

In some instances spiral mirrors might be arranged close

* In some few cases a single agent might be sufficient.

to the flame so as to send the light in the required direction, without so materially altering the direction in which it falls on the lens as to render a second agent necessary.

Notice of Skulls found at Kertch, in the Crimea. By DANIEL WILSON, LL.D., Professor of History and English Literature, University College, Toronto.

The stirring events connected with the Russian war, though already superseded in the popular mind by the memorable incidents of more recent warfare, have left behind them at least one beneficial result, in the knowledge we now possess of the geography and history of the Crimea; along with many valuable traces of the diverse occupants of that remarkable peninsula from the earliest glimpses of Greek colonisation along the shores of the Euxine Sea. From the date of the landing of the AngloFrench army in the Crimea in 1854, its geography, its ethnology, and its antiquities, all acquired a new interest; and the half-obliterated remains of its unheeded and long-extinct past were suddenly invested with a significance which stimulated further investigation, and led to literary and archæological disclosures of permanent value. Among its ancient historical sites, which, owing to peculiar circumstances, received a large share of attention, that of Kertch is, on various accounts, the most remarkable. Built on the site where, some 500 years before Christ, the Greek city of Panticapæum was founded, it was the centre of an area rich with memorials of the strangely chequered past, which has seen the same spot successively occupied by Milesian Greeks, Romans, Goths, Huns, Tartars, Genoese, Turks, and Russians. The Russian occupation of the Crimea dates only from a late period in the eighteenth century; but since then, a museum had been formed in the town of Kertch, in which were preserved many historical antiquities of the Crimean Bosphorus; and especially sepulchral relics recovered from the tumuli which abound on the site of the ancient Milesian colony.

Learning from an old fellow-student that he was about to proceed to the Crimea, to join the Army Medical Staff, I wrote