are adopting the last Atlantic model, consisting of a few iron or steel wires embedded in hemp. In no former Exhibition has there been so good a collection of raw and manufactured produce; but the specimens were often so widely scattered that it became a task of no little difficulty to make fair comparisons. Great attention was given to mining and mining apparatus, especially by France, and her collection of Civil Engineering models was one of the most interesting parts of the whole Exhibition. Since 1862 France and Belgium have wonderfully improved in the manufacture of iron and steel, so that this country is not now so far ahead in its iron manufacture as was formerly the case. Foreigners now, also, make more of their own tools and machinery than heretofore; and although their best specimens are generally copies from English models, they can now, for all practical purposes, turn out in many places as good machinery as could be obtained in this country; in excellency of design, however, and in finish, there is still no country that has come up to the standard of English manufactures. Alarmists have raised the cry that England is not keeping pace with the advancements of other countries, but we are disposed rather to believe the truth to be that whilst we steadily advance, other countries, which a few years since were much behind us, have made themselves acquainted with all that we possess, and thus are able to make more rapid strides, and to lessen the distance between us and themselves. It has been, undoubtedly, principally through the instrumentality of International Exhibitions that other countries have made themselves acquainted with our arts, and we have learned theirs; and thus the diffusion of knowledge throughout the world has been hastened and extended. The rapid growth of these Institutions may at length be said to have reached a fair limit, and although the first International Exhibition resulted in a large pecuniary surplus, subsequent ones have not, in most cases, even succeeded in paying their expenses, and it stands to reason that the larger the Exhibition, the more expensive it must be, and consequently the less likely to prove remunerative. For the future, then, it may be anticipated that International Exhibitions will not be so general as heretofore, but will rather be confined to one class of objects, by which means it will be possible to hold them in some permanent building for which a rent only would be paid, and thus the chief expense which now attends their promotion will be obviated. III. ON THE LUMINOSITY OF THE SEA. BY CUTHBERT COLLINGWOOD, M.A., M.B., F.L.S. DURING my recent expeditions as Naturalist on board H.M.S. 'Serpent,' one of the subjects to which I was anxious to pay especial attention was the luminosity exhibited by the sea, its appearance and various forms, the various conditions under which it became manifest, and, as far as possible, the causes which produced it. These points have already engaged the attention of observers, but much remains yet to be learned, nor shall I profess to add a great deal to what is already known, but shall simply relate the result of my observations carried on at every opportunity during a year and a half. Not a night passed while I was at sea without my looking out for luminous appearances jotting down anything novel or unusual, and where practicable, making an examination for the detection of the cause of the luminous appearance ;--and although the moonlight nights were very beautiful, I often bewailed the invisibility of the luminous animals whose light was extinguished by the effulgence of the moon's rays, and longed for a return of the dark nights when the brilliancy of the stars compensated for the absence of the moon, without putting a stop to my observations on the luminosity of the sea. I would classify all the cases of luminosity which have come under my observation under the following five heads:1. Sparks or points of light. 2. A soft, liquid, phosphorescent effulgence. 4. Instantaneous recurrent flashes. 5. Milky sea. The first of these, or the appearance of points or sparks of light, is by far the most common, and in different degrees may be said to be all but universal. Whether the other forms of luminosity are exhibited or not, sparks of light in greater or less abundance are scarcely ever absent. The sea, more particularly when agitated, sparkles with brilliant points of light, varying in size from that of a pin's head to that of a pea-and of greater or lesser permanencysome being almost instantly extinguished, while others retain their light for an appreciable time. I do not think I ever looked at the sea on a dark night without seeing some few sparks, even though I might enter a remark that the sea was "not luminous to-night." But usually these sparks are abundant, and on occasions they present a wonderfully brilliant appearance. On one occasion, when this phenomenon was unusually striking, on the coast of China in lat. 26° N., on drawing up bottles full of water and pouring it out in the dark, the water sparkled brightly as luminous points ran over, but a close inspection revealed nothing in the water but a few minute entomostraca. On another occasion when some water which had been left in a basin exhibited luminosity at night, I got a very brilliant spark upon my finger, and taking it to the light, it proved to be a minute crustacean. The second form of luminosity to be noticed occurs comparatively rarely. It consists of a soft, usually greenish light, which only makes its appearance when smooth water is disturbed, and is only seen in calm weather. This form appears identical with what we see nearer home, as on the shores of Ostend and in the estuary of the Mersey. This form of luminosity I have observed on only three occasions, and under similar circumstances, and I have reason to believe that the cause is the same on all occasions, whether in the Eastern seas or in the Mersey. On the 5th of July being on the coast of China, in lat. 27°, the weather in the afternoon became dead calm, and after sunset I remarked that the sea was beautifully luminous, but altogether without conspicuous sparks or points of light. Wherever the ripples caused by the advancing ship rolled away, they were crested with bright green light, and the ship's hull appeared to be enveloped in a luminous sheath. On this occasion the effect did not last long, and I did not examine the water microscopically. The next time I noticed this form of luminosity was in Singapore harbour, on November 6th. The wind was east, thermometer 76°, weather fine. The water was like glass, smooth and beautiful, but exhibited no light except when disturbed; but every oar-stroke of the boat in which I rowed produced eddying circles of light, and a lovely soft green glow crowned every ripple from the bows. A splash in the water produced a shower of a myriad minute sparks, the aggregate of which made up this delicate luminosity, which I never saw so beautifully exhibited as upon this night. The following night the same effect was visible, but scarcely so intense as before (wind N.E., temp. 76°), and on the third night (the wind being E. and temp. 75°), I again observed it. After this I was absent from Singapore two nights, and on my return I no longer noticed the luminous effect. On each of these three nights, I examined the water;- as I filled a bottle, bright sparks of light adhered to my hands, and on bringing it to the light I found that it contained a number of small globular greenish bodies, which floated upon the surface for the most part, but appeared to have the power of freely moving in the water. On closer examination these bodies proved to be Noctilucæ; and during the night I observed that the contents of the bottle frequently flashed with bright and rapid coruscations. I had no difficulty therefore in coming to the conclusion that the peculiar luminosity in the harbour was due to the presence of innumerable Noctilucæ. On the 24th of May, lying in Simon's Bay, Cape of Good Hope, the water was similarly luminous. The weather was fine, wind W.N.W. light, bar. 30 04, thermom. 60°. On examining the water closely I found that, as before, the luminous effect, though soft, subdued, and apparently uniform, was really due to innumerable small sparks, and on bringing the water to the light, I found numerous Noctilucæ in it, precisely similar to those observed at Singapore. They were not, however, in sufficient numbers to have produced all the light, for in a wine-glassful of water there were on an average not more than a dozen Noctilucæ. But besides these bodies, there were a great number of motes in the water, many of which on closer examination appeared, by their rapid jerking locomotion, to be minute Entomostracous Crustacea. They were so minute, that by the imperfect light on board ship I long tried, in vain, to secure one to place under the microscope. Besides these were some larger species of Entomostraca. The Noctilucæ measured from to ss of an inch in diameter; they were of a pale greenish colour when seen with the naked eye, closely resembling Volvox in appearance, but with a much less active movement. They had, however, powers of locomotion, though the means were not apparent under the microscope. They had a dark nucleus, usually irregular, but in some cases spherical and well defined. Their circumferential outline was very faint, and their general aspect very variable. A kind of slit appeared to extend through two-thirds of the body, from which faint lines radiated, usually having a double outline, and not reaching the circumference of the sphere, but often terminating in large round granular bodies of various sizes. The whole body was studded with oil globules of various sizes, which strongly refracted the light; but slight movements, which appeared to be taking place in an almost imperceptible manner, soon changed the whole aspect of any individual Noctiluca while under observation, so that the description or drawing of one minute did not answer for the next. Each Noctiluca had a large curved cilium projecting beyond the body, and apparently taking its rise from the nucleus. This form of luminosity, although very striking, appears to be completely extinguished by moonlight, even when the moon is young. It appeared, only less marked, on the two following evenings, and on the third we left the bay. I am informed that Simon's Bay has been remarked as frequently exhibiting this phenomenon. On the 7th of July, in lat. 28° N., on the coast of China, two days after the occurrence of this form of luminosity, as before noticed, a heavy swell coming in from the S.W. was met by a N.E. wind, and the ship rolled tremendously. The sea was beautifully luminous, every wave breaking into a pale light which was visible at a considerable distance, so that the whole sea was streaked with light, and again that peculiar phenomenon of the ship sailing in a luminous sheath was visible. The night was very dark, and it was lightning vividly and incessantly; the whole scene was eery and weird in the extreme. I mention this case because it was one of the most striking instances of general luminosity which has come under my notice; it appeared to be compounded of the two forms I have already described. The third form of luminosity to be described consists of moonshaped patches of steady white light, which I have found to be a very common phenomenon under certain circumstances. Next to the occurrence of sparks and always accompanied by them, this form of luminosity is most frequently seen, and does not appear to be confined to any particular locality. I first observed it in the Mediterranean, on the first night on which the absence of the moon allowed it to be visible, and I have since found it to be no less frequent in the Red Sea, the Indian Ocean, the China Sea, and the Atlantic, north and south of the equator. It is most commonly visible in the wake of the ship, and consists of numerous round patches of light, which might be mistaken for white-hot shot of various sizes beneath the water at different depths. Sometimes, when deep down, they were pale and of a whitish colour, with indistinct outline, and of large size, but when nearer the surface they were smaller and more distinct, and assumed a pale greenish tinge. They usually remained visible for 8 or 10 seconds, but sometimes less. As these appearances were just such as might be presented by the umbrellas of large Medusa, were such present and luminous, I was strongly inclined at first to attribute them to this cause; and the fact that on one occasion (about a week after I left England) I saw these moonlight patches in the Red Sea on the evening of a day on which the ship had passed through a shoal of Aurelia, led me to attribute them to this cause. I supposed that the Aurelia, struck by the screw, gave out their light under the excitation of the blow, and floated away luminous and dying. But I was forced to abandon this theory afterwards, for I have since many times watched for floating Medusa before the light failed, and not seen VOL. IV. 2 L |