one for days and weeks together, and yet the moon-shaped patches have been as bright and as abundant as before; and again, when we have passed through a thick shoal of Medusa towards evening, the luminous appearances have not been more marked than usual, but even less so. Moreover, having secured one of these Acalephs, it has not exhibited any luminosity during the night.

Although, however, I ceased to regard the Acalephæ as the source of the luminous appearances in question, there can be no doubt that the great numbers which are always visible immediately under the stern are due to the fact of the eddies of the ship exciting the emission of light in certain animals capable of exhibiting luminosity. Not however that similar appearances are never seen in other situations where they are unmolested, though I must say that in my experience this is rare. Thus in the Indian ocean, in lat. 121 N. and long. 55° E. (bar. 30°, them. 82°), among other appearances I noticed now and then a large patch of light with a roundish irregular outline pass by, emitting a pale and steady light, although out of the path of the ship; and on August 17th, being in a small boat on the coast of Borneo in a strong breeze after dark, I observed deep beneath the surface and entirely apart from any influence of the oars, the appearance of large globes of white light, shining persistently and spontaneously.

Although I long and constantly watched for the bodies which produced this remarkable and frequent luminous effect, I did so for a long time in vain. In vain I attempted to penetrate below the surface in search of any animals which could possibly originate the light. Although I could distinctly see the bottom of the ship's rudder, 19 feet deep, I could never detect a trace of any living thing within that depth by day, but no sooner did darkness supervene than they were often in abundance. It was only by accident, on June the 2nd, in lat. 28° S., and long. 9° E., that I was witness of a circumstance which seemed to elucidate the question. Looking as usual over the stern, there were plenty of moon-shaped patches, accompanied by sparks unusually large and bright. The patches were remarkably persistent, and could be traced for nearly half a minute after the ship had passed. They were evidently a considerable but varying distance below the surface of the water; when far down they appeared large and faint and ill defined, but when nearer the surface they were smaller, brighter, and better defined. As I watched, one of the bright bodies whirled about by the eddy of the rudder came absolutely to the surface and exhibited a nearly rectangular form of great brilliancy, of a pale green colour, and as far as I could judge about six inches long by two broad. It at once occurred to me that it was a Pyrosoma, and that this Ascidian was the usual cause of the phenomenon, the circular form of the patches being produced by the diffusion of the

light through a depth of water. I continued watching for a long time in hopes of seeing another, but although so good an opportunity did not occur again, many seemed to come near the surface, diminishing in size, but increasing in brilliancy as they did so; one particularly low down, suddenly gave out a dazzling brilliancy, producing a momentary effulgence all around.

I may mention that on a moonlight night when the moon has been dimmed by fleecy clouds, I have been able to see the moonlight patches, but when the moon shone out clearly they were no longer visible.

I have now to describe the fourth form of luminosity exhibited by marine animals, viz. momentary recurrent flashes of light. This form is nearly as commonly seen as the moon-shaped patches already described, which it very frequently, although perhaps not always, accompanies. If, however, the latter are well marked, the flashes are almost sure to be visible. I first observed them in the Indian ocean, north of the line, and since then, in the China seas and Atlantic. This appearance is very striking, but can only be seen under favourable circumstances, i. e. when the night is dark and the sea smooth. An indistinct transitory patch of light appears in the water, as evanescent as a flash of lightning; so rapidly does it come and go that it is difficult to fix the exact spot where it occurred. The brightness of the flash varies probably according to the depth of the animal producing it below the surface; sometimes it is of considerable brilliancy, and sometimes so pale that it would not have been noticed but for its suddenness. The colour is always whitish, and the form of the flash round, brightest in the middle, and becoming indistinct at the circumference. I have on some occasions seen these flashes occur in such numbers and with such rapidity that it would be impossible to count them, though more commonly they are comparatively few and far between.

But the fact which interested me most in these flashes of light was that they always occurred at a distance from the path of the ship. Although I have seen them accompanying the moon-shaped patches of light in the ship's wake, the places from which I could best observe the flashes were the forecastle or the gangways, when they could be seen in the smooth water several yards distant from the ship's side, and entirely uninterfered with by the ship's motion. This fact proved to me that there were spontaneous emissions of light by some animals below the surface, which voluntarily and at intervals gave out a bright coruscation. Moreover, although rarely, on following with the eye the spot where the flash appeared, it could be seen to reappear further astern, as though the emission was recurrent at definite intervals, as is the case with the luminous beetles called fire-flies at Singapore. I have also noticed on more than one occasion that the flash, instead of instantly disappearing,

was followed by a faint glow which vanished gradually, but whether this was an optical illusion of the retina or not, I cannot be sure.

Whatever may be the animals which produce these luminous appearances, they must habitually swim at a considerable depth. I never was able to make out any definite outline of the light, which always appeared more or less spherical with faint edges, and sometimes the size and faintness of the flashes seemed to prove that the light must have been diffused by its passage through a great depth of water, which would also account for the whitish appearance of what is probably really greenish light. But I am strongly disposed to believe that the sources of the flashes and of the moon-shaped patches are identical; in the one case emitting their light spontaneously, and in the other, under the excitation of the eddies produced by the ship, and especially by the screw-propeller when at work.

Before quitting the subject of these flashes, I must not omit to mention that while at Singapore, having taken some small Medusæ in a towing-net in the Straits, I placed them in a glass which stood by my bedside. In the night I observed them flashing brightly with instantaneous flashes, of the same character as those above referred to, although not the slightest shaking was applied to the bottle, or irritation to the animals. So also the Noctilucæ of Singapore harbour, which I kept similarly in a bottle, flashed fre quently with rapid and bright coruscations; and I am strongly disposed to believe that luminous marine animals in health, and acting spontaneously, without external irritation, always exhibit their luminosity in this manner, and that it is only when strong excitation is applied that they give out a steady but temporary glow.

There remains but one form of luminosity to be noticed, which although I have never been so fortunate as to witness it myself, has been observed by others, who have been longer at sea than I. This is what has been called milky sea, an extraordinary phenomenon of rare occurrence. It has been described to me as a general luminous glow, not confined to the crests of ripples or to disturbed water, but occurring in perfectly calm weather, and looking as though the whole sea was composed of a whitish fluid like milk, with no bright spots or sparks. Such an appearance reflecting a faint light upwards illuminates the ship, rendering every part of the rigging plainly visible, and inasmuch as it can only be seen in the absence of the moon, the contrast of the white glowing sea with the black sky produces an effect calculated to strike the observer with a kind of awe. Although I have met with persons who tell me they have not unfrequently seen this phenomenon, I am disposed to believe that it is extremely rare. One who has not really seen it at all might erroneously suppose, that such an appearance as I

have already alluded to as having twice occurred to me on the coast of China (when the ship seemed to be sailing in a luminous sheath) corresponded to the description of a milky sea, and in a small way it did so, and I considered it, at the time, as the nearest approach to it I had ever observed. But the milky sea must be something sui generis, and I imagine it to be owing rather to a condition of the water under certain peculiar atmospheric or climatic influences than to any extraordinary number of luminous animals in the water. A circumstance which occurred to me seemed to throw some light upon the subject and confirmed me in this opinion. Having put down the towing-net in the Formosa Channel it collected a number of small entomostraca, megalopas, minute medusæ, small porpitæ, pteropods, annelids, globigerinæ, &c., which I placed in a basin of sea water, and not having finished my examination of them they remained upon the table during the night. On stirring the water in the dark the whole became faintly luminous, giving out a general glow as if every particle were phosphorescent, the minute crustacea, &c., appearing as bright spots in the luminous fluid. If the slimy substance, in which in some marine animals at least the luminous property appears to reside, become diffused through the water, as it is probable it may be under certain combinations of conditions and circumstances, a general luminosity of the water may result, similar to that observed in milky sea, while its small sparks, doubtless in great abundance, would remain unnoticed in the universal glow, but would at the same time greatly enhance the general luminous effect.

There is a common idea that a southerly wind is peculiarly productive of luminosity in the sea, but according to my observations this is an error. The winds most prevalent when luminosity has been well marked have been westerly, north-westerly, or even easterly, south being perhaps the least frequent; but probably the direction of the wind has no special influence in the matter. What the favourable conditions really are it is as difficult to say as it is in the case of floating animals generally. I have seen remarkable exhibitions on one night followed by nearly absolute darkness on the next, the conditions of wind, weather, barometer and thermometer, being inappreciably altered. Probably temperature is as important as any influence; the luminosity in the Mersey only occurs in summer, and in rounding the Cape of Good Hope during the winter season, scarcely any luminosity was exhibited during the mouth that we were passing through the higher degrees of S. latitute.

The animals which I have observed to possess luminous properties are not numerous. Many of the more minute animals taken in the towing-net appear to exhibit them, more particularly the small Crustacea (Entomostraca) and small Medusa (Medusida).

I have no reason to believe that the large Medusa (Lucernarida) as Aurelia, Pelagia, Rhizostoma, &c., exhibit any luminous powers, having kept specimens which have invariably failed to do so. Nor do I believe that the Physophorida are luminous. I have never seen a luminous Porpita or Velella; and although on one occasion, when magnificent specimens of Portuguese men-of-war had been floating by all day, my attention was directed to shining spots at night, under the supposition that they were luminous Physaliæ, I merely replied by pointing to a bucket containing one of these animals, but which was perfectly dark. I have seen a large prawn give out light after death, and a fresh squid was illuminated at night with an irregular glow of whitish light, which remained unaltered as I passed my finger over the surface. Nor do I believe the stories of luminous fish, inasmuch as fish rapidly swimming in a fluid abounding in minute luminous points, as the sea sometimes does, would present an effect which an uninformed or inaccurate observer would readily mistake as proceeding from the fish itself, instead of from luminous points which it disturbed in its passage.

IV. OUR FIELD CLUBS: THEIR AIMS, OBJECTS, AND WORK.

1. Transactions of the Woolhope Naturalists' Field Club (established 1851), including the first part of the Flora of Herefordshire. By the Rev. W. H. Purchas, L.Th., 1866. 2. The President's Address and Reports for 1866, together with the Rules, List of Members, and Catalogue of Books of the West Kent Natural History, Microscopical, and Photographic Society.

3. The Proceedings of the Cotteswold Naturalists' Field Club for 1865.

4. Proceedings of the Bath Natural History and Antiquarian Club.

5. Report of the Liverpool Naturalists' Field Club for the year 1866.

6. Proceedings of the Bristol Naturalists' Society. Edited by Wm. Lant Carpenter, B.A., B.Sc.

NATURALISTS' Field Clubs, compared with other societies devoted to scientific pursuits, are institutions belonging to a very recent period: the oldest of them, in this country, has not yet celebrated its jubilee, and few have existed so long as ten years; yet now no season passes without adding to the already numerous list.