The night was rather squally and cloudy, with occasional

showers.

Feb. 10. 1820. S. Lat. 2° 8', East Long. 81° 54'.

The night was boisterous, with heavy rain, and some thunder

and lightning.

Feb. 11. 1820. S. Lat. 4° 45', East Long. 81° 54′.

The wind was fresh during the night, and the sky pretty clear, with occasional showers.

These Hygrometrical observations were made with two thermometers, one of which had its bulb covered with an absorbent substance, and wetted with wa ter. The degrees in the column show the descent of the mercury by the cold, produced by evaporation.

The night was rather squally, with some heavy showers. Between about N. Lat. 3° and S. Lat. 7° or 8°, a north-west or westerly wind prevails during the same month that the northeast wind prevails in Ceylon. About the limits of the NE. and NW., and of the SE. and NW., calms commonly occur. Hence, we may expect, that as those parts of the ocean within the Tropics are particularly liable to calms, the temperature of the water will be unusually high, and that in those parts of the ocean within the Tropics which are particularly liable to squalls, the temperature of the water will be lower. The north-west or little monsoon blows from Madagascar, and the direction is probably connected with that great island. The NW. is succeeded by the SW. monsoon, in the above latitudes.

Feb. 13. 1820. S. Lat. 7° 57', East Long. 82° 52′.

The night was calm, with frequent showers.

Feb. 14. 1820. S. Lat. 7° 59, East Long. 82° 20.

Till midnight there was a fresh breeze, which was followed by a calm and much rain.

S. Lat. 8° 34', East Long. 81° 29'.

Feb. 15. 1820.

The night was clear and calm, and there was some swell from

the SE.

Feb. 16. 1820. S. Lat. 9° 3', East Long. 81°.

Wind and Weather.

SE. very gentle, pretty clear.

The night was calm and fine.

Feb. 17. 1820. S. Lat. 9° 19, East Long. 80° 39′,

The night was rather fine, and the wind occasionally ap

proaching to fresh.

Feb. 18. 1820. S. Lat. 10° 8', East Long. 80° 29′.

Feb. 19. 1820. S. Lat. 10° 27', East Long. 80° 25'.

The night was stormy and rainy, and the wind blowing a gale. During this gale, the sky was thickly overcast, so as to be of a dark grey or light sootty hue, but the sea retained its usual colour. Its blue colour appeared very distinct, when one looked immediately down from the ship into the sea, and it was equally evident in the waves as they rose, their heads being between the light and the eye of the observer. Even in the colour of the surface of the sea in general, a tint of blue might be distinguished, but it was not bright, on account of the darkness of the surface. Hence, we may infer, that the ocean does not owe its blue colour to the reflected azure of the sky, as several authors have supposed.

ART. XX.-Observations on the Structure and Functions of the Canal of PETIT, and the Marsupium Nigrum, or peculiar Vascular Tissue traversing the vitreous humour in the Eyes of Birds, Fishes, and Reptiles. Communicated in a Letter to Dr BREWSTER, by ROBERT KNOX, M. D. F. R. S. E. &c. &c. MY DEAR SIR,

IT

IT may perhaps be in your recollection, that in the Essay which I had the honour to read before the Royal Society of Edinburgh, on the Comparative Anatomy of the Eye in June. 1823, and in the several memoirs connected with the same subject, which I have subsequently submitted to that learned body, I had not been able to determine, with any precision, the nature and functions of the pecten or marsupium nigrum, found invariably, I presume, in the eyes of birds. After I had ascertained (what indeed had been done previously), that it is very vascular, and generally dark coloured, that it contains a quantity of loose cellular tissue, and no nerves, and that it seldom procecds so far as the lens, passing only a certain way into the vitreous humour, I found, that all the questions of high physio logical interest, connected with this peculiar structure, still remained unanswered. For example, there did not appear any satisfactory or sufficient reason why this vascular tissue was placed in the centre of the vitreous humour; neither had any one shewn its true functions. To clear up these points, I repeated a number of my dissections, and arranged a series of preparations of the vascular tissues of the eye in birds and quadrupeds, illus trative of some of my opinions. These preparations, together with an Essay on the subject, I had the honour to submit to the Royal Society on the 15th of March. The following very brief Abstract will, I trust, enable the readers of the Philosophical Journal to comprehend the general views I have adopted relative to the subject *.

* The Memoir is not confined altogether to an inquiry into the functions of the Marsupium; several other points relative to the comparative anatomy of the Eye are briefly discussed.