though without his own knowledge or expectation; he was facilitating and prolonging the enjoyment of light, enlarging the avenues of science, and conferring the highest and most lasting pleasures; he was enabling the student to contemplate nature, and the beauty to behold herself.

Every page of the history of science records the unexpected extension of apparently insignificant discoveries, and it is more than probable that posterity will smile upon the knowledge of the present age, with the same complacency that we now contemplate the ignorance of former times; it was an irrational complaint of a late philosopher, that his existence had not been reserved for a future age, when knowledge should approximate perfection; facts will accumulate, and new sources of information rush upon us, but the boundaries of knowledge will always recede.

ART. IX. On the Cause of the Diminution of the Temperature of the Sea on approaching Land, or in passing over Banks in the Ocean.-By Sir H. DAVY.

IN the Third Number of the Journal of Science and the Arts an extract of a letter from my brother, Dr. Davy, has been published, containing some observations on the temperature of the ocean and the atmosphere in the equatorial parts of the globe. I have since communicated to the Royal Society a long letter which he has written on this subject, and which will be published in the next volume of the Transactions. A nongst other philosophical remarks, those by which he confirms the conclusion of Mr. Jonathan Williams* and other observers, that the temperature of the sea always falls in shoal water, and that the thermometer may be made an useful instrument in navigation, appear to be very important.

Mr. Williams attributes the effect upon the thermometer on the approach of land to the cooling power of the land; but

* Thermometrical Navigation, Phil. 1779.

this reason will not apply to the effect of shoals in the ocean, or to the tropical climates. M. de Humboldt, in his personal narrative, seems to consider it as resulting from cold currents below the surface; but in his work he does not enter into any minute details, nor in a conversation which I had with him on the subject, did he pursue it any further than in mentioning this general opinion. Dr. Davy has merely noticed the fact as a general law; but has not speculated upon the cause of it.

The great interest of the subject to the practical navigator has induced me to consider the theory of it rather minutely, and I shall now detail my views. The same reasons, I have no doubt, either have occurred, or will occur to M. de Humboldt and to Dr. Davy; but I am sure no apology will be necessary for anticipating those either to my brother, or to the illustrious Prussian traveller, whose candour and urbanity are equally distinguished with his knowledge and sagacity.

The solar rays produce very little heat in passing through the air; but during their transmission through a body so imperfectly transparent as water, there can be no doubt that the same cause which occasions a loss of light must communicate an effect of heat, and consequently the greatest heat must be produced at the surface of the sea, and it must gradually diminish as the rays penetrate deeper.

The heat of the surface of the ocean must, at a great distance from land, depend upon the absorption of the solar rays: the cooling of this surface upon its radiating powers, and upon evaporation. But water is an imperfect conductor of heat; and by cooling as far as 38 or 40 of Fahrenheit, its density is increased when cooling agencies act upon an unfathomable ocean, the strata of water cooled sink out of the reach of the surface, and very little influence the temperature of this surface; but when cooling agencies act upon a shallow part of the ocean, the cooled strata accumulate and approach nearer the surface, and cause the temperature of the ocean, at its surface even, to be nearer the mean temperature of day and night. In very shallow water close to the shore, the bottom will be heated; and during the day the temperature close to the

shore will be higher than that of the ocean; but in the night, as the land cools faster than the sea by radiation, the air having its temperature lowered by contact with the cooled land, will flow down upon the sea, and thus will destroy the effect of the hot water flowing from the extreme shallows, and at a certain moderate distance will produce such a diminution of temperature as will more than compensate for the heat produced by contact with hot land. Hot air and water, within limits above 52°. always rise; cool air and water above 40o. sink; therefore, by whatever cause cool air or water are kept near the surface of the ocean, that cause will diminish the general temperature of that surface.

It has been supposed by Mr. Perron, and other inquirers, that ice may exist at the bottom of the ocean; but simple physical reasons show that this is impossible, unless the temperature of the surface of the ocean is below 40°. for water at 40°. is heavier than at the freezing point. Ice, as Count Rumford has shown, always forms at the surface; and ice at the bottom of any part of the ocean, must begin to thaw when the temperature of the surface is above 40°. for hot currents then descend and cold ones rise.

The same causes must always operate, where the heat of the surface of the ocean is above 52°., and under these circumstances, whether in the equatorial, polar, or tropical climates, land or shallows must always lower the temperature of the ocean but in very high latitudes, if the heat of the surface should approach to 40°. only, the thermometer will no longer be a guide of land to the navigator, for water is heavier at 47o than at the freezing point 32o: but such an occurrence can only happen in icy seas.

ART. X. New Neapolitan Botanical Works.

APPENDIX prima ad catalogum plantarum Hortii Regii Neapo litani, anno 1813 editum ; cum appendice plantarum FLORE NAPOLITANE que nondum in Horto Regio coluntur; adjecta SYNOPSIDE Novarum Plantarum quæ in Prodromo Floræ

Napolitanæ anno 1811-13 editio describuntur. Autore Michaele Tenore, Eq. aur. et M. D. Neapoli, 1815. 8vo. pagg. 76.

WE have not seen the catalogue to which the above is an

appendix. The present part is a naked enumeration of the names of plants in the royal botanic garden at Naples. With the exception of some new species indigenous of that part of the world, we have met with nothing which is not well known in the collections of this country. But the concluding Synopsis of the new species contained in the FLORA NAPOLITANA, a work which we have not met with, as far as we can judge from a very slight inspection, seems important, and contains fully expressed diagnoses of one hundred and eighty-five unpublished, or rare species, with critical observations. If such have been substantiated after due attention to synonymy, so often and so reprehensibly neglected by the French and Italian Botanists, a very valuable acquisition to European botany has been made. We regret that the Italian publications find their way so slowly into this country.

FLORA NAPOLITANA; an account of the indigenous plants of

the Neapolitan territory, together with some exotic ones cultivated in the royal botanic garden at Naples; by Dr.

Tenore.

The first volume of this work was completed in 1815; it is in atlas folio, on vellum paper, and contains one hundred leaves of letter-press, with fifty engravings coloured from nature, and cost 100 ducats, or 440 livres, about 20 pounds, The work is to be completed in four volumes of nearly equal extent. The Linnean arrangement has been followed; the text, except in the specific diagnoses, is in Italian, a fasciculus of ten leaves and five plates is published every fourth month. About 3000 species, of which 200 are deemed either entirely new, or as having been imperfectly known, will form the con tents of the whole publication.

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ART. XI. Proceedings of the Royal Society of London. THURSDAY, March 6th.-A paper was communicated by the Rev. F. H. Wollaston, describing a thermometer, calculated for measuring heights. It is well known, that the boiling point of fluids is regulated by the pressure of the superincumbent atmosphere, and that the higher we ascend, or in other words, the lower the barometer is, the less is the temperature required to boil water. Accordingly the temperature at which water boils, is inversely as the barometrical pressure. Mr. Wollaston here describes a thermometer, the construction of which is so delicate, as to be capable of indicating the difference of temperature required to boil water upon a table, and upon the ground; consequently, the heights of rooms, houses, churches, and mountains, are easily ascertainable by it. The instrument is most ingeniously contrived, but cannot be well understood without the plate. The first effect of expansion drives the mercury from the great bulb into a smaller one just above it, and then, as the boiling point approaches, the quicksilver passes into a capillary tube of such fineness, that 1°. occupies about an inch in length of the tube; and the height of the mercury is read off by a properly applied vernier. We must refer our readers to the paper in the Transactions for the method of using this very delicate instrument, and also for the evidence of its correctness.

March 13. Mr. Pond gave in an appendix to his former paper on the parallax of the fixed stars.

March 20. A paper was communicated by the President, from Mr. Marshall, giving an account of the culture and produce of the laurus cinnamomum, or cinnamon laurel. The reading of this paper was continued on the 27th, and terminated on Thursday, the 17th of April. Its length prevents our giving an intelligible abstract of its various contents, in the limits we can afford.

At the same meeting, three mathematical papers were presented to the Society; two by Thomas Knight, Esq. and a