April 7.-The commencement of a paper, on the poison of fishes, by Dr. D. J. H. Dickson, was read.

April 21.-The communication from Dr. Dickson, on the poison of fishes, was concluded.

By the poison of fishes, Dr. D. does not mean the serious, and sometimes fatal consequences arising from wounds inflicted by the spines of the sting ray and other species of fish; but those which result from eating certain fish, or parts of fish. The journals of many voyages present us with instances of sickness more or less violent, accompanied by intumescence of the body, and irritating eruptions of the skin, being the consequence of eating certain fish. Often the noxious quality appears to reside in a particular part, especially the liver and intestines, as appears from the circumstance of those persons alone, out of a ship's crew, being thus affected who have eaten these particular parts. It is a matter of common observation that all fish are more wholesome and a more agreeable food before than after spawning; the fish, in the former case, being in high health and vigour, but in the latter, being sick, emaciated, and their muscular fibre becoming remarkably flabby. The difference between these two states, which in the temperate European climates seldom amounts to more than a difference in the agreeableness of the fish, considered as an article of food, often, in tropical climates, causes the same species to be in the one case a wholesome, and in the other case a very pernicious food. Again, certain species, especially in the West Indies, are observed at the same season to be wholesome in certain situations, and very much the contrary in others. Thus all the fish on the coast of Barbadoes are said to be safe food, even those which on the coasts of the other islands are deleterious. Examples also have occurred of a ship on one day falling in with a shoal of fish which proved perfectly wholesome, and on the very next day falling in with a second shoal of the same species which were found to be poisonous.

The cause of these differences it is not very easy to ascertain. The common test among seamen of the safety or hazard in feeding on any suspected or unknown kind of fish, is to put a piece of silver into the boiler together with the fish, and if the silver acquires a coppery colour the fish is considered as unwholesome. The coppery, or rather brassy colour thus produced, has probably been the reason why the flavour of fish in this state has been attributed to copper, with which they have been supposed to be infected by feeding on banks of copper ore. But the discoloration of the silver is probably owing to sulphuretted hydrogen, and it is a well-known fact that the drainings of a copper mine are so peculiarly noxious to fish that many lakes, formerly abundantly stocked, have been entirely depopulated by this very circumstance. Vegetable poisons swallowed by the indiscriminate voracity of this class of animals, have been con

sidered as the cause of the occasional unwholesomeness of their flesh; and Dr. Dickson is, upon the whole, inclined to adopt this opinion.

ARTICLE XVIII.

SCIENTIFIC INTELLIGENCE, AND NOTICES OF SUBJECTS CONNECTED WITH SCIENCE.

I. Meteorological Register kept at New Malton, in Yorkshire. January-Mean pressure of barometer, 29-463; max. 30-25; min. 28-65; range, 1.60; spaces described, 12.50 inches; number of changes, 24. Mean temperature, 34-200°; max. 53°; min. 25°; range, 28°. Amount of rain and snow, 4.36 inches. Wet days, 14; snowy, 5. Prevailing winds, W. and S.W.; E. 2; S.E. 1; S.5; S.W. 12; W. 10; Var. 1. Brisk winds, 8; boisterous, 8. Character of the period: wet, stormy, and changeable, with frequent heavy falls of snow and high winds, particularly by night, and the barometrical column in continual fluctuation.

February-Mean pressure of barometer, 29.453; max. 30-18; min. 28-67; range, 151; spaces described, 7.90 inches; number of changes, 17. Mean temperature, 34.41; max. 50°; min. 23°; range, 27°. Amount of rain and snow, 2.27 inches. Wet days, 7; snowy, 4. Prevailing winds, S. and S.W.; S.E. 2; S. 7; S.W. 15; W. 4. Brisk winds, 4; boisterous, 5. Character of the period: the first fourteen days cold, fair, and calm, with frequent hoar frosts; afterwards wet, stormy, and changeable, with strong gales, and much rain and snow by night.

March.-Mean pressure of barometer, 29-265; max. 30-36; min. 27-85! range, 2.51; spaces described, 12.50 inches; number of changes, 24. Mean temperature, 39-00; max. 57° min. 29°; range, 28°. Amount of rain and snow, 5.00 inches. Wet days, 13; snowy, 10; Haily, 1. Prevailing winds, W. and S.W.; N. 4; N.E. I'; S.E. 3; S. 3; S.W. 13; W. 6; N W. 1. Brisk winds, 9; boisterous, 5. Character of the period: tempestuous, with great falls of rain and snow. The tremendous storm of wind, with rain and snow, during the night of the 4th, caused a depression in the barometrical column in the course of nine hours nearly an inch and a half, the minimum being noted at one a. m. on the 5th; nor (with a single exception) did the barometer ever indicate 29.00 until the 13th, when the wind having veered from the S.E. by W. to N. there was a rapid increase of ths in a few hours. Abundance of snow fell during the time the column was thus depressed, frequently mixed with rain and hail. At one a. m. on the 25th, there was a loud clap of thunder, which was succeeded by the heaviest fall of snow

we have had during the winter; but the weather afterwards became more settled, and the barometer attained its maximum of elevation. It will be seen that the spaces described and the number of changes exactly correspond with those for January; but the mean is less than for many years past.

April.-Mean pressure of barometer, 29-581; max. 30-49; min. 28-89; range, 1.60; spaces described, 7.08 inches; number of changes, 14. Mean temperature, 42-96°; max. 60°; min. 29°; Wet Amount of rain and snow, 3.98 inches. range, 31. days, 6; snowy, 4; total quantity of rain, &c. this year, 15.56 inches. Prevailing winds, N. E. and N.E.; N.5; N.E. 9; E. 6; S.E. 1; S. 4; S.W.4; Var. 1. Brisk winds, 5. Character of the period: cold, wet, and changeable, and unfavourable to vegetation. On the 10th and 24th the violence of the snow storms was nearly unparallelled; and on the moors and wolds it lay in drifts several yards thick, and did considerable damage. From 10 p.m. (26th) to two p. m. (27th), we had a heavy fall of rain, attended with incessant, vivid red lightning and loud thunder all the time. The next day another thunder storm passed here to the S. and S.W. where it was visible from six to eight p. m.

When the above periods are compared with those for the last year, either as to the pressure, temperature, or to any other feature, there is no similarity whatever. The first four months last year were fair, dense, and mild; but those now elapsed have presented characters decidedly the reverse. The amount of rain and snow from January 1 to May 1, in 1817, did not exceed 3+ inches; and there were only 34 wet days; but the quantity of rain this year amounts to 15 inches, and there has been rain or snow in a greater or less degree on 76 days out of the 120.

New Malton, May 4, 1818,

J. S.

II. Analysis of a Specimen of the Diamond Rock. Dr. E. D. Clarke, Professor of Mineralogy at Cambridge, has examined a specimen of the diamond rock, from the banks of the river ligitonhonha, in Brazil, which was sent to him for this purpose by Mr. Mawe, of the Strand. It contains diamonds in their matrices. The rock consists of an aggregate of small quartz pebbles firmly set in indurated iron sand. The cavities in which the diamonds are placed are invested by a yellow ochreous matter which is full of minute pallets of native gold, visible to the naked eye.

From the same Professor we have also received an answer to the queries of our Lewes correspondent. The metallic lustre with which pure silica becomes invested when fused before the gas blow-pipe, is sometimes due to the charcoal used as a support; the same appearance takes place, under similar circumstances, in the fusion of corundum, and other refractory bodies, such as magnesia, and lime. But Dr. Clarke has observed

globules of a metal resembling silver when silica has been fused with borax before the gas blow-pipe, the difficulty of obtaining which is owing to their volatilization almost in the instant of their being formed. A still more remarkable result was obtained in the fusion of apatite; when a globule of metal was obtained, which is now in the possession of Mr. Lunn, of St. John's College, Cambridge. It is not pretended to account for these phenomena, but merely to state the facts, in the hope that others may confirm and explain then.

III. Comet of 1811.

During the course of the last year, M. Schröter, of Lilienthal, has published an account of the comet which appeared in 1811; and by comparing his observations on this comet with those which he made upon that which appeared in 1807, he has been led to form some singular conclusions. The nucleus of the comet of 1811, the apparent diameter of which was 1'49", and which, calculating from the distance, must have had a real diameter of 10,900-miles, M. Schröter supposes to be composed of a fluid covering a solid mass. In the centre of this nucleus we distinguish a second, which is smaller and more luminous, the apparent diameter of which being 16·97′′, gives a real diameter of 1,697 geographical miles. This central part was surrounded with a particular kind of atmosphere, upon which many of its most remarkable variations depend. Besides this, it was surrounded by a luminous nebulosity, which always exhibited the same brilliancy in every part of its surface, without any appearance of phases; from which circumstance he concludes, that this light being always equable, cannot be the effect of any reflection from the solar light.

Two different parts may be distinguished in the head of this comet: 1. A spherical nebulosity of a whitish coloured light, which surrounded the exterior nucleus, and which is supposed to depend upon the spontaneous luminousness of the body; 2. The posterior part opposite to the sun, beyond which was extended the double tail; this part was separated from the nucleus by a dark interval, equal to half the total diameter of the head of the comet. The apparent diameter of this head was 34′ 12′′, which gives it a real diameter of 2,052,000 geographical miles.

The greatest apparent length of the tail is 18°, which gives a real length of 131,852,000 geographical miles. M. Schröter conceives that we cannot explain this prodigious extent without admitting that there exists in space around the sun a subtile matter, susceptible of becoming luminous by the combined influence of the sun and the comet. Independent of the force which comets exercise as masses of matter, he conceives that they are endowed with a repulsive and impulsive force, which has some analogy to the electric fluid, and like it acts in different directions.

IV. Shower of Red Earth in Italy.

In the Annals of Philosophy, for Jan. 1817, there is a short notice of a shower of red earth which fell at Gerace, in Calabria; a number of the Giornale de Fisica of Brugnatelli, which we have just received,* contains a full account of the circumstance, with a description of the substance, by Sig. Sementini, Professor of Chemistry at Naples, of which the following is an extract.

It occurred on March 14, 1813: the wind had been westerly for two days, when at two p. m. it suddenly became calm, the atmosphere grew cloudy, and the darkness gradually became so great as to render it necessary to light candles. The sky assumed the colour of red-hot iron, thunder and lightning continued for a considerable length of time, and the sea was heard to roar, although six miles from the city. Large drops of rain then began to fall, which were of a blood-red colour.

Sig. Sementini collected a quantity of the powder which fell, and describes its physical properties to be as follows: It had a yellow colour, like canella; an earthy, insipid taste; it was unctuous to the touch, and extremely subtile. When the powder was moderately heated, it changed its colour, first to a brown, and afterwards to a black, and became red again as the temperature was raised; after it had been heated, many small shining plates were visible, it no longer effervesced with acids, and had lost about of its weight. Its specific gravity was 2.07.

Sig. Sementini then subjected the powder to chemical analysis, and found its composition to be as follows:

So large a proportion of loss was at first ascribed to some inaccuracy in the analysis, or to some body that had accidentally been mixed with the powder; but when he found it always to occur, whatever care was taken in the analysis, he began to suspect that it depended upon some combustible matter essential to the substance. This suspicion was afterwards verified; and by digesting the powder in boiling alcohol for a length of time, he obtained from it a greenish yellow colouring matter, which, when dried, acquired a pitchy consistence, was inflammable, and

* Dec. 2, tom. i.