out of the ponds. In a great drought, provision ought to be made, to keep the water at the same height as it commonly stands in the pond, i. e. between 4 and and 5 feet. If the water stagnate and grow putrid, it must be let off, and a supply of fresh water be introduced from the reservoirs. If the weeds, especially reed and flags, and some of the aquatic grasses, over-run too much the pond, scythes fixed on poles of 16 or 20 feet, with a lead fastened to them to keep the scythes on the bottom of the pond, are thrown out, and then again drawn to the person that works with them, by which the weeds will all be cut; after which operation, they must be drawn up by long harrows, and laid in heaps on the shore for putrefaction, and in length of time, for manure. This cleaning of ponds must never be done in a spawning-pond, where it would be the destruction of thousands of fish.

Autumn is the best season for catching such carp as are intended for the market. After the pond has been for 5 or 6 years in constant use, it is likewise time to let the water entirely off, and clear the pond of the mud, which often increases too much, and becomes a nuisance. When the pond is dry, it may be ploughed before the frost sets in, and next spring oats or barley should be sown in it, after a new ploughing; and it will repay the trouble to the owner with a rich and plentiful crop. When the loose superfluous mud is carried-off out of the pond, care ought to be taken not to take the soil below the original level of the pond. Some people sow a pond, which has been laid dry for some. months, with oats; and when growing, they fill the pond with water, and introduce carp for spawning, and think, by this contrivance, to procure food for the fish and something to rub their bellies against. But this practice seems to be more noxious than beneficial; for the growing oats will putrefy, and communicate putridity to the water, which can by no means be salutary to the fish.

The epicures sometimes feed carp, during the colder season, in a cellar. The following method is the best that can be observed for that purpose. A carp is laid on a great quantity of wet moss, spread on a piece of net, which then is gathered into a purse, and the moss so contrived, that the whole fish is entirely wrapt up in it: however, care must be taken to give the fish ease, and not to squeeze it, so that it may have room to breathe in this confined attitude. The net with the fish and moss is then plunged into water and hung up to the ceiling of the cellar. In the beginning, this operation must be very frequently repeated, at least every 3 or 4 hours; by length of time the fish will be more used to the new element, and will bear to be out of water for 6 or 7 hours.* Its

* It is known to every one that a carp will live a great while out of water; but perhaps it may not be so notorious, that the keeping him several hours in the common air, without any precautions, may be repeated from day to day, without any apparent inconvenience to the fish. There is a fishmonger near Clare-market, who in the winter exposes for sale a bushel at least of carp and tench,

food is bread soaked in milk, which in the beginning must be administered to the fish in small quantities; in a short time the fish will bear more and grow fatter. Mr. F. saw the experiment tried in a nobleman's house, in the principality of Anhalt-Dessau; and during a fortnight he visited the fish every day. After the fish had been kept in the above manner during a fortnight, it was dressed and served up at dinner, when every one present found it excellent in its flavour.

XXXVIII. Of the Remarkable Cold observed at Glasgow, in the Month of January 1768. By Mr. Alexander Wilson, Professor of Astronomy at Glasgow. p. 326.

While in bed, on Sunday morning, Jan. 3, 1768, about 8 o'clock, Mr. W. felt unusually cold. A little while after, on reaching out for a decanter which he placed near him the preceding night, with some water in it, he was surprized to find the surface of the water frozen over, the like not having happened before in that place. On this he desired his son to try the cold by a thermometer. The experiment was soon after made, by exposing a thermometer at a high north window, and free from the walls of the house; in which situation it had not remained a quarter of an hour, when they found the mercury had fallen to 5o of Fahrenheit's scale. Being satisfied, by another thermometer, that there was no fallacy in this preliminary observation, it naturally occurred, that the cold, however intense it now was, might have been much more so at some earlier hour of the morning. But how to ascertain this, and to recover the lost observation, was the difficulty. In the eagerness of disappointed curiosity, they were disposed to magnify this golden opportunity, which had now escaped them, and to reflect on it with regret, when luckily a little invention helped them out. A notion suggested itself, that if they went very warily to work, they might perhaps surprize those imagined colds still lurking under the surface of the snow, which at that time lay thick upon the ground.

Mr. W. immediately repaired to the fields, and sought out a low place, on which the sun had not then risen; here he laid the thermometer in the snow, almost on the very surface, when presently the mercury sunk from + 6 deg. to -2 deg., which therefore he concluded to have been pretty nearly the coldest temperature of the air over night. The next thing was, to make regular observations with the thermometer, so long as the cold promised to continue remarkable. The instrument was hung upon a pole near the observatory, and to

in the same dry vessel: but a small proportion of these can be sold in a day; and I have frequently been informed, that the fish continue in good health, notwithstanding their being thus exposed to the air 6 cr 7 hours for several successive days. D. BAR.-Orig.

the windward of it, care having been also taken to keep it under a proper shade, so long as the sun shone out.

Register of the Thermometer, kept at the college of Glasgow, on Sunday, Jan. 3, and Monday Jan. 4, 1768.

Sunday 10 o'clock + 5 deg. morning 11

12

7

9

10

afternoon 1

2

11

3

9

3

63

48

5

5

61

7

71

8

9

3

2

1

2호

It was observable, that after The temperature of the snow sun setting, the atmosphere had on Sunday morning, at about a tendency sometines to turn a ten inches below the surface, little foggy, and again quickly

was near to 30 deg.

to clear up, balancing as it were between these two different states. It is worthy of notice, that the minute variations of the thermometer, as set down in the above register, seemed to depend on these different constitutions of the air; the mercury al03 ways rising in the thermometer a small matter, when the mistiness came on, and vice versa.

In the intervals of observations, they made some other experiments, which the present intensity of the frost suggested; particularly one relating to the evaporation of ice, which was tried in the following manner. Mr. W. took a square reflecting metal belonging to his 2of foot telescope, and exposed it on the ballustrade of the observatory, till it had acquired the temperature of the place, which was then at 0 deg.: after it was thus cooled, he breathed on it repeatedly, till its polished surface was covered over with an incrustation of ice or frozen vapour, of a very palpable thickness. In this condition the speculum was replaced in its former situation, having its incrusted surface exposed to the still open air, when, in a little time, they found the frozen pellicle beginning to disappear at the outer edge, all around, leaving the metal quite clear. Gradually more and more of the speculum was bared in a regular progression, from the circumference towards the centre; and at last, in about 50 minutes, the whole surface had parted with its ice. This experiment was repeated when the speculum was defended from the open air, by a large thin box, with a cloth over it. The event turned out the same as before, only it required longer time.

41

5

This progress of the evaporation, from the outer parts towards the centre of the speculum, was probably owing to the original plate of ice being thickest towards the centre, a circumstance which might arise from the manner of fixing it at first breathing on it. Or perhaps it may be imputed to some more curious

cause, and may be some effect of the repulsive force belonging to the polished surface; but this point they did not sufficiently examine into, by a due repetition of experiments. Mr. W. just mentions, that partly with a view to this matter, they exposed as above, a set of bodies, having their surfaces of different degrees of polish, and as equally covered with frozen moisture as they could julge. The result of which experiments seemed to favour the idea of the ice being less attached to the more polished surface than to the coarser. This appeared particularly in the case of a comparison made between the speculum above mentioned, and the brass end or cover of the same telescope; for the ice was found still to cleave to its surface a good while after the speculum was entirely cleared.

XXXIX. Some Experiments on Putrefaction. By F. L. F. Crell, M. D., and Professor of Chemistry at Brunswick.

p. 332.

The celebrated Lord Bacon (Nat. Hist. Cent. 4.) has doubtless shown a very great sagacity, in pointing out to posterity, putrefaction, as a subject worthy of being further inquired into; and as there happen daily so many changes, not only in the inanimate, but also in the animate world, carried on by its means; the knowledge of every thing relating to it must clear up a great many points in natural philosophy, not thoroughly understood before. But these inquiries ought to be of still more consequence to mankind, as health depends, greatly on keeping in due bounds putrefaction, which the body naturally tends to. For these reasons, Sir John Pringle deserves, besides his other eminent merits, very great praise, on his having made many experiments on this subject; and medicine is indebted to him for considerable improvements resulting from them. He has besides opened the way to many other gentlemen, among whom excel Dr. Gaber, and Dr. M'Bride, whose numerous experiments show the ingenuity and sagacity they are possessed of: but the subject is not yet exhausted, nor will it be very easily. I have made some experiments relating to it; and should be very glad if they threw a new light on some points of the greatest importance to medicine.

Dr. Gaber has proved, by his experiments, the presence of a volatile alkali produced by putrefaction; but as he did not discover by the same proceedings * any in its beginning or end, though there was a very putrid smell, he denies its existence in these states, and concludes that this volatile alkali is not a necessary product of putrefaction. This doctrine seemed not quite conformable to the

• Acta Taurinens. vol. i. p. 78. Cum attegerint summum effervescentiæ gradum, continuato ejusdem loci calore effervescentiæ vim amiserunt. P. 79. Citius plerumque prodiit foetor, quam alkali, idemque tardius desiit. P. 82. Massam inde relinqui foetentissimam, sed emisso alkali ad effervescentiam ineptam.-Orig.

+ Id. p. 83, 15. Quum foeteret gravissime residuum destillationis, quamquam omni alkali orbatum, manifestum videtur, ab alkali foetorem exaltari quidem posse, et magis penetrantem effici, non

phenomena: for as all smell, as much as we know at least till now, depends on a saline matter, joined with a phlogiston, and the saline matter producing the putrid stench, was not very likely an acid; I supposed it to be a volatile alkali, which involved in phlogistic matter might fly off, before the alkali was developed. I wanted to know, by experiment, if I was right; for this purpose I put, the 19th of June (the thermometer being 58° of Fahrenheit, and continuing between 58° and 62° all the time I observed), in a pretty large receiver, some beef cut in - very small pieces; I covered the bottom with it thinly, and poured upon it water, about 2 inches high. The 22d, the putrid smell was very sensible: but I let it stand till the 24th, when I poured off the fluid, adding again about the same quantity of water to the flesh. I filtrated then the fluid through a piece of fine linen, and mixed with some of it the syrup of violets, which it did not alter; neither did it effervesce with the spirit of vitriol, diluted to a sharpness near that of the vegetable acid. I thought of keeping it in digestion for some days; but for fear that some little solid particles might have passed through the linen, and by that means, in growing putrid, might give some alkali, and render the trial inaccurate, I distilled the fluid by a heat of about 160°, after which I repeated the trial with the syrup of violets and the spirit of vitriol; but it produced no change. I then put it, the 25th, into a retort, fitted to it a receiver, applied to the jointure a ring of paste made of flour and water, covered it with a piece of wet bladder, and exposed it in a balneum arena to a heat of 108° to 116°, till the 29th of June, when the whole fluid was distilled over. I perceived during this operation, that the liquor, from being quite transparent, became turbid; the first distilled transparent fluid grew also turbid in the receiver, and at the bottom of the retort there was a small settlement of a whitish earth. The liquor had a particular smell, but quite different from a putrid one, inclining to the volatile alkali; and showed a slight but sensible degree of effervescence with the spirit of vitriol; and the syrup of violets was turned evidently green, by it.

In the mean time, the flesh with the water continued to emit a putrid stench; and the 28th of June I found the fluid colouring the syrup of violets greenish, and showing a kind of effervescence with the acid. Both these qualities were autem ab eodem produci, quandoquidem superest eo sublato-16. Videtur is odor a volatilibus admodum particulis proficisci, sed quæ ab alkali dissimiles sunt, plerumque citius gignantur, tardiusqué dissipentur-alcalescentia adesse potest modico foetori conjuncta-vicissim maximus foetor absque alcali-Ex quibus differentia inter foetidas alcalinasque partes confirmari videtur.-P. 84, 17. Videtur alcali non esse productum necessarium putrefactionis neque gradum alcalescentiæ gradui putrefactionis respondere.-Orig.

It requires some attention to find out the proper time when to pour off the liquor; if it be done too soon, it will give too little volatile alkali to be much sensible by experiments; for thoughi, smells strongly, it is known how little matter is required to produce a strong smell. If it is delayed too long, it shows already signs of an alkali. For that reason, I made many experiments in vain.Orig.