REMARKS.

First Month.-21. A dripping day. 22. Nimbi grouped with other clouds: fine at mid-day. 23. Overcast. 24. Drizzling: rain in the night. 25. Overcast. 26. The same: a fog on the Thames appeared from hence to be a dense bank of cloud in the horizon: a little rain by night. 27. Fresh breeze: cloudy: p.m. a shower, with hail: night frosty. 28. Fresh breeze: drizzling rain: snow: fair, p. m. 29. Hoar frost: cloudy: fair. 30 Very white frost: misty horizon: sunshine after. 31. As yesterday, a. m.: at noon, hygr. 50°, the dust flies: wind S.W. p. m. with the usual sound for rain.

Second Month.-1. Hoar frost: fair. 2. Ice now about two inches thick: after hoar frost, a misty thaw: wet and windy evening. 3. Fair: moisture on the outside only of the windows. 4. Strong breeze at S.: misty: rain, followed by Cumulus, with Cirrostratus. 5. Very misty : the trees dripping. 6. Small and heavier rain by intervals: sleet at evening. 7. A gale from N. E., which came on last night, has brought a deep snow: snowy at intervals through the day. 8. A smart breeze,

with clear sunshine: the roads sloppy at mid-day: some distant clouds in the horizon at sun-set. 9. A continued sun-shine produced not the least effect on the ice to-day: hygr. at three p. m. 47°: there was a mistiness perceptible, to a certain height, round the horizon: the wind a gentle breeze. 10. For remarks on this night, see the sequel. 11. Hygr. as yesterday nearly: sleet, snow, and rudiments of hail, in minute quantity. 15. After three days of clear sky (a little Cirrostratus excepted), an extremely misty air: different clouds followed, and a few drops by inosculation. 16. a. m. Cirrostratus in flocks: wind changed to S.W., then to N.W., and blew strong at night: hygr. receded to 46°. 17. Frost on the ground, from evaporation merely: the air by two thermometers not below 33°: the snow mostly gone; but a very thick ice remains on the water: Cumuli rose this morning, and passed to large spreading Cumulostrati. 18. Obscurity to the N. E: snow, p. m. which melted in the night.

Mean of the hygrometer at nine, a. m. 80°. Rain and melted snow, 2.21 inches. A night on which Fahrenheit's thermometer remains for some hours below Zero, is, in this climate, a rare occurrence: probably not above five of them fall within a century; the last appearing to have been 19 years ago. It is observable that this extreme low temperature is not, as might be expected, peculiar to long continued frosts, but happens rather at an interval of one winter after such a season. Such was the frost of 1794-5, which lasted 44 days, one whole day's remission excepted, immediately before which the thermometer had descended to 2; but in 1796-7, I find a temperature recorded of 6, 5, with circumstances that indicate its having continued below Zero for some hours. Again, the character of the winter before last will be fresh in remembrance: the minimum of that season appears to have been not lower than 5°; and we have now a depression reaching

to

5. I do not, however, lay much stress on this analogy, which is pointed out rather for the use of future observers.

At

I was prepared to expect the intense cold of the night of the 9th to 10th instant, by the circumstance of a temperature of 7°, (or probably 5°) on the night before, being followed by a clear sky, with the wind at E, and a maximum for the day of only 20°. Early in the evening, on trying the experiment of placing a wet finger on the ironrailing without, it was found to adhere immediately and strongly to the iron. I exposed several thermometers in different situations. 8, p. m., a quicksilver thermometer, with the bulb supported a little above the snow, stood at Zero: at 11, p. m., a spirit thermometer in the same position indicated - 4; the former, which had a pretty large bulb, had not sunk below 3. At half past seven, a. m., the 10th, a quicksilver and a spirit thermometer, hung over-night about eight feet above the ground, indicated respectively 3, and were evidently rising. The minimum of 5, which I have registered, was taken from a Six's thermometer, the freezing point of which is very correctly marked on the scale, placed a little above the snow. the float of this thermometer had not room to move further, it may not have indicated the actual minimum of the air in that situation: but I have other evidence that, at the usual height from the ground, of my standard thermometer, the temperature was at no time below 5. The exposure is North, and very open.

As

From eight, a. m. the thermometer continued to rise steadily: at noon a temperature of 25° was pleasant, by contrast, to the feeling, and it was easy to keep warm in walking without an upper coat. Even at Zero, however, the first impression of the air on the skin was not disagreeable, the dryness and stillness greatly tending to prevent that sudden abstraction of heat, which is felt in moist and quickly flowing air. Early in the afternoon the wind changed all at once to S. W.; some large Cirri, which had appeared all the day, passed to Cirrocumulus and Cirrostratus, with obscurity to the south. I now confidently expected rain (as had happened in former instances) but was deceived; and the thaw has taken place with a dry air for the most part, and with several interruptions by night.

During these two days the barometer, which had risen rapidly, fluctuated between 29.6 and 29.7 inches, and immediately after resumed its course, and rose at the same rate as before.

The mean temperature of this period is precisely 32°, and it is remarkable, that the mean temperature of each of three similar periods of frost, comprehended in the long winter of 1813-4, does not vary a degree from 32°; though preceded and followed by periods which respectively exhibit a mean of about 44°. On examination, I perceive that this analogy might be extended further.

The gale at N. E. with which this frost came in, brought with it abundance of snow, which loaded the trees to their tops, and weighed down the smaller shrubs to the ground. The peculiar clinging quality of some snows merits inquiry. It is in part the result of the needly crystallized texture, aided by a degree of moisture attending, which afterwards freezes in the mass; but as light volcanic ashes have been found likewise to possess this quality, and in a still higher degree, perhaps we ought to attribute something to the electric charge with which each of these light bodies arrives at the earth. The seasonable covering which snow affords to the vegetable kingdom is matter of common remark; but it is not so generally understood in how great a

degree the very circumstance of its production abates the first rigour of the cold. Just before this snow the air was extremely moist; the snow cleared it of an inch and a half, nearly, of water, and it has since indicated considerable dryness. Now it is quite probable that the which afforded this water was found, by the supervening rapour N. E. current, diffused in our local atmosphere, and by it decomposed. In this case the whole of the latent or constituent heat given out by the vapour in passing to the solid state, must have gone to raise the temperature of that current. Hence a considerable interval, of gradually increasing cold, before we experienced its extreme effects; during which, too, the earth got provided with its accustomed covering.

After a copious fall of snow an observer may find, in the scenery which it forms, some things on which to exercise his powers of reflection. The pensile drifts, which in a mountainous country are objects of just alarm, may be contemplated, here, to discover the principles of their construction, and the manner in which they rest on so narrow a base. When the sun shines clear, and the temperature is at the same time too low for it to produce any moisture, the level surface may be found sprinkled with small polished plates of ice, which refract the light in colours as varied and as brilliant as those of the drops of dew. At such times, there are also to be found on the borders of frozen pools, and on small bodies which happen to be fixed in the ice and project from the surface, groups of feathery crystals, of considerable size, and of an extremely curious and delicate structure. From the moment almost that snow alights on the ground, it begins to undergo certain changes, which commonly end in a more solid crystallization than that which it had originally. A notable proportion evaporates again, and this at temperatures far below the freezing point. On the night of the 10th instant I exposed 1000 grains of light snow, spread on a dish, (which had previously the temperature of the air) of about six inches diameter. In the first hour after dark it lost five grains; in the second, four grains; in the third it acquired a grain, the wind having changed, and the temperature, which had been falling from 25°, inclining to rise again. The hygrometer was at 50°, with a gentle breeze at east. In the course of the night the total loss was about 60 grains. This evaporation from snow may very well supply the water for forming those thin mists, which appear in intense frost: and the slight increase during a part of the time, in this experiment, may throw light on the formation of the secondary icy crystallizations above-mentioned. It appears that the air in a still frosty night becomes partially loaded, either with spicule of ice, or with particles of water, at a temperature below freezing, and ready to become solid the moment they find a support. Hence the rime on trees, which is found to accumulate chiefly on the windward side of the twigs and branches.

As to those more copious mists, of the modification stratus, which accompany the setting in of long frosts, I conceive them to originate in part from the yet unfrozen rivers, and other waters, near which they are most abundant; in part from the moisture of the earth itself: for it is contrary to experience to suppose, that the frozen state of the surface can prevent the ascent of vapour from the porous soil below: which will continue to emit it, until its temperature becomes, by the gradual penetration of the frost, nearly on a level with that of the cold air then constantly flowing over it, though too gently to disperse the cloud formed.

Tottenham, Second Month, 20, 1816.

L. HOWARD.

1

ANNALS

OF

PHILOSOPHY.

APRIL, 1816.

ARTICLE I.

Biographical Account of the late John Robison, LL. D. F. R. S. E. and Professor of Natural Philosophy in the University of Edinburgh. By John Playfair, F.R.S. L. & E. &c.

(Concluded from p. 183.)

IN December, 1785, Mr. Robison was attacked by a severe disorder, which, with but few intervals of relaxation, continued to afflict him to the end of his life, and which, though borne with much resignation, and resisted with singular fortitude, could not but at length impair both the vigour and the continuity of his exertions. The disorder seemed to be situated between the urethra and the perineum. At times it was accompanied with the severest pain, and with violent spasms, which were easily excited. The disease, however, was only known by the pain produced; and never, by any visible or palpable symptom, gave information of its nature, as no change in the parts which were the seat of it could ever be observed. A complaint of this nature it is evident must have less chance of being removed than any other, and it accordingly baffled the art of the most skilful medical men both in Edinburgh and London.

Notwithstanding this state of suffering, his general health was not for a long time materially injured, nor the powers of his mind relaxed, so that he continued to prosecute study with vigour and steadiness. A malady which was both severe and chronical admitted of no palliative so good as the comfort of domestic society, which Mr. Robison happily enjoyed, having married soon after he settled in Edinburgh. The care and attention of Mrs. Robison, and the affectionate regards of his children, as they grew up, were blessings VOL. VII. N° IV.

R

to which, with all his habits of study and abstraction, he was ever perfectly alive.

This indisposition did not prevent him from engaging about this time in a very laborious undertaking. A work with the title of Encyclopædia Britannica, undertaken at Edinburgh several years before this period, was now undergoing a third edition, in which it was to advance from three to 18 volumes. Twelve of these had been already published, under the direction of the original editor, Mr. Colin Macfarquhar, when, on his death, the task of continuing the work was committed to the care of the Rev. Dr. Gleig, and about the same time Professor Robison became a contributor to it. He was the first contributor who was professedly and really a man of science, and from that time the Encyclopædia Britannica ceased to be a mere compilation. Dictionaries of Arts and Sciences in this island had hitherto been little else than compilations; and though in France the co-operation of some of the most profound and enlightened men of the age had produced a work of great merit and celebrity, with us compositions of the same class had been committed to the hands of very inferior artists. The accession of Professor Robison was an event of great importance in the history of the above publication.

It was in the year 1793 that he began to write in this book, and it was at the article Optics, with him a very favourite science, that his labours commenced. From that time he continued to enrich the Encyclopædia with a variety of valuable treatises, till its completion in 1801.

The general merit of the articles thus composed makes it difficult to point out particulars. Those in which theoretical and practical knowledge are combined are of distinguished merit; such are Seamanship, Telescope, Roof, Water-works, Resistance of Fluids, Running of Rivers. To these I must add the articles Electricity and Magnetism in the Supplement, where the theories of pinus are laid down with great clearness and precision, as well as with very considerable improvement. In ascertaining the law of the electric attraction, his experiments were ingenious, as well as original, and afforded an approximation to the result which the great skill and the excellent apparatus of Coulomb have since exactly ascertained. In the Supplement is also contained a very full account of the theory of Boscovich; a subject with which he was much delighted, and which he used to explain in his lectures with great spirit and elegance.

These articles, if collected, would form a quarto volume of more than a thousand pages. I am persuaded that when brought together, and arranged by themselves, they will make an acceptable present to the public; and I have the satisfaction to state that such a work is now preparing, under the direction of an editor whose remarks or corrections cannot but add greatly to its value. Notwithstanding the merit which the separate articles possess, they are not entirely