Earthquakes in Manchester, Wednesday, November 18th, 1795.

The slight shock of an earthquake, felt on this occasion, appears to have produced a sensation very similar to that on Friday morning last, a gentle heaving-up of their bed. We copy the following notice of it from "Harrop's Manchester Mercury" of November 24, 1795:

"Several of the inhabitants of this town were greatly alarmed, on Wednesday night, between eleven and twelve, by the shock of an earthquake. The sensation it occasioned seemed to those retired to rest, as though a person in getting from under the bed had gently heaved it up. We do not hear of the smallest damage occasioned by it. The weather here has, for some days, been uncommonly variable. On Thursday, in the afternoon, there was a severe fall of snow, and Friday we had a sharp dry frost. At Nottingham, so severe was the shock, that the bells in the churches were awfully heard to sound in the steeples; several chimneys thrown down, &c.; but we have not yet heard of any material damage. It was so severely felt at Childwell, in that neighbourhood, as to throw down a stack of chimneys belonging to Thomas Carlton, Esq., of that place. Its direction seemed to be from N.E. to S.W. The same was also felt at Doncaster, Stamford, Leicester, Derby, Sheffield, and several other places."

Thursday, August 20th, 1835.

It is remarkable, that the principal shock on this occasion (as experienced at Clitheroe) was preceeded, as in the case of the earthquake on Friday last, by a slight shock, in the former instance about three hours and a half previous. The first shock was about midnight, on the 19th; the second about half-past three o'clock in the morning of the 20th August, when a rumble like distant thunder was immediately followed by a violent shaking of doors, windows, furniture, &c. At Lancaster it threw down a chimney; and it was also felt with considerable violence at Whitehaven, Ulverstone, Kendal, Garstang, Preston, and Blackpool. It was experienced, but in a very slight degree, in Manchester and the immediate neighbourhood, more particularly about Cheetham Hill and Kersal Moor. It appears to have extended from Carlisle on the north, to the borders of Cheshire on the south, and from the seacoast on the west, to the Yorkshire hills on the east; and to have been most violent at Lancaster, which is nearly halfway between the two extremes. The air was calm and serene, but, as on Friday morning last, quite warm, indeed sultry. It is remarkable, that this earthquake was preceeded by an occurrence of the same kind, a few days previous in Gloucestershire and Wiltshire.

Tuesday, June 11th, 1839.

This shock, which was felt about a quarter past eight o'clock in the morning, is also said to have been preceded by a very slight shock at an earlier hour. It was experienced as far north as Clitheroe, and as far south as Manchester, but does not seem to to have been felt westward of a line drawn from Manchester to Blackburn, nor does it appear to have extended eastward beyond the range of hills which separate Yorkshire from Lancashire. It was felt at Burnley, Bacup, Rawtenstall, Blackburn, Haslingden, Edenfield, Bury, Rochdale, and Manchester; but it was not felt, or but slightly, at Oldham or Ashton-under-Lyne. It was more violent at Bury, Rochdale, and Heywood, than in any other quarter. At Heywood some shafting was thrown out of gear by the vibration, and a quantity of china was broken in a closet; at Rochdale a wall was slightly damaged; and at Bury many articles were thrown down from shelves and chimney pieces. Cotton-factories, and other lofty buildings, were so violently shaken, that the hands rushed out in some instances, supposing that the building was falling. Throughout the whole range of its operation. it was attended by a hollow rumbling sound, like distant thunder. In the immediate neighbourhood of Manchester the shock was very little felt, being chiefly perceived by a tremulous motion, like the effect of a heavily loaded cart passing an unstable house. As in the case of the earthquake of August, 1835, this was proceeded by another in the West of England: in this case, an earthquake was experienced on Wednesday the 22d May, at Bridgewater and other places in Gloucestershire, along a tract of about sixteen miles in a straight line; where its effect was as if a heavy blow from beneath had been struck against the ground or floor accompanied by a peculiarly dead, but loud, report and the violent agitation of doors, windows, &c.

On Friday morning, the 10th March, 1843, the shock of an earthquake was felt in Manchester and the adjoining district, about twenty minutes after eight o'clock in the morning. The centre of this shock, which was but slight, appears to have been amongst the range of hills which border Yorkshire and Lancashire. No very important particulars have been observed to attend this earthquake. Another earthquake visited Manchester and an extensive range of district on every side, at about ten minutes before one o'clock on the morning of Friday, the 17th of March, 1843. It is curious to observe, that in this case, as in that on Aug. 20th, 1835, a preliminary shock, an hour before the principal one, was distinctly observed. The weather, previous to Friday, had been very cold, with disagreeable easterly winds; but a few hours before midnight of the Thursday preceding the shock, the air became exceedingly warm and sultry, though the thermometer did not rise proportionately to the heat experienced. The barometer fell about two-tenths of an inch

between the evening and midnight of Thursday the 16th, and the next day was perfect summer. The thermometer, rose to nearly 70° in the shade; the sun shone almost uninterruptedly the whole day; but, on the day following we had winter once more-easterly wind, fog, and all the disagreeables generally attending them. Sunday, the 19th, was fine, though cooled by an eastern breeze, Monday morning indicated an electric storm, and in the afternoon, about three o'clock, it came on in grand style: lightning, thunder, and. heavy rain, in great abundance.

There is something very remarkable in the coincidence of the atmospheric electricity subsequent to the earthquakes in 1777, and of March 17th, 1843; which leaves us to conjecture that electricity has something to do with these English earthquakes. There is another peculiarity in these phenomena. They seem to be displayed within the great area of geological fault, between the the two principal chains of hills, and the greatest effect appears to have been in the axis of this fault. Should this prove to be the case in all instances of earthquake in the midland and northern districts of England, may we not suppose, that the great fault, itself has been effected by an earthquake?

This earthquake extended northward into the borders of Scotland, and southward into Wales. At Liverpool, it was more violent than in Manchester; and at Lancaster, even more so than in Liverpool. In some places two distinct shocks were felt, and in others even three are said to have occurred. A subterraneous rumbling noise, somewhat like distant thunder, is said to have been heard in some places, whilst in others no such noise was heard. Persons awake and sitting up in Manchester never felt the shock, whilst others in bed, in the same house, thought their beds were lifted up as if by a strong man beneath each of them.

Since Monday last, the 20th, the weather has been cold, with easterly winds; and on Saturday, yesterday, and to-day, the 27th, the east wind has been unusually strong, and excessively cold to the senses, although the thermometer now stands at 40.°

Manchester, March 27th, 1843.

On the Distribution and Retention of Magnetic Polarity in Metallic Bodies. By W. STURGEON, Lecturer on Experimental Philosophy at the Honourable East India Company's Military Academy, Addiscombe.*

THE retention of magnetic polarity in hardened steel is so very strikingly manifested in artificial magnets of various forms, and the circumstance is so well known, that it would be quite unnecessary in this place to advance any remarks concerning it, further than merely to name it, for form sake, in the order in which it stands, and the pre

* From "The Philosophical Magazine," of April, 1832.

eminent rank which it universally holds amongst the metals, as to the display of this mysterious faculty.

The retention and distribution of magnetic polarity in other metals, however, are by no means of such general notoriety; peculiar modes of experimenting are required for their exhibition, and but very few of their phenomena have yet had recognition beyond the sweep of the curious eye of the philosopher.

In my last communication I had occasion to allude to the retention of magnetic polarity (or the residual polarity, as I there called it) displayed in soft iron, which had previously been excited to an exalted degree of intensity. My remarks in that communication, however, were confined to soft iron in bars, in the various forms in which it is usually employed as electro-magnets. In the present, my observations will be extended to the retention, and also to the distribution of magnetic polarity in thin sheet-iron, and other metallic bodies, when in the shape of discs.

The distribution and retention of magnetic polarity in thin discs of soft iron by rotation, when placed in various positions, with reference to the magnetic meridian, &c., were first noticed and investigated by Mr. Christie, in an extensive series of highly interesting experiments which were published in the " Phil. Trans." for 1825.† Mr. Christie very politely showed me several of his experiments at the time he was carrying them on; and when published, presented me with a copy of the paper in which they were described. In a very short time afterwards I repeated some of those experiments with a temporary apparatus which I fitted up for the purpose, and obtained the most satisfactory and corroborative results. Besides repeating the original experiments, however, I was led by curiosity to institute others, which, as some of the results are rather curious, I now propose to detail.

Exp. 1-Let a bed, (Plate II., Fig. 1), represent a disc of sheet-iron, about fifteen inches in diameter, placed south of, and in the same horizotal plane as the needle n's, with its centre in the magnetic meridian; and a neutral point a, in its northern edge, about one inch distant from the pole n.

If the north pole of a powerful bar magnet, having its axis vertical, be now passed over a diameter of the disc from c to a, as indicated by the arrow, and about half an inch above it,§ and taken away suddenly from the point a, the plate will exhibit south polarity at that point; and the pole n of the needle will be attracted with a considerable force. If now a small delicate dipping needle be carried gently over the surface of the plate, feeble poles of both cha

See last Number of the "Annals."

† Mr. Christie's paper was read before the Royal Society, May 12, 1825. That pole of the needle which is solicited by the southern parts of the earth is here called north.

§ A round piece of board of the same diameter as the iron plate, and of a proper thickness, I have found very convenient to prevent the magnet from touching the plate.

racters will sometimes be found in various parts of the iron, varying in power and situation almost every time the magnet repeats the excitation; but in no case will a north pole be found of equal vigour with the south pole determined at the point a. In several instances I have found no regular pole only at a; all the rest of the plate exhibiting a diffused polarity without any apparent central pole. It sometimes happens, however, that all the south polarity of the plate is separated from its north polarity by an irregular curve line, as represented by the dotted line e q (Fig. 1), which line may be regarded as a magnetic equator; every part of the plate on n side of that line being north polar, and all that part on s side of the line e q being south polar; s the situation of the principal pole.

Exp. 2. Let the north pole of the magnet be carried once round, and just within the edge of the disc, at the same distance above it as before, and in the direction of the arrows (Fig. 2), commencing and terminating the revolution at the point a, and suddenly quitting it as before.

The plate will again exhibit polarity; but the north pole of the needle, when reconciled, will be deflected towards the west, as n' s (Fig. 2), showing that the attracting pole is situated in the limb a d.

Exp. 3.-Let the same pole of the magnet be now carried round the plate in the opposite direction, from the point a to the same point again, quitting a as in the last experiment. The north pole of the needle will now repose towards the east of the magnetic meridian, indicating the attracting pole to be in the limb a b, Fig. 3.

It appears by the phenomena exhibited in the last two experiments, that there is a peculiar distribution of magnetic polarity by passing the pole of the magnet round the edge of the disc, differing considerably from that occasioned by passing the pole over a diameter. There is, however, as decided a regularity in the distribution of polarity by this process as by the former; for, although the point last excited be not determined in the point a where the magnet quits the plate, its position is invariably found in that limb which was last passed over by the magnet. The other species of polarity is diffused over a great part of the area of the plate, without any apparent determinate pole.

The north pole of the magnet when first brought over the edge of the disc at the point a, excites south polarity in the iron immediately beneath it; in which point the disc would remain polar, if the magnet were to be withdrawn without passing over any other part of it. When, however, the pole of the magnet is permitted to pass round the plate, the parts over which it passes will become polar in succession, and the point a will receive the terminal exciting impression.

Now, as every point near to the edge of the disc may be supposed to be equally disposed to retain polarity, it is evident that as the exciting pole proceeds in its revolution, the successive poles which it generates will have an equal tendency to a permanent habitation : but in the same gradual succession as the exciting pole abandons them, and calls forth others in its progress, the primogenial poles