accurately, I procured a standard thermometer, by Messrs. Troughton & Simms. I placed it in the same situation, and made several observations in the day, for some weeks, in the spring of the year, when the range of the thermometer is the greatest. After I had got the scale properly divided, I engraved it on a plate of copper, in order to get a number of copies printed. The only attendance the instrument now requires, is to put a fresh paper upon the cylinder, by means of stretching screws fixed on one side of the cylinder, once a week, when I wind the time-piece up.

A, copper bar, one inch in diameter, and ten feet long; B, cast iron trough, to which the copper bar is made fast at the bottom; C, brass cap. soldered fast to the copper bar, with knife edges on the under side, which rest on the tubular end of the first lever D, its fulcrum rests on the upper end of the cast iron trough B; E, flanges to bolt the trough to the outer side of a wall, near the angle of a room; F, part of the cast iron trough which passes through the wall into the room, carrying the fulcrum of the second lever I, and to which the revolving cylinder G is fixed; H, a weight to keep the first lever D steady on its bearings, and to counterpoise the second lever I; K, tracing pencil; L, a screw working in the edge of the wheel M, and coupled to the minute hand of the time-piece, making one revolution in an hour; the wheel M is fixed to the axis of the cylinder, and has 192 threads cut in its edge, and would make one revolution in eight days; N, a binding screw, to adjust the pencil to the proper hour line, when a fresh paper is put on

once a week; O, brass rings, made fast to the cast iron trough, to keep the copper bar steady, but through which it can move; the dotted line shows the side of the iron trough.

The instrument acts by the difference in the expansion of copper and iron, that difference being multiplied about 120 times, by a compound lever. The scale was obtained by placing in the same situation a standard thermometer, by Messrs. Troughton & Simms, for several weeks, in the spring of the year, when the range is the greatest, and making a great number of observations each day.

Tabulated results for the year 1847, taken from tracings by the Instrument described.

Prof. Lloyd observed, that he much feared, as the indications of this thermometer were derived from the unequal expansion of different metals, magnified by a system of levers, that the bearings of the levers would be found not to move continuously, but by starts.

Sir W. S. Harris thought it likely some correction would be required for the hygrometrical state of the paper on which the curves were traced, as well as for the effects of changes of temperature of other parts of the instrument.

Prof. Lloyd, having been requested, by several members, to describe a barometer on a new principle which he had lately seen, said that it was a French invention. A cylinder of copper, with a very thin and corrugated end, was partially exhausted and hermetically sealed; and the effect of the varying pressure of the atmosphere, on the thin end, was magnified by a system of levers, so as to affect the index of a dial, very little larger than a watch dial. A friend of his had tested the indications of the instrument, by placing it under the receiver of an air pump, and observing its march, in comparison with the indications of the long gange, and found them to agree to less than the 1-100th of an inch. Mr. Jenkins mentioned some remarkable cases of the discrepancy of the indications of a number of compared thermometers, ranged along a wall at short distances, and at intervals of a quarter of an hour.

Ibid.

On some New Relations of the Diamagnetic Force. By PROF. PLÜCKER. Mr. Plücker gave a short account of experiments belonging to a new magnetic action. A crystal with one optical axis, being brought between the two poles of a magnet, there will be a repulsive force, going out from each of the poles, and acting upon the optical axis. According to this action, the crystal, if suspended, will take such a position, that its optical axis is placed within the equatorial plane. When the

crystal has two optical axes, there will be the same action on both; according to which, the line bisecting the acute angle formed by the axis will turn into the equatorial plane. When the crystal is suspend- · ed in such a way, that it may freely move round any line whatever of the plane, containing both axes, this plane will take the equatorial position. Thus a crystal, being neither transparent, nor showing any trace of its crystaline structure, we may, by means of a magnet, find the optical axes. At the same time we get a new proof of the connexion between light and magnetism. When light is passing through a crystal, there are in general two directions, where it is effected in a quite distinct way,-these same directions are acted upon by a magnet. Prof. Faraday contrived to convert two raw potatoes into representatives of the poles of an electro-magnet, and, by a slice of another, with a quill stuck through it, represented the magnetic or diamagnetic crystal with its optic axes-and thus contrived to convey a distinct idea of the exact results of Prof. Plücker's discoveries of the relations of the optical axes of the magnetic and diamagnetic crystals, and the changes of distance, to the nature and laws of the attractions and repulsions exhibited under the several circumstances detailed.

Sir W. S. Harris considered that the laws of magnetic forces, in relation to the action of magnets on each other, or a magnet on a mass of common iron, were liable to vary, from the changes which arose in the amount of inductive action of which the attracting bodies were susceptible. He had shown, in a paper in the Edinburgh and London Philosophical Transactions, that, in electricity and magnetism, the amount of inductive disturbance was limited,-so that, after a certain time, under given conditions, the disturbance became the greatest possible, and then the law of the force changed; and hence arose all the irregularities which had embarrassed early inquirers into the subject. In fact, the force between a magnet and a simple mass of iron varied in a simple inverse ratio with the force induced in the iron, and with the disturbance conjointly. If either of them became constant, the whole force varied with the other. If, therefore, it should happen that, as the disturbance in the iron approached a limit, the changes were not uniform, then we obtained irregular results. So long, however, as the induced force went on uniformly, we had the total or absolute force in the inverse ratio of the squares of the distances. In the case of two magnets magnetized, or nearly so, the force of attraction between them varied in the inverse ratio of the simple disturbance, because the amount of the induced force had been reached. On this principle it was found, that in the repulsive force between the two magnets, the repulsive action at certain distances became changed into attraction; and it is not an uncommon circumstance, to find two magnets attract at one distance, and repel at another.These results, he thought, might be applied in explanation of some of the phenomena now under consideration. The force of magnetic action might vary, whilst the diamagnetic force, after all, may have been

constant.

Dr. Lloyd inquired if Prof. Plücker had tried whether crystals with

positive axes, exhibited any difference in the laws of diamagnetic action, from those which had negative axes?

Prof. Faraday replied, that Prof. Plücker had minutely investigated this point, and found no diversity of law corresponding to this difference in optical structure.

Sir D. Brewster inquired whether Prof. Plücker had investigated the influence which changes of temperature produced in the diamagnetic action of crystals? Some of these changes, he conceived, were of such a nature as to afford an admirable test, whether the same circumstances in the corpuscular constitution of the crystal, on which their optical characters depended, were those which gave rise to their diamagnetic relations, or not. For example, in some of the biaxal crystals, as sulphate of lime, when heated, the axes approached, and at length coincided, the crystal becoming monaxal; and by continuing the heating, they again separated in a plane at right angles to the one in which they before lay. Such a series of changes, he conceived, if examined in relation to the diamagnetic forces, might afford a test whether the curious properties discovered by Prof. Plücker, had their origin in the chemical constitution of the bodies, or in that corpuscular structure from which their optical properties originated.

Prof. Plücker replied, that he had not tried the class of experiments pointed out by Sir D. Brewster; but he admitted their importance, and expressed a determination to pursue the inquiry.

Prof. Grove inquired whether the experiments were tried with the crystals placed in vacuo?

Prof. Plücker replied no; but in every case they were suspended either in air or in water.

Prof. Grove pointed out the necessity of caution in that case, as it was well known that differences between the diamagnetic actions of suspended bodies, and of the surrounding medium, would sometimes mask, and even reverse the action.

Prof. Faraday pointed out the precautions which had been taken to avoid this source of error.

Ibid.

On the Submergence of Ancient Land in Wales; the Accumulation of newer Strata around and above it; and the Re-appearance of the same Land by Elevation and Denudation. By PROF. A. C. RAMSAY.

This communication was illustrated by a section, on a true scale, of the rocks near Builth, in Radnorshire, where the Wenlock shales rest unconformably on the Llandeilo flags. The lower rocks must have been elevated previously to the formation of the upper, and their upturned edges must have been worn away by the sea, when the upper rocks were deposited, or previously. No power is known to exist far below the level of the sea, by which this process could have been effected; it must have taken place at the sea's level.

Throughout Wales, the Lower Silurian rocks appear to have been disturbed at one particular period-to have been heaved above water, and formed a coast, around which the succeeding rocks were accumu

lated. Near Bishop's Castle, the upheaval of the Llandeilo flags was followed by the deposition of the Caradoc sandstone, which is full of pebbles of the older rocks. After this, a subsidence appears to have taken place, the area of the sea was increased, and the Wenlock shale was deposited, not only over the Caradoc sandstone, but beyond it, as at Builth, upon the Llandeilo flags; and in some places the shale rests on Greenstone rocks, and certain pebbles from it, being in fact a gravelly sea bottom. This depression of the bed of the sea continued also during the deposition of the Ludlow rocks, which are conformable to the Wenlock shale; and there is no marked alteration in the organic remains of the two rocks. The Wenlock shale is 1500 feet thick, and the Ludlow rocks 3500 feet; and as it is certain that their organic remains could not have existed at the depth of 5000 feet, we must suppose a gradual subsidence of the area, such as is believed to be now taking place amongst some of the coral islands, until 5000 feet of rocks was accumulated over what had been dry land.

The old red sandstone, which has a maximum thickness of 8000 feet, appears also to have extended over this country, judging by the outliers, at a considerable distance to the north and west. Subsequently, the whole of this series, from the Caradoc sandstone upwards, was removed, and the ancient Silurian strata became the surface of dry land, as they had been so long before.

It now became a question, what amount of alteration may the Silurian rocks have undergone, during the time they were so covered up? If the same laws regulated the ascent of the internal temperature as at present, namely, 1° for every 54 feet, then the addition of 5000 feet of rock would have raised the temperature by 92°, whilst 9000 feet would have added 160°, and with 11,000 feet of superincumbent strata, the Lower Silurian rocks must have endured an increased temperature of 212°. To influences of this kind may, perhaps, be attributed the crystaline or metamorphic condition of some of the more ancient rocks,as suggested by Sir J. Herschel, in a paper communicated years ago to the Geological Society of London.

The Dean of Westminster referred to the Portland rock, in which a bed of vegetable soil occurs, full of trunks of trees, and cycadites; this bed rests on limestone containing ammonites, and is covered by similar marine deposits. Again in the Weald, fossil forests, and beds of freshwater shells are found above marine accumulations, and followed by the greensand and chalk. At the present time we find peat, and antiers of the red deer, in the bed of the channel, several miles off Swansea. On the Norfolk coast, and in the English Channel, are found the bones of the elephant, and fossil wood, disinterred from former cliffs by the action of the sea. These, with many other circumstances, were quoted as showing that, whilst the sea-level was fixed, the land had suffered depressions and elevations at many periods of time.

Prof. Phillips pointed out the extent of some of these subsidences of the land; for example, the old red sandstone, 8000 feet thick, all formed in shallow water, and the coal measures 11,000 feet thick, and added under similar circumstances; and inquired what condition of the interior of the earth can have admitted of the gradual subsidence of such great masses of strata? According to Mr. Hopkins's statement,