In determining the intensity of the magnetic force, a magnet was employed to draw a needle to the horizontal position. The magnet was then removed at an observed moment, and the needle permitted to oscillate till the arcs became too small to be observed. At every tenth vibration, both the arc and time were noted. The azimuth compasses employed by Captain S. to determine the magnetic variation were made upon Captain Kater's improved plan. The observations were generally made upon the ice, to avoid the great irregularities produced on board by the iron of the ship. The results of the different classes of observations were arranged in a tabular form.

March 4.-A paper was read by Dr Brewster on the action of crystalliz ed surfaces on light. Malus has remarked, that the action exerted upon light by the first surface of Iceland spar is independent of the position of its principal section; that its reflecting power extends beyond the limits of the polarising forces of the crystal; and that as light is only polarised by penetrating the surface, the forces which produce extraordinary refraction begin to act only at this limit. He also remarked, that the angle of incidence at which the spar polarises light by partial reflection is 56° 30'; and that whatever be the angle included between the plane of incidence and the principal section of the crystal, the ray reflected by the first surface is always polarised in the same manner. After stating these observations, Dr B. proceeded to observe, that his experiments upon the subject led him to draw different conclusions, and seemed to indicate that the polarising forces extend beyond the crystal. He also showed that the force of double refraction and polarisation originate

VOL. XII. PART II.

from the surface of bodies, though its intensity depends upon the inclination of the surface to the axis of the crystal; that the change in the angle of polarisation produced by the interior force, depends upon the inclination of the reflecting surface to the axis of the crystal, and upon the azimuthal angle which the plane of reflection forms with the principal section; and that the change in the direction of the polarisation depends upon the angle which the incident ray forms with the axis of the crystal.

March 11.-A paper by C. Bonnycastle, Esq. was read, entitled, "On the pressures which sustain a heavy body in equilibrium, when the points of support are more than three." The author observed, that there is no method, purely mathematical, by which the difficulties involved in this problem can be surmounted; but by considering the circumstances under which the pressure is usually generated, we may be enabled to discover the law of its distribution, and this law must always govern its proportional quantities and intensities. The paper concluded with an investigation of the case when the number of points of support is infinite, or, in other words, consists of a line or plane surface.

April 1.-A paper by Dr Brinkley was read, entitled, "Results of Observations made at Trinity College, Dublin, for determining the obliquity of the ecliptic, and the maximum of the aberration of light." After some general observations, the author proceeded to consider the opinion of astronomers, that observations of the winter solstice have given a less obliquity than those of the summer,-an opinion sanctioned by, the observations of Maskelyne, Arago, and Pond, but questioned by Bradley. Dr B. referred this diffe

N

rence to some unknown modification of refraction, and stated that he has observed, at the winter solstice, that the irregularity of refraction from the sun is greater than from the stars at the same zenith distance; whence he inferred the necessity of paying greater attention to the observations made at the winter solstice. The author next stated, from his own observations, the maximum aberration of light for last year to be 20.80". Another paper was likewise read, on some New Methods of investigating the sums of several classes of Infinite Series, by C. Babbage, Esq. From the nature of the subject, this paper did not admit of being read in detail; but the object of the author appears to have been to explain two methods of finding the sums of a variety of infinite series. The author stated, that results nearly similar to his own had been obtained by MM. Poisson and Lagrange, but neither of these mathematicians had explained the causes of the errors to which their method was liable, or given a method of correcting them.

April 22.-A paper by Captain J. Anderson, R. N. was read, entitled, "Some Observations on the Peculiarity of the Tides between Fairleigh and the North Foreland, with an explanation of the supposed meeting of the tides near Dungeness." After some general remarks on the common opinion, respecting the meeting of the tides between Dungeness Point and Rye Harbour, Captain A. proceeded to describe the peculiarity of the channel at that point, and its very sudden contraction between Dungeness and Cape d'Alprée, and between the South Foreland and Calais Point: In consequence of this contraction, the western tide, according to Captain A., meets with a resistance in its course at Dungeness and Cape d'Al

prée, from which the water must continue to accumulate until it deepens and widens the channel, so as to become adequate to its discharge. To this accumulation the author chiefly referred the peculiarities in the rise and fall of the tides in the neighbour. hood of the above-mentioned places. The formation of the coast, by gradually altering the course of the tides between the South Foreland and the Buoy of the Nore, from E. N. E. to W. N. W., occasions a gentle blend. ing of the waters, so that there is a strong eddy about the Kentish Knock, and a foaming ripple where they meet and proceed together.

At this meeting a paper was also read, by Sir E. Home, on the Ova of the opossum tribe.

A paper, entitled, "A case of a Blue Child, with the Dissection," was read, by J. F. Wood, Esq. This child lived twenty-one months. On removing the pericardium after death, a large vein was observed descending on the left side of the thorax, and terminating in the right auricle of the heart, in which the superior vena cava was also terminated by a distinct opening. The auricle was large, and the foramen ovale pervious. aorta and pulmonary artery arose from the right ventricle, the cavity of which was likewise large and strong, and had no communication with the left except by a foramen through the septum which divides the ventricles.

The

At this meeting a paper was likewise read by W. Morgan, Esq., entitled, "Observations on the New System of Diagonal Framing, introduced into H. M. Navy by R. Seppings, Esq." (now Sir Robert Seppings.) The author approved highly of the principles of this celebrated naval architect, and pointed out the great advantages arising from their adoption in practice.

April 29.-A paper was commenced by Dr Brewster, on the optical and physical properties of Tabasheer.

May 6.-Dr B's. paper was concluded. The Doctor entered at great length into the various properties of this substance, and detailed Mr Meron's experiments with the view of determining the power of tabasheer to absorb different fluids, and of ascertaining the corresponding effects produced upon its optical properties, specific gravity, &c.

May 18.-A paper by T. A. Knight, Esq. was read, on the different qualities of trees felled in spring and winter. From his experiments and observations, the author concluded, that in order to give durability to the alburnum of oak, the tree should be barked in spring, and felled in the ensuing winter.

May 20. At this and the previous meeting a paper by Dr Marcet was read, "On the Specific Gravity and Temperature of Sea Waters in different parts of the Ocean and in particular Seas; with some account of their Saline Contents." The object of this paper was to determine the general properties of sea waters in different parts of the ocean and at different depths, with the view of ascertaining whether they differed from one another, and in what respects. After some preliminary remarks, Dr M. proceeded to describe the instruments which had been contrived to raise water from different depths, or from the bottom of the seas when practicable, and which had been employed in collecting the different specimens. The three great points kept in view in the course of the examination were their specific gravity, their chemical composition, and their temperature, when this could be ascertained; and the author gave a circumstantial detail of the precautions attended to in the investigation of

these important points. The results" of the author's numerous observations and experiments were arranged in the form of tables, and consequent ly do not admit of being detailed. The general conclusion from the whole was, that the composition of sea waters in all parts of the ocean is very nearly the same, both in respect to the nature of the saline matters, and their relative proportions to one another; and that they only differ from one another, with respect to the absolute quantities of salt they contain. In the course of the paper, the following interesting facts were mentioned. Dr M. had been furnished with specimens of sea water from both the late Arctic Expeditions; and on comparing the labels attached to them, he found that in the Greenland seas, the temperature, as ascertained by Lieutenants Franklin and Beechy, uniformly increased with the depth; while in Baffin's Bay, according to the observations of Captain Ross and Lieutenant Parry, it was constantly diminished. Dr M. also found that specimens taken from the surface were generally not less saline than those taken from great depths, unless the surface had been lately thawed, when the quantity of saline matter was found to be much diminished. In speaking of the composition of sea waters, Dr M. stated the important discovery of Dr Wollaston, that they uniformly contained potash. The proportion of this alkali present Dr W. estimates at somewhat less than the th part of water at its common density; and he supposes it exists in the state of sulphate.

June 10, 17, and 24.-These three meetings were occupied in hearing read a paper by Captain H. Kater, entitled, "An account of Experiments for determining the length of the Pendulum vibrating seconds at the principal stations of the Trigono

ROYAL INSTITUTE OF FRance.

In the public sittings of the 22d of March 1819, a notice was read by M. Biot, on the continuation of the labours undertaken to determine the figure of the earth, and upon the results of the experiments on the pen dulum, made in 1817, at the Shetland Islands, by himself and others.

At first, it was merely known that the earth was of a round figure, which was easily ascertained by the circular form which its shadow presents when projected on the moon's disc during an eclipse. Newton afterwards discovered, by his calculations, that it was not completely round, but somewhat flattened at the poles, and protuberant at the equa

tor.

The methods of observation, yet imperfect, have, after great difficulty, established this truth, which has been at last obtained by measuring degrees of the meridian under the most distant latitudes, namely, at the equator and near the poles. The flatness of the poles was thus put beyond doubt. The operations prosecuted for the last fifty years in France, England, Sweden, America, and India, have succeeded in determining nearly its precise quantity. The mea surement of the arc of the meridian comprehended between Dunkirk and Barcelona, and accomplished with infinite precision by MM. Mechain and Delambre, was the foundation upon which the new system of French measures was constructed. The desire of communicating greater precision to these results, caused this first are to be prolonged across Spain as far as the Balearic Isles* ; and it became a part of an immense triangle above the Mediterranean. In fine, the same

motive caused the French Government to seize with avidity the opportunity offered, two years ago, of seeing this operation, already so grand, extend itself towards the north to nearly equal extent, in uniting with a portion of the same meridian, which stretches from the southern coast of England as far as the Shetland Isles, to a higher latitude than St Petersburgh; a portion which the scientific men of England have been now twenty years occupied in measuring.

In order to terminate this immense arc, which comprehends almost the fourth part of the distance from the equator to the pole, there remained nothing, last year, but to construct some triangles between the Shetland Isles and Scotland, by the medium of the Orkneys, and to connect the operations of the English and the French at the point of junction, Dunkirk, by means of a system of combined ope rations, in which the instruments employed by the observers of the two nations should be made to co-ope

rate.

This last labour was executed in the preceding autumn. MM. Arago: and Biot went to receive, at Dunkirk, the English observers, MM. Mudge, Colby, and Gardner, who brought with them the grand astronomical sector constructed by Ramsden, which they had made use of in all their preceding operations: and the French, on their part, brought one of their repeating circles.

At Dunkirk this fine instrument was, by the desire of the observers, placed within the marine arsenal, The English brig the Investigator, which had conveyed it thither, was also to bring it by the docks to the place where it was to be employed,