so that the axis EQ being in the plane of the meridian and inclined to the horizon at an angle of 19° 30', the centre and plane of the plate were, during the revolution of the limb, always in the position I required. The distance between the centres of the needle and plate was, as before, 13.2 inches."

"Although the deviations due to rotation in these observations are in some cases greater than might perhaps on a first view be expected, if in the position in which I have supposed the plate, its rotation would really produce no deviation, yet the differences are not in any case more than may, I consider, be fairly attributed to errors in the adjustments. That the deviations, when the plate revolved from south to north, had a tendency most generally to be greater than when it revolved in a contrary direction, as is evident by referring to the Table, appears at first sight more unfavourable to my opinion than the magnitude of the difference; but on further consideration, I think that this will be allowed rather to point out the source of the errors in the results, than the incorrectness of my views, and that these errors arose from the plane of the plate not being in those cases perpendicular to the plane of the secondary to the equator and meridian. The proximity of the edge of the iron to the ends of the needle, varying from 5.16 inches to 4.27 inches at the south end, and from 5.16 inches to 5.92 inches at the north end, I considered to be another source of error; the inequalities arising from the effects of particular points near the edges of the iron on the ends of the needle being the more sensible when the distances are small. All my observations were made as near to the centre of the needle as the instrument would admit, in order that the effects of the rotation, since they were in many cases extremely small, might be the more sensible; and by this means I discovered the nature of the effects produced on the needle by the rotation of the plate; but I am fully convinced, that for the purpose of comparing the results of observation with the conclusions from theory, it is always desirable, that the observations should be made when the iron is at such a distance from the centre of the needle, that the effects of particular points near its edges, on the ends of the needle, are nearly insensible. Taking these circumstances into consideration, I was quite satisfied from these experiments, that, if the centre of the plate be in the secondary to the equator and meridian, and its plane perpendicular to the plane of that circle, the rotation of the plate will produce no effect on the absolute deviations caused by the

mass.

"In order to determine what effects would be produced by the rotation of the plate when its centre was in the secondary to the equator and meridian, and its plane in the plane of this circle, the instrument was adjusted as in fig. 1, the index at g pointing to 70° 30'; the limb SN was then placed at right angles to

SQN, and the arm A B attached to it with the iron plate on the axis; and that the centre of the needle might be in the plane of the plate, the compass box was moved in the direction of the meridian.

"Some of my first observations were made with the centre of the plate in the equator, and I immediately found, that the deviation due to rotation, instead of being 0, as in the cases when the plate revolved in the planes at right angles to its present position, was here considerable; and also that, that of the south end of the needle was in the direction of the upper, or south edge of the plate, contrary to what had been observed in the same plane at the pole. This indicated that there must be, at least, one point in this circle on each side of the pole, where the deviation due to rotation was 0; and to determine nearly the latitude of this point, I made observations at every 10° of latitude on each side of the south pole. Before, however, giving these observations, it is necessary that I should state the kind of reliance I place on them as forming a complete set. In order to make the observations near the pole, it was necessary to adjust the instrument with the axis horizontal and pointing east and west, and after having made the complete set, I suspected that in the change from the one adjustment to the other, the centre of the plate had been nearer to that of the needle in making the observations near the equator, than those near the pole; and that consequently, the deviations due to rotation in the former case, were proportionally too great. I was confirmed in this suspicion on comparing these observations with those which I had, in the first instance, made in lat. 0° and in lat. 90°; and still further on comparing them with others, which I subsequently made at the several distances 15, 17, 19, 20 inches; in the corresponding situations. For example, in my first observations, the deviations due to rotation in lat. 0°, long. 0°, and in lat. 0° long. 180° were 3° 10′, and 3° 14′, giving a mean 3° 12′ in lat. 0; and in lat. 90 S, 1° 31'; when the centres of the plate and needle had been carefully adjusted to the same distance 13-2 inches, in the two cases; whereas the corresponding deviations in the table are 3° 43′ and 1° 29'; and, by subsequent observations, I found the sum of the deviations at the distances 15, 17, 19, and 20 inches to be in these two cases, 7° 20′ and 3° 32', to which 3° 12′ and 1° 31′ are very nearly proportional. These differences however do not in the least affect the conclusions which I at the time drew from this set of observations."

"It appears, from these observations, that when the plate revolves in the plane of a secondary to the equator and meridian,

"1st. The deviation due to rotation is a maximum when the centre of the plate is in the equator.

"2d. It decreases as the plate approaches the pole, and is 0 between the latitudes 50° and 60°, apparently very nearly at 55°; and from this point it increases till it attains a maximum in a contrary direction at the pole.

"3d. At the south pole and on each side down to the latitude 55°, the deviation of the south end of the needle due to rotation is in the direction of the north or lower edge of the plate; or, from the south pole down to the latitude 55°, the south end of the needle moves towards the plate, when the inner edge of the plate moves from the south pole, and from the plate when the inner edge moves towards the south pole.

"4th. From the equator towards either pole as far nearly as the latitude 55°, the south end of the needle moves in the direction of the south edge of the plate; that is, it moves towards the plate when the inner edge of the plate moves towards the south pole, and from the plate, when that edge moves from the south pole; also the north end of the needle moves towards the plate, when the inner edge moves towards the north pole, and from the plate, when that edge moves from the north pole. Consequently towards whichever pole the inner edge moves, the corresponding end of the needle will move towards the plate from the equator to the latitude of 55° nearly, and the contrary will take place from the latitude 55° to the pole.

"The observations which I made with the plate on the north side of the equator, though not so multiplied as those on the south, were sufficient to show, that the deviations due to rotation observed the same laws on that side of the equator as I had noticed on the south side.

"The deviation due to the rotation of the plate, when its centre is in the secondary to the equator and meridian, having a peculiar character, namely, two greater maxima when the centre is in the equator, two less maxima, in a contrary direction, when the centre is in either pole, and four points where it vanishes, I consider to be particularly well adapted for forming an estimate of the correctness of any theory which may be adopted for the explanation of the phænomena in general; since the theory must be perfectly compatible with these peculiarities, before it can be applied to the explanation of the less marked phænomena.

"As it appeared from these observations, that the point where the deviation due to rotation vanishes, is not far from lat. 55°, the complement of which, 35°, is nearly half the angle of the dip, I wished to ascertain whether the deviation were really 0 in latitude 54° 45', which I considered to be correctly the complement of half the dip 70° 30′, although I could not see how the angle which the plane makes with the horizon could have an influence on an angle in the plane itself. Subsequent observations showed, that in this instance the deviation due to rotation vanishes, or nearly so, when the polar distance of the

centre of the plate is equal to half the angle which the dipping needle makes with the horizon. Whether this coincidence is purely accidental, or is a necessary consequence of the manner in which the effect is produced, must remain doubtful, until it can be shown how the action takes place; it, however, led me to ascertain precisely the point at which the deviation due to rotation vanishes,"

"General Law of the Deviation due to Rotation deduced from the Experiments.

Having now ascertained the nature of the effects produced on the horizontal needle by the rotation of the plate in different planes, I endeavoured to discover some general law, according to which the direction of the deviation depended on the direc tion of the rotation of the plate; so that the situation of the centre of the plate, the plane in which it revolved, and the direction of rotation being given, we might point out immediately the direction in which the deviation would take place.

"On comparing together all the facts which I have detailed, I found that this might be effected in the following manner. I refer the deviations of the horizontal needle to the deviations of magnetic particles in the direction of the dip, or to those of a dipping needle passing through its centre; so that, in whatever direction this imaginary dipping needle would deviate by the action of the iron, the horizontal needle would deviate in such a manner as to be in the same vertical plane with it: thus, when the north end of the horizontal needle deviates towards the west, and consequently the south end towards the east, I consider that it has obeyed the deviation of the axis of the imaginary dipping needle, whose northern extremity has deviated towards the west and its southern towards the east; so that the western side of the equator of this dipping needle has deviated towards the south pole of the sphere, and its eastern side towards the north pole. It would follow from this, that if the north and south sides of the equator of the dipping needle (referring to these points in the horizon) deviated towards the poles, no corresponding deviation would be observed in the horizontal needle; the effect, in this case, taking place in the meridian, would only be observable in the angle which the dipping needle made with the horizon. As it is not my intention at present to advance any hypothesis on the subject, I wish this to be considered only as a method of connecting all the phænomena under one general view. Assuming it then for this purpose, it will be found that the deviations of the horizontal needle due to rotation are always such as would be produced by the sides of the equator of this imaginary dipping needle deviating in directions contrary to the directions in which the edges of the plate move, that edge of the plate nearest to either edge of the equator producing the

greatest effect on it. By referring to the particular laws which I deduced at the time of making the experiments in different planes, it will be seen that they are all comprised under this general law; but this will be rendered more evident by taking an

instance.

"When the centre of the plate is in the meridian, and its plane a tangent to the sphere, the eastern side of the equator of the imaginary dipping needle, according to the above law, will deviate in a direction contrary to that of the motion of the eastern edge of the plate, and consequently the northern extremity of the axis will deviate in a contrary direction to that of the motion of the plate's northern edge, or it will deviate in the direction in which the southern edge of the plate moves. Hence the horizontal needle obeying the deviations of this dip ping needle, the deviations of its north end due to the rotation of the plate will be in the direction in which the south edge of the plate moves, which is the law deduced from the experiments first detailed." E. W. B.:

(To be continued.)

ARTICLE VIII."

Analysis of Acorns.

(To the Editors of the Annals of Philosophy.)

GENTLEMEN,

I BEG to inclose the notes made of some experiments to ascertain the component parts of the acorn. Although the analysis is not complete, and I have since found no leisure to supply what is wanting in it; yet it seems to contain some facts on the subject that I am not aware can elsewhere be found; and for that reason you may, perhaps, think the inclosed paper entitled to a place in your pages. Yours, &c. W. B..

[We could wish that the experiments of our correspondent had been more complete, as we are not fond of admitting fragments into the Annals of Philosophy. We publish his communication, however, in the hope that he will pursue the subject to a satisfactory conclusion.-Ed.]

Exper. 1.-350 grains of acorns were triturated in a marble mortar with water (about 24 pints), and passed through a fine hair sieve; what remained on the sieve, pressed and dried at a heat of about 130° for three hours, was a light-brown matter (B) weighing 63 grains.

(A.) What passed through the sieve deposited a white sedi