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"It is not improbable that the electrical decomposition of the neutral salts in different cases may admit of economical uses. Well burned charcoal and plumbago, or charcoal and iron, might be made the exciting powers; and such an arrangement if erected upon an extensive scale, neutrosaline matter being employed in every series, would, there is every reason to believe, produce large quantities of acids and alkalies with very little trouble or expence.' pp. 51-54.
Altogether, the researches described in this paper furnish some of the most striking results, and suggest some of the most interesting topics of inquiry, that have flowed from chemical experiments, since the introduction of the new nomenclature. Indeed, the very ingenious and scientific Professor has already pursued his own course of argumentation and experiment with singular success; as we shall have occasion to describe more fully, in noticing his next communication to the Royal Society. At present, we have only to add, that a tribute of respect has been paid Mr. Davy on this occasion, by the author of a late splendid work, in which the apparatus employed in these experiments is placed as a new constellation, between Pegasus and the Eagle: and farther, that the Professor has been honoured with the prize, allotted by Bonaparte to the author of any discovery relating to Galvanism, which may constitute an important æra in the science.
II. On the Precession of Robertson, M. A. F. R. S. the University of Oxford. The phenomenon of the precession of the Equinoxes, which is one of the most important consequences of the theory of gravitation, and furnishes one of the strongest proofs of the truth of the Newtonian Philosophy, has exercised the powers of the greatest mathématicians and philosophers of the eighteenth century; yet has presented a difficulty, which till very lately has proved insuperable. To describe the general causes of this and other connected phenomena is sufficiently easy; but to go through the minutiae of the reasoning, and complete the computation, has been found difficult indeed. If the earth were exactly spherical, the particles of matter situated on different sides of its centre would be equally attracted by the sun, and there would not result any libratory motion about that centre. But the earth being formed protuberating toward the equatorial regions, in order to prevent the evils that would otherwise arise from the rotatory motion*, the equality of balance is destroyed. The particles composing the protuberance may be considered either as a kind of * See Ecl. Rev. Vol. iii. p. 1102.
By the Rev. Abram Savilian Professor of Geometry in Read Dec. 18, 1806.
meniscus embracing the globe, or as a congeries of little moons fixed in union one to another and to the terrestrial sphere. Now each of these would experience inequalities analogous to those of the real moon; that is to say, its nodes would retrograde with respect to the ecliptic, by the action of the sun. But these particles, adhering to the terrestrial globe, cannot have such a motion without first separating from it; they therefore tend to force it along with them in the retrogradation; and though their motion, communicated to so huge a mass, is considerably weakened, yet it is not entirely insensible. The entire mass, therefore, yields as it were little by little, and the equator of the earth retrogrades slowly over the ecliptic, thus producing the precession of the equinoxes. The moon acting upon the earth by its attraction in like manner with the sun, will of course occasion analogous motions; and the comparative minuteness of its mass is even more than compensated by its proximity. But as its positions with respect to the earth are incessantly changing, the effects which thence result are equally variable. Hence the action of the moon is not limited, as is that of the sun, to produce a motion in the equinoxes; it principally causes the obliquity of the ecliptic to vary, and produces the nutation of the earth's axis: and these inequalities, which are peculiarly due to it, have periods which depend upon its motions. The mean value of the precession being the result of the joint actions of the sun and moon, while the nutation is produced chiefly by that of the moon; these phenomena become interesting, not only on their own account, but because the ascertaining of their magnitudes furnishes a method of measuring the comparative magnitudes of the sun and moon. For these reasons, the determination of the precession has become a most important problem in physical astronomy. The method of solution was first sketched by Newton himself; and though, as his candid commentator Daniel Bernoulli remarks," he saw, through a veil, what others could hardly discover with a microscope in the light of the meridian sun," yet it was soon discovered that he had fallen into error in his investigations on this subject. Mr. Landen, in the first volume of his "Memoirs," has the honour of having first detected the source of Newton's mistake, by discovering that when a rigid annulus revolves with two motions, one in its own plane, and the other round one of its diameters, half the motive force acting upon the ring is counteracted by the centrifugal force arising from the compound motion, and half only is efficacious in accelerating the plane of the annulus round its diameter. Mr. L. however, did not expressly demonstrate this; but it has been done very elegantly by Dr. Brinkley, iņ
Dr. M. Young's valuable memoir on this intricate subject in vol. vii. of the Irish Transactions.
There still, however, remained something to accomplish; viz. to exhibit the solution of the problem in a form suited to the comprehension of those who were moderately versed in the geometrical and fluxional branches of science; and this is now attempted by Dr. Robertson, in a way that does him much credit. He considerably simplifies the process of investigation, by stating, on the most perspicuous and unexceptionable principles, the primary properties of compound rotatory motion. He then states the circumstances to which the earth is subject, as to the production of the precession of the equinoxes.
At the vernal equinox, for instance, a straight line drawn from the centre of the sun to that of the earth is in the plane of the equator, and therefore, as equal portions of the protuberant matter of the earth are above and below the ecliptic, the attractive power of the sun has no tendency to alter the position of the equator. But, in consequence of the earth's motion in its orbit, it very soon after the equinox presents a different position of the equator to the sun. The equilibrium of the protuberant parts of the earth, above and below the ecliptic, and towards the sun, is then done away, and the attraction of the sun on that side, where the greatest quantity of protuberant matter is, tends to bring down the equator into the ecliptic, or to cause the earth to revolve about a diameter of the equator. This attractive influence of the sun gradually increases a little till the summer solstice; it then gradually decreases in the same degree till the autumnal equinox, when it vanishes. From the autumnal equinox to the winter solstice it again gradually increases a little; and it then gradually decreases in the same degree till the vernal equinox, when it again vanishes. This recurrence and continuance of action is annually repeated.
Similar observations apply to the attraction of the moon on the protuberant parts of the earth. When a straight line drawn from her centre to that of the earth is in the plane of the equator, the attractive influence of the moon has no tendency to change the position of the equator, but in other situations, the attraction of the moon tends to bring the equator of the earth into the plane of the moon's orbit, or cause the earth to move round a diameter of the equator. The recurrences of the moon's action on the protuberant parts of the earth, and the times of their continuing, are repeated every month.
These effects of the sun and moon are to be considered separately; and for the reasons already stated, each of the actions, combined with the diarnal revolution of the earth, may be considered as a particular case of compound rotatory motion. It is needless, however, after investigating the effects of the sun's action, and expressing them in general formulæ, to go over the same steps for ascertaining those of the moon.' pp. 64, 65.
This passage is introductory to the only very difficult part in the inquiry, that is, the determination of the momentary alteration of the position of the earth's axis. The Doctor then combines the sun's disturbing force on the whole mass of the earth, the sun's centripetal force on the earth in its orbit, and the centripetal force of the earth on a body supposed to
revolve at the equator in the space of a diurnal revolution: and thus obtains an expression for the force causing precession. This is the greatest nicety in the whole solution; it required the most skill, and is treated with much perspicuity and comparative simplicity. The quantity of annual precession is then "calculated in the usual way, and also that of nutation, as far as they are produced by the disturbing force of the sun.' Dr. Robertson's results are 1" 27" for the nutation caused by the action of the sun in a quarter of a year, and 21". 0336 for the annual precession caused by the sun's disturbing force. These results agree nearly with those of Vince, and others, who have given the best solutions to the problem.
We have dwelt the longer upon this article, on account of its importance, and because it has been much misrepresented by some other critics. We would beg to suggest to the learned Professor, the propriety of completing the investigation, with a like regard to simplicity, taking the moon's action, and all the principal sources of irregularity, into the account; and publishing the whole in a separate work. The principal difficulty, is now surmounted; and the remaining labour will be greatly facilitated, by recollecting, with regard to difference of density, and variations of solidity and fluidity, the remarkable theorem of Laplace, that "Whatever be the law of the depth of the sea, and the figure of the spheroid which it surrounds, the phenomena of precession and nutation are the same as if the sea formed one solid mass with that spheroid."
III. An Account of two Children, born with Cataracts in their Eyes, to shew that their Sight was obscured in very different Degrees; with Experiments to determine the proportional Knowledge of Objects acquired by them immediately after the Cataracts were removed. By Everard Home, Esq. F. R. S. Read Jan. 15,
The two cases, here described, occurred under Mr. Home in St. George's Hospital, in the year 1806. Mr. H. has related them, because he thinks they serve to explain the reason of the difference between the celebrated observations of Mr. Cheselden, in the Phil. Trans. 1728, and those of Mr. Ware, in 1801. The conclusions drawn by Mr. Home, are as below:
That, where the eye before the cataract is removed, has only been capable of discerning light, without being able to distinguish colours, objects after its removal will seem to touch the eye, and there will be no knowledge of their outlines, which confirms the observations made by Mr. CHESELDEN:
That, where the eye has previously distinguished colours, there must also be an imperfect knowledge of distances, but not of outline, which however will afterwards be very soon acquired, as happened in Mr.
WARE's cases. This is proved by the history of the first boy in the present Paper, who before the operation had no knowledge of colours or distances, but after it, when his eye had only arrived at the same state, that the second boy's was in before the operation, he had learnt that the objects were at a distance, and of different colours: that when a child has acquired a new sense, nothing but great pain or absolute coercion, will prevent him from making use of it.
In a practical view, these cases confirm every thing, that has been stated by Mr. POTT and Mr. WARE, in proof of cataracts in chil-. dren being generally soft, and in favour of couching, as being the operation best adapted for removing them. They also lead us to a conclusion of no small importance, which has not before been adverted to; that, when the cataract has assumed a fluid form, the capsule, which is naturally a thin transparent membrane, has to resist the pressure of this fluid, which like every other diseased accumulation is liable to increase, and distend it, and therefore the capsule is rendered thicker and more opaque in its substance, like the coats of encysted tumours in general.
As such a change is liable to take place, the earlier the operation is performed in all children, who have cataracts completely formed, the greater is their chance of having distinct vision after the operation.' pp. 91, 92.
IV. Observations on the Structure of the different Cavities which constitute the Stomach of the Whale, compared with those of ruminating Animals, with a View to ascertain the Situation of the digestive Organ. By Everard Home, Esq. F. R. S. Read Feb. 12, 1807.
These observations are intended to shew, that the stomach of the whale forms a link in the gradation toward the stomachs of truly carnivorous animals. The whale examined by Mr. Home was thrown upon the Sussex coast, in August, 1806, and was brought to shore alive by the Worthing fisherIt had a stomach with four cavities, of which the first appeared peculiarly adapted to the solution of bones. Mr. Hunter, it seems, thought the second cavity to be the true digesting stomach; but Mr. Home concluded that in this animal, from the peculiarities of its economy, and the nature of the food, not only a cuticular stomach is necessary, but also two glandular ones, in which it undergoes changes preparatory to its being converted into chyle:" so that, in his opinion, chylification is completed in the fourth cavity. In our opinion, the examination of more subjects, in different circumstances, is necessary to determine the point. This paper is illustrated by two admirable engravings, by Basire. IV. On the Formation of the Bark of Trees. By T. A. Knight, Esq. F. R.S. Read Feb. 19, 1807.
Malpighi supposed that the cortical substance, which is annually generated, derives its origin from the older bark; the interior part of the new formed substance being annually transmuted into alburnum, or sap-wood: while the exterior part, becoming dry, forms the outward covering, or cortex. Hales,