The first Lecture of the present Session, at this institution, which is dedicated to objects of science and the arts, and generally for the promotion of useful knowledge, was delivered on the evening of Thursday last, by the Rev. Wm. Scoresby, F.R.S., and Member of the Institute of France, on Magnetism; and notwithstanding the evening was most unfavourable, the theatre was completely filled, as also that the auditory were composed of professional gentlemen, and the most respectable families of this city and suburbs.
The Rev. Lecturer commenced about 20 minutes before 8 o’clock, introducing his subject by some extended observations on the general laws and agencies regulating and upholding the physical creation; illustrating his arguments by notices, showing great accuracy of observation, and an enlarged and comprehensive judgment! the conclusion that he drew being that all these are acting the part and performing the functions sssigned them, and in the sublime exhibitions we witness, furnish proofs of the eternal power and Godhead of the Great Creator. He then proceeded to speak of Magnetism, one of those mighty agencies,—subtile and yet potent, and with electricity, —with which it appears correspondent,—performing the grandest and most astonishing operations of nature. Their secret and concealed modes of action, which the most acute observers have not been able to penetrate, filled us with wonder, but at the same time,—probably also correspondent with the properties of light and heat,—afforded the most manifest proofs that they are essential to the conservation of the natural world.
The talented lecturer made honourable mention of Dr. Gilbert, an English philosopher of the sixteenth and seventeenth centuries, who, in the then infant state of the science, made many considerable experiments and discoveries, greatly enlarging the list of electrics, and of the bodies on which they act. He also spoke of the knowledge of these laws and agencies among the ancients, admitting that this must be understood in a very confined and limited sense. He, however, showed that they are alluded to by distinctive names in the most ancient records we possess, the books of the Old Testament, quoting the well known passages from the Psalms, and particularly the book of Job; to which the lecturer cannot but know, some critics have assigned a date even earlier than the time of Moses. Returning, however, to the proposed subject of his lecture, that of Magnetism, he did full justice to that singular people the Chinese, conceding to them a knowledge of the attractive power of the loadstone, long antecedent to its being known in the western part of the world. Their knowledge, however, of its property of communicating polarity to iron appears to have been of later date. Mr. Scoresby described their use of the loadstone in giving the point of direction to their chariots or carriages in their journeys; the definition given of it in their works being “a stone with which a direction can be given to the needle.” The same word (chin) being used by them to express the magnetic and the common working needle, as among ourselves. And in a subsequent part of the lecture, when treating of the compass, he admitted that while the knowledge of the directive power of the magnet was unknown to European nations generally till late in the twelfth, or about the middle of the thirteenth centuries, and even then did not appear to have been brought into common use for nautical purposes, it had been known and so used by the Chinese, and the people inhabiting that part of the world, from periods of high antiquity.
He also treated at length of the phenomenon of magnetism, observing that in certain bodies it seemed to be the result of the operation of its kindred agencies, as in the earth at large. In others an inherent quality, as exhibited in ferruginous bodies, or substances partaking of the particles and qualities of iron. This he also illustrated by a variety of experiments that appeared highly to interest, and could not fail to inform his auditors; using for these purposes several magnets of considerable power. In this too, he desired them to understand there was no mystery, nor any fluid circulating, because every particle of the steel was to be regarded as a magnet with two poles; and he showed that if a considerable number of magnetised needles were placed round the same magnet, they would be directed into curves. In treating of the laws and phenomena in permanent magnets, he showed that in magnetic bars it is strongest at the extremities, illustrating by experiment the proportion in different parts, and giving examples of the focus of attraction. The power at a distance received some neat illustration, as also the law of diminution; and in showing that it could not be intercepted, the lecturer was very happy. The effects of attraction in iron was exhibited in some very pleasing experiments; but his discourse on mutual attractive influences as illustrative of some planetary phenomena, had much of grandeur in it, and great sublimity of thought. He here treated of the principle of mutual attraction between all particles of matter throughout the universe, and the law of gravitation, or that force which effects the great motion in the orbit, and the smaller motions round its axis. These produce re-actions in the parts proportioned to their density; the actions and re-actions being directed to the centre of motion. Gravity then may be defined to be weight, proportional to the quantity of matter; density being measured by the quantity of matter and the magnitude. The law of gravitation being inversely as the square of the distance, and directly proportional to the mass or quantity of matter. Gravity, therefore, is a local result to each planet, and effects only its own parts, as patients of the common motions; and this the lecturer familiarly illustrated by calling the attention of his audience to a pound weight as settled and defined on this earth, and explaining to them what the ponderosity of the same relative proportion would be in the sun, and the contrary in the planet Saturn, whose comparative lightness approaches that of cork.
This he also carried further, by explaining that even on the earth we inhabit, the same bodies have not always the same weight, it being a well ascertained fact, that the weight of a body under the equator is less than at the poles. To prevent, however, misconception on this head, he desired his audience to bear in mind, that this difference is not to be discovered by means of a balance, or the scales usually employed upon these occasions, the weight against which the body is opposed being subject to the same variation. The whole then is a sublime law of aggregation, by which, by the simple contrivance of a two-fold motion, planetary masses are held together:–either motion stopt, the masses would disperse. Thus, were a piece of stone he held to be deprived of this magnetic power or influence, it would crumble into dust. Among the various applications then of the truth of a system of bodies, connected by this sort of attractive influence, and revolving about their common centre of gravity, none was more remarkable than the determination of the actual densities, or specific gravities, of the matter of which the several planets are composed. This also had been assisted by the degree of precision that is now given to the investigations of the mutual perturbations of the stars; there not being now a single perturbation, which has not been traced up to its origin in the mutual gravitation of the parts of the great system of nature. Reasoning also on the principles by which the actual densities of matter is determined, the talented lecturer was led to conceive the use that might be made of the magnet in determining the densities or thickness of masses in mining processes, or in those of tunnelling for rail-roads, or otherwise, and which having followed up, he has arrived, at conclusions that will be of infinite service, and hand his name down among those bright ornaments of mankind, who by their discoveries have acquired for themselves a never-dying fame. We know not whether Mr. Scoresby has as yet communicated the result of his experiments to this end to the public, but trust, should this not be the case, that he will not delay to do so.
While speaking also of the discoveries of a son of science whose residence among us, does honour to our city, we would allude to his invention for the depositing of, or reception of chronometers at sea. In navigation and astronomical observation, time is an essential element, and the chronometer or balance-watch, the instrument that is depended on for the knowledge of its lapse. Hence the value of a means of recuding, if not preventing the risk of error, and in this respect also Mr. Scoresby, by his ingenious discovery, which he exhibited to the audience, is a benefactor to mankind.
Mr. Scoresby also treated of the nature of the quality of polarity in magnets; of their directive property as before hinted at; of the deviation in the compass, &c., &c.; delighting his applauding audience, with whom time passed unheeded, until the lecturer himself discovered that it approached 10 o’clock, having spoken without interruption for hours; and concluding by expressing his intention of resuming the subject to-morrow, (Thursday) evening, at half-past 7 o’clock.
For ourselves, we would observe, that gratified as we were, our notice of this exceedingly interesting and well delivered lecture, is, (from confinement with respect to space,) necessarily very brief. If, however, it leads persons disposed to inquiry, and desirous of improving their stock of knowledge, to attend the continuing lectures, we shall not think our labour has not been in vain.
With respect to the lecturer himself we would say, it showed him to be a man of singular ability, and most indefatigable industry, Exact and ingenious, he directed the attention of his auditory to many branches of the science of which he treated; and showed that he had prosecuted considerable improvements.—Exeter Paper.