This table is brown, long, wide, three feet high, judging by the eye. That is, it forms a little colored spot in the field of vision; in other words, produces a certain sensation on the optic nerve. It weighs ten pounds. That is, it produces a muscular sensation, less vigorous than would be produced by a weight of eleven pounds, more so than a weight of nine pounds would produce. It is hard and square, which simply mean that if pushed, or felt by the hand, it will excite other muscular sensations. Examine it closely as we will we find nothing else than the impressions which it makes upon us. We know nothing of bodies but the sensations they excite in us; know them simply as the unknown cause of our sensa tions. When we say that a body has existed in the absence of our sensations, we mean simply that, if in that time we had been in a certain position, we should have had sensations which we have not had. Hence philosophers like Berkeley have maintained, with a show of truth, that matter is a creature of the imagination, and that the whole universe of sense is reducible to an order of sensations.*

Thus our notion of external perception is a true hallucination. We only really know the sensation; simply that some feeling has become present to our consciousness which was not there before.† Our mind is constantly occupied in the reception of sensations, in the combination of the resulting images into ideas, and the recalling these images and ideas as apparent sensations, their illusionary character, only known from the simultaneous existence of real sensations, from their vagueness, and their intimate connection with a long train of less vivid images.

The mind has a general tendency to hallucination, through the predominance of the action of the brain-lobes over external action. But the vivid sensations constantly making their way in have a sharpness of outline seldom possessed by

* Taine's History of English Literature, vol. ii., p. 483.

All visible things are emblems; what thou seest is not there on its own account; strictly taken is not there at all. Matter exists only spiritually, and to represent some idea and body it forth.-Carlyle, Sartor Resartus, book i., ch. 11.

images, and thus rectify all our mental illusions. Even a distinct and vivid image thus becomes unreal when negatived by a real sensation, and generally only in dreams, when sensation is dormant, can our illusions gain the strength of reality. The act of sensation is thus analogous to that of recollection. The first is an excitation of the consciousness produced from without, the second the same action produced from within, perhaps in both cases through an action produced in the centres of the organs of sense; and the only positive difference is in the greater vagueness of the latter class of causes.

The act of sensation may be represented as a large bell rung in the sensory organs by a pull on the connecting nerves from the world without. This peal sets thousands of little bells ringing in the hemispheres of the brain. The ringing of these little bells decreases and we fail to hear them. If our attention be directed inward we again hear their peals, more "faint and far" than originally. If our attention be entirely withdrawn from externals, as in sleep, the action of the little bells may so increase as to set the large bell ringing, and so our images become virtual sensations.

The only difference between these and real sensation is in their lack of harmony with externals. Constantly troops of sensations are marching in upon our brain from without, all combined and in harmonious succession. If an image intrudes itself among these it is at once seen to be a stranger from another land, out of harmony with the actual sensations. Only when a well disciplined and organized troop of images take strong posession of the sensory centres, and overpower the real sensations present, is a waking hallucination possible.

Recollection is a stage of rectification. The image is really contemporary with the sensation, but it has a duration and extremities, and fails to exactly cover the present sensation. If it overlap it behind we have memory; if before, prevision. Images likewise overlap each other in the order of their reception, and we can thus place them in their proper relations in time. Images will sometimes impress us with a sense of present existence, but as they continue other images will thrust themselves between them and the present, pushing them fur

ther and further back, till their real relative position is attained. Their actual position in relation to the regular movement of time we have no real knowledge of. Our idea of it is but an arithmetical conclusion.

From the preceding considerations we perceive that our idea of the existence of matter means simply the existence of certain possibilities and necessities of sensation, influences from unknown causes affecting our nervous conditions, and referred, by long experience, to the extremities of the conducting nerves, or to exterior positions.* But we find it impossible to attain a practical belief in the hypothesis that these sensations have no physical cause, that they are solely mental in their origin and succession. We are forced to ascribe a positive material existence to exterior nature, an existence that radiates forces, which forces affect us mentally as sensations. Matter is thus, in all probability, a permanent possibility of sensation, existing independent of our senses, our idea of it resulting from a mental combination of the various forces with which it affects us into images possessed of geometrical and other relations.

These images form complete wholes, being the intimate combination of harmonizing forces. Were the characters of our sensory organs changed, complete wholes would still be formed, but essentially different in appearance. But as the whole universe would change in accordance the same harmony would continue. Thus our conception of the real character of what we designate matter is an illusion produced by the action of radiant forces on our mentality. But our simultaneous conception of the relations between these illusions is a correct image of nature, and yields us ideas of real relations existing between illusory sensations. We have then

* As our conception of a body is that of an unknown exciting cause of sensations, so our conception of a mind is that of an unknown recipient or percipient, of them: and not of them alone, but of all our other feelings. All which we are aware of, even in our minds, is a certain "thread of consciousness;" a series of feelings, that is, of sensations, thoughts, emotions, and volitions, more or less numerous and complicated.-Mill's System of Logic, vol. i, p? 68.

a relatively true, absolutely false, conception of nature, which has as many possible phases of appearance as there are possible modes of receiving sensations of force.

All changes occurring in our conceptions of objects are produced by loss or gain of possibilities of sensation, that is, by variation in the conditions of the forces affecting objects, or, more simply, by alteration of bodies. Beyond our senses, and in their absolute condition, bodies exist as distinct groups of motive forces and tendencies to motion; and it is only the widely entertained idea that motion cannot exist separately from substance moved, which inclines us to accept the primary evidence of our senses, and believe in the existence of a material substratum to the universe of forces.

All science consists in the investigation of the relations between our sensational ideas of the exterior world. All deduction is a mental chemistry in which these ideas are analyzed, and their elements combined into new forms, which may or may not conform to reality.

ART. II.-1. Philosophical Transactions of the Royal Society of London, vol. lxx, 1780, to vol. cviii, 1818.

2. Memoirs of the Royal Astronomical Society of London, for 1822.

3. Analyse de la Vie et des Travaux de Sir William Herschel, par M. ARAGO. Annuaire, 1842.

4. Histoire de l'Astronomie Moderne, par M. DELAMBRE. 2 vols. 4to.

1821.

In glancing over the history of science, we see some names that stand out, as it were, beyond others that have labored in the same fields; and such individuals, by their discoveries and improvements, have formed epochs in the progress of positive knowledge. It would seem, at first view, as if these had made immense strides in their efforts to unfold the mys

teries of Nature; and that scientific progress is not gradual, as up an inclined plane, but rather intermittent, like ascending by a flight of stairs. But many times this is more apparent than real. Discoveries are almost continually being made, and science is only in need occasionally of a mind of that peculiar nature which is required to put together the facts already known, and to show their connection and dependence, to deduce from them important consequences in relation to the development of knowledge. Such minds, however, generally possess transcendent ability for making discoveries-changing the unknown into the known. To this class belong Thales, Archimedes, Galileo, Kepler, Newton, and Laplace.

There are others, however, who by their improvements in instruments of research, and the invention of new ones, have added almost immeasurably to our knowledge of the nature of the physical universe. As belonging to this class, we may mention Aristarchus, Tycho Brahe, Galileo, William Gascoigne,* Sir William Herschel, and the inventors of the spectroscope. Herschel, by his improvements in the construction of large reflecting telescopes, and by his great skill in using them, wrought changes in our knowledge respecting the extent and physical constitution of the solar system and sidereal heavens, which have never been equalled, perhaps, since Galileo first turned his almost magic tube towards the bodies which occupy the celestial spaces.

William Herschel was, without doubt, one of the greatest astronomers of any age or country. For many years he has been the principal authority in astronomy for the general reader, and even for writers of school-books on astronomy; yet, less is known of his private history by the mass of readers, than of almost any other distinguished individual of modern times. He seems to have descended from obscure ancestors, and of his own individual history but little has come to us. Unless the man of science records his own trials and failures, his biographers find it very difficult or impossible

The inventor of the micrometer. See Grant's Hist. Phys. Astronomy,

p. 450.