that it must have cost to produce a full and clear handling of so recondite a subject. The lecturer is probably right in his inference that the Gnostic idea of Christ's gathering His limbs together on the Cross is derived from the Egyptian myth of Osiris; and, in keeping with the Egyptian element in Gnosticism, I have seen at the British Museum a Gnostic gem consisting of Christ's haloed face carved on the back of a beetle. As the Egyptian beetle rolls together the ball of earth in which it has laid its egg, so, it was supposed, had a beetle once rolled together the ball of the sun; and hence Egyptian kings called themselves Sun-Beetles-Aa-khepru-Ra, Men-kheper-Ra, and the like: Christ was put on the same level by these dreamers. The CHAIRMAN, in closing the discussion, said that, while fully agreeing with the proposal to thank the lecturer very cordially for his research and labour, he doubted how far it was worth while to go so fully into what he might call the pathology of Christianity. Gnosticism was a system so wholly void of reason, method, and aim, that it defied real analysis, and led us only farther and farther into the mire and the dark. Was such a farrago of capricious and arbitrary notions really worth serious and prolonged study? The Cross was beyond all dispute the core and centre of vital Christianity. It was more than an emblem: it was a symbol of the last realities of the Gospel. The Gnostic vagaries about the Cross were merely idle and irrelevant fancies, without power or purpose. It was remarkable that St. Paul, the great exponent of the Cross, did not even mention the Cross or crucifixion in the greatest of all his epistles-that to the Romans. The resolution was cordially carried. WRITTEN COMMUNICATION. Rev. D. M. MCINTYRE, of Glasgow, wrote:— The Gnostic identification of the Cross with Christ may be due to the fact that from a very early period a cross (rectangular, usually, with equal arms), representing a star, was the symbol of Deity. According to Professor Sayce, the cross appears in Ancient Chaldea, on cylinders of the Kassite dynasty, evidently the ideogram for divinity And Sir Arthur Evans writes with reference to a small marble cross which he found in a central place in the shrine of the Cretan goddess-mother: "It must be borne in mind that the equal limbed Eastern cross retains the symbolic form of the primitive star sign, as we see it attached to the service of the Minoan divinities." This identification throws light on many passages of Scripture. Balaam, the prophet from Mesopotamia, for example, speaks of the Coming One: "There shall come forth a star out of Jacob, and a sceptre shall rise out of Israel." More than a thousand years later, wise men from the East came to worship the infant Christ, saying, "We have seen His star in the East." And in the Apocalypse our Lord, foretelling His return as King, testifies: "I am the bright, the morning star." Again, In Ezek. ix, 4, the "mark" spoken of is "tav," the last letter in the Hebrew alphabet, which, in the ancient script, was a cross. In the Apocalypse there is a cluster of texts, evidently based upon this vision of Ezekiel, which speak of the seal of the living God, which is itself the Name of God (vii, 3; ix, 4; xiv, 1; etc.) The Gnostic appellation of the Cross-" Horos," boundarymay recall the landmarks and waymarks which were put under the direct care of the Deity, and were, no doubt, often stamped with His name or symbol; just as the Celtic missionaries were accustomed to write, à, i (alpha and omega) on the menhirs and dolmens of paganism. 600TH ORDINARY GENERAL MEETING, HELD IN COMMITTEE ROOM B, THE CENTRAL HALL, SIR FRANK W. DYSON, F.R.S., The Astronomer Royal, The Minutes of the previous Meeting were read, confirmed and signed. The SECRETARY announced the death of the Rev. H. A. Crosbie, an Associate of the Institute. The CHAIRMAN then called on Dr. Sydney Chapman to read his paper Terrestrial Magnetism," which was illustrated by lantern slides. on "" TERRESTRIAL MAGNETISM. of o, By SYDNEY CHAPMAN, HE history of our subject for this afternoon began when men, long ages ago, discovered the power of attraction exercised towards iron by the mineral called lodestone. This property is mentioned in the writings of Thales (640-546 B.C.), so that it has been known for two thousand five hundred years or more. According to Lucretius (99-55 B.C.), the stone received the name of magnet from the place whence it was obtained, among the hills of Magnesia. From this the terms magnetism, magnetic force, and so on, are naturally derived. As the attractive property of the lodestone was gradually investigated, it appeared that small pieces of iron are specially attracted by two particular parts of the lodestone, which, in a stone of regular shape, are opposite to one another. These are called the poles of the magnet, and the stone is said to be magnetized in the direction of the line joining them. The next great discovery in magnetism related to the directive property of the lodestone. If a small magnet is mounted on a floating card or board, it is observed that the float and magnet will turn on the water till the magnetic axis, or line of poles, lies along a particular direction. Once the stone has assumed this direction, the tendency to motion ceases-there is no force on it tending to move it bodily. In early days the direction of the axis was supposed to be truly north and south, but it is now known that in most parts of the earth this is only approximately the case. This directive property of magnets was probably discovered independently among the Eastern and the Western nations, becoming known in Europe about the twelfth century of our era, and earlier still in China and Japan. This second discovery was of great practical importance and was soon turned to use in navigation. The magnet points sufficiently nearly to true north for it to be of great value to mariners, since it provided a means, which had hitherto been wanting, of indicating direction when out of sight of land cr— through cloudiness of sky-of the heavenly bodies. Thus the ship's compass was invented, the early forms consisting of a small needle-shaped magnet attached to a floating bowl or card, on which, later on, the points of the compass began to be marked. Many improvements in construction have been introduced in the course of centuries, and the use of iron in the structure of modern ships has necessitated the addition of special auxiliary devices to compensate for the disturbing effects on the compass. Fundamentally, however, the compass remains the same, and is still one of the most important aids to seamanship-and, it is becoming possible to say, of airmanship also. In time it was found that the peculiar properties of the natural magnet could be communicated, by rubbing, to pieces of iron, and that, if the iron was not too soft, the magnetization is retained for a considerable period. It thus became possible to prepare artificial magnets and compass needles. The first European treatise on the magnet seems to have been written in 1269 by Petrius Peregrinus, a Frenchman, and a disciple of Roger Bacon. He made precise experiments on the magnetic aura or sphere of influence surrounding a magnet, to which its properties were generally referred; in the language of modern science, this is termed "a field of magnetic force," but without any essential difference of meaning. Peregrinus thus clearly describes how the direction of force at the surface of a magnet can be mapped out and its poles determined: "The stone is to be made in globular form and polished in the same way as are crystals and other stones. Thus it is caused to conform in shape to the celestial sphere. Now place upon it a needle or elongated piece of iron, and draw a line in the direction of the needle, dividing the stone in two. Then put the needle in another place on the stone, and draw another line in the same way. This may be repeated with the needle in other positions. All of the lines thus drawn will run together in two points, just as all the meridian circles of the world run together in two opposite poles of the world." The direction of the magnetic force, however, is not to be supposed to lie along the surface of the magnet. Indeed, Peregrinus observed that a small needle stands perpendicularly to the surface of the stone at the poles, where the magnetic force also is strongest. A simple way of illustrating the distribution of magnetic force, not only on the surface but also in the space surrounding a magnet, is that of sprinkling iron filings over a sheet of paper or glass laid over or in the neighbourhood of the body. The little pieces of iron themselves become temporary magnets owing to the magnetic force surrounding the stone, and if the paper is lightly tapped they arrange themselves end to end so as to make the directions of the lines of magnetic force clearly apparent. By analogy with a spherical lodestone such as Peregrinus used, our illustrious countryman, William Gilbert, Physician to Queen Elizabeth, was led to the conclusion that the earth itself is a great magnet. In his famous treatise De Magnete (1600) he describes the earth as being a great round lodestone, the magnetic poles of which were supposed to be coincident with the poles of rotation. Some years earlier, in 1581, Robert Norman, an instrument maker of London, and formerly a seaman, had announced that, as in Peregrinus' lodestone, the magnetic force of the earth does not lie along its surface, i.e., it is not horizontal, but has also a vertical component. Ordinary compass needles are pivoted, and weighted so as to swing horizontally, but if perfectly balanced before magnetization, after they are magnetized they will exhibit a tendency to dip; in the northern hemisphere the north-seeking, and in the southern hemisphere the south-seeking end is the one which dips. The natural angle of the dip in London is in round figures 65° measured from the horizontal. This was discovered by Norman in 1576, and is a salient feature in the analogy between the earth and a spherical lodestone. Norman himself undoubtedly had some inkling of the idea which Gilbert afterwards clearly stated; he perceived that the dipping of the needle indicates that the point or source of force which the needle" respects" is in the earth and not in the heavens. |