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The photographic news
- Bandzählung
- 27.1883
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- Bandzählung
- No. 1308, September 28, 1883
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Band 27.1883
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- Titelblatt Titelblatt I
- Register Index III
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612 THE BRITISH ASSOCIATION AT SOUTHPORT. As is now ordinarily the case, the meeting had hut few features to considerably interest those who were not present; the holiday-making being certainly more to the fore than the strictly scientific work. The inhabitants of Southport entered heartily into the work of putting the town into festive trim, Lord Street being decorated with some taste, and the Pavilion was lighted with a very large number of Swan’s incandescent lamps. Mr. J. Glaisher presented the report on mathematical tables, and although much detailed work has been done, it is impossible at the present time to make any final recom mendations. One of the best attended lectures was that of Sir F. Bramwell, on the telephone, and the discourse was well illustrated by apparatus and experimental demonstrations. Sir F. Bramwell pointed out that the telephone was one of the newest instances of the application of science for the pur poses of man, as it was only six years ago that it was first ex plained at the Plymouth meeting of the Association by its inventor, Mr. Graham Bell, assisted by Mr. Preece, the elec trician to the Post Office. New, however, as the telephone was, it depended upon the application of well-known natural laws, the first of which was the generation and transmission of sound. Sir Frederick gave a variety of experiments to show how sound was produced by setting the air into vibration, and how it could be reproduced al a considerable distance by some mechanical con nection between the sounding body in vibration and another body capable of being put into vibration and of acting on the air in its neighbourhood. It might be expected that the vibrations of the air accompanying a sound would in their turn put a surface into vibration, and that this vibration, as it originated from a sound, should for the same surface always be the same for the same sound. But the logograph, or word writer, invented ten or twelve years ago by Mr. Barlow, past president of the civil engineers, although the principle was correct, failed in producing uniformity, and it was reserved for the American inventor, Mr. Edison, to produce an instrument capable of repeating intelligibly all the complex vibrations into which articulate speech could be put, reproducing at one end of a tube or rod a speech delivered at the other. But, obviously, the power of connection was limited to very short distances, while what was wanted in the telephone was sound at a distance not of feet or yards, but of miles. The difficulty had been got rid of by the employment of electricity, and the discovery by Faraday that if a coil of insulated wire were moved in the neighbourhood of a magnet, electricity would be induced in that wire ; that the circuit would be in one direction when the wire was moved towards one pole of the magnet, and in the opposite direction when moved away from that pole. It was to the practical application of this great dis covery of Faraday’s that we owed the whole of the industrial uses to which electricity was being now so largely applied, for by reason of it we were no longer compelled to generate elec tricity by the employment of batteries, but could obtain it by means of a steam-engine, of water-power, or by the use of a windmill, keeping in motion coils of wire in the neighbourhood of electro-magnets. It was on this cheap and powerful source of electricity that we depended for the electric light, for the deposition of metals in plating, and for the working of railways Another discourse of some interest was one by Professor McKendrick, on Galvani and animal electricity, and a very large assembly gathered together in the Pavilion to hear what the Professor had to say on the subject. After galvanic experiments came the notion that the nerves conveyed electricity from the brain and cord to the muscles, and, following the law that the new concepts of a man of science originate from ideas of familiar things, the muscle was forthwith compared to a Leyden jar, the inner surface of which became positive by nervous action, whilst the surface was negative. Motion was caused by the irritation of a kind of discharge, the positive, internal, surface being connected with the negative, external, surface. Volta doubted this, and held that the pheno mena observed by Galvani were due to very feeble currents of artificial electricity produced by the application of heterogeneous metals to the limbs of animals. In a critical inquiry made by Volta into this question, he was led to the invention of the Voltaic pile, which not only for a time threw into neglect the question [SEPTEMBER 28, 1888. of animal electricity, but also was the starting point of the elec trical science of the present day. Matteucci, of Pisa, investigated the matter, and found that currents could be obtained from animal structures, even where all suspicion of thermo-electric or chemical action was removed. He also discovered that the interior of muscles was negative to their surface, and that it was possible to make a kind of battery of the thighs of newly-killed frogs, which could produce chemical effects similar to those caused by Voltaic elements. Then came the labours of Du Bois Reymond, the present professor of physiology in the University of Berlin, which will always mark the com mencement of an epoch in the history of animal electricity. Recognizing that the detection of the feeble currents from animal structures depended on the delicacy and accuracy of the apparatus employed, he made many improvements in the construction of galvanometers, and in the arrangements for leading off the currents from living textures into the galvanometer. Such galvanometers must be exquisitely sensitive, and it is evident that just in pro portion as they are so, so will be the difficulty of making an arrangement which will lead off any current that may exist, say in living muscles, without causing a current itself. That is, the eletrodes of the galvanometer must be non-polarizable, even when touching muscle. Du Bois Reymond found that little troughs of zinc, filled with a saturated solution of sulphate of zinc, fulfilled these requirements. Into these are placed bits of blotting-paper, also wet with sulphate of zinc solution, and on the bits of blotting-paper are placed morsels of clay moistened with saliva. When the bits of clay are put into contact so as to make a circuit, no current passes through the galvanometer. If we now take a muscle from the back of the log of a frog, cut it across, and place it on the clay pads, so that the section of the muscle touches one pad, and the surface of the muscle the other, a current of electricity passes through the galvanometer, as shown by the swing of the needle. Similar currents may be obtained from nerve, although they are very much weaker. Much discussion has taken place as to what these currents really mean ; but the majority of physiologists agree with Hermann, of Zurich, in thinking that the current obtained on cutting or injuring the muscle or nerve, is really due to the dying of the muscle or nerve substance at the point of section, and that the so-called “ negative variation ” is the current indicating functional activity. That is, living substance dies at the plane of section, and in dying it acquires a lower potential than the living matter, thus giving rise to a current, Again, suppose a living muscle giving no current, on stimulating it, by irritating its nerve, so as to cause the muscle to contract, a lower potential is produced at the points in the muscle where the nerve fibres end, and there is thus a negatve variation. Further, it has been shown that this negative variation passes like a wave through the muscle substance, and that the wave has disappeared before the muscle contracts. If, then, electric changes occur during the activity of muscle and nerve, it is natural that physiologists might expect to detect changes in the beating heart. This is the case. It was shown by projecting its image on a screen, that the un injured frog’s heart, isolated from the body, still lives, and, whilst beating, gave with each beat an electrical-variation, as shown by the swing of the galvanometer needle. The uninjured heart gives no current, but when slightly injured there is a variation in its electrical state with each beat. Then the lecturer showed that light causes an electrical change in the eye. Placing the eye of a frog in the galvanometer cushions, it was shown that there was a current passing from the cornea to the back of the eye. In the dark, little or no change could be seen except what might be due to the drying of the living structures forming the eye ; on allowing light to fall on the eye, there was at once an increase in the current. This con tinued for a time, then began to fall off, and, on light being re moved, there was another increase, and then a sudden and rapid fall off. This action, first shown by Professor Holmgren, Pro fessor Dewar, and the lecturer, showed a specific influence of light on the retina. It could not be called a negative variation. It indicated chemical changes occurring in the retina. Lastly, the lecturer showed the production of currents from the living man. Placing the hands in two vulcanite troughs communicating by platinum plates with the galvanometer, and filled with a weak solution of salt, he showed that on contracting One arin, a deflec tion of the galvanometer needle was produced. When both aims were quiet there was no current, on contracting one arm a current was at once produced. This current the lecturer was inclined to think was due to action of the fluid on the skin, and not to currents from the muscles, and that the differences were due to differences of contact. In summing up, after a few remarks THE PHOTOGRAPHIC NEWS.
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