THE ALTERNATE CURRENT TRANSFORMER. BY EUGENE BETTS. Few questions in electrical engineering are at present discussed more than that of alternate current transmission. Its importance is seen from a practical standpoint in the rapid development of the alternate current system of incandescent lighting. It was practically not until the spring of 1887 that this system came into commercial operation in this country. In July, 1890, the Westinghouse Company had put in 301 central stations of a total generating capacity of 554,350 lamps of sixteen candle-power. This is an enormous growth, and, of course, does not by any means represent all the alternating plants in this country. It represents the investment of not far short of seventeen million dollars in these 301 central stations for lamps, wiring, dynamos and power plant. The importance of the system is due entirely to the ease with which the alternating current can be transformed from a lower voltage to a higher, or vice versa, thus admitting the use of a current of high potential for transmission over long distances, and its subsequent transformation into a current of low potential at the point of consumption. The essential part of the system is, therefore, the alternate current transformer, also called the converter. The transformer or converter consists essentially of an induction coil which can be used either way, that is, to "step up" or to "step down," to increase the E. M. F. or to decrease it. The generating current is called the primary current, and the coil it traverses the primary coil. The induced current is known as the secondary current, and the coil it traverses the secondary coil. The first transformer was constructed in 1831, by Faraday, who then discovered the extremely important principles of the remarkable action of a varying current upon an adjacent circuit. Following Faraday were a number of experimenters who contributed largely to the perfection of the induction coil, and hence the transformer. Prominent among these are Ruhmkorff, who brought the spark coil to a high state of perfection, and Varley, who, in 1856, described a form of induction coil having a laminated and closed magnetic circuit, closely resembling some of the modern forms of transformers. More practical transformers were later made by Fuller and De Meritens. In 1882, Garland & Gibbs patented a system of distributing by alternating currents, using a transformer of the Ruhmkorff type. In 1883, Kennedy used a modified Gramine ring as a transformer; and in 1885, Deri and Zipernowsky proposed the use of transformers for effecting the self-regulation of the alternate-current dynamo, and revived the use of transformers having laminated and closed magnetic circuits. In the same year, Ferrante brought out transformers constructed of iron strips. About this time Westinghouse obtained control in the United States of most of the English patents on transformers, and afterward developed the Westinghouse system. Improvements in details of construction have been made in England by Kapp, Snell, Mordey and Statter, and in the United States by Westinghouse, Brush, Slattery and the Thompson-Houston Co. An alternating current transformer may be regarded as a species of dynamo in which neither armature nor field magnet revolves, but in which the magnetism of the iron circuit is made to vary rapidly through periods of alternation by separately exciting it with an alternating current. The primary coil of the transformer corresponds to the fieldmagnet coil of the dynamo, the secondary of the transformer to the armature coil of the dynamo. Many of the rules of construction of dynamos, such as rules for insulation and lamination of cores, apply also to construction of transformers. Transformers are used in either of two ways: 1. In parallel, on constant potential systems; 2. In series, on constant current systems. In the first case the primary coils consist of many turns of fine wire, while in the second the primary coils consist of fewer turns of thicker wire. The general principles involved in the construction of transformers of either system are, however, the same. When a transformer is at work we have the following phenomena: 1. A wave of impressed primary electromotive force; 2. A wave of counter-electromotive force in the primary coil, but not coinciding in phase with the impressed; 3. A wave of primary current not coincid ing with either of the former; 4. A wave of magnetization lagging behind the primary-current wave by about a quarter period; 5. A wave of electromotive force in the secondary coil lagging behind the magnetization wave by a quarter period; 6. A wave of secondary current coinciding with the former in period if the external circuit contain no self-induction. The problem in designing transformers is to find what relations exist between these different waves as regards their relative positions and magnitudes. In practice these waves are so near true sine waves that they can be considered as such. Of fundamental importance is the law that several sine waves always combine into sine waves again, are always induced by sine waves and induce sine waves. Therefore, if the primary electromotive force of a transformer follows the sine law all the electromotive forces, currents and magnetomotive forces must follow the sine law also. The losses of energy in the working of transformers must therefore follow very nearly the form of the sine wave, and thus their relation to the currents transmitted can be readily obtained. The principal losses of energy occur through hysteresis, eddy-currents and resistance of coils. Hysteresis is the lagging of the change of magnetization behind the primary current; it is due to the inertia or friction of the iron particles against rapidly changing their magnetization. The loss of energy due to hysteresis is directly proportional to the number of periods and very nearly proportional to the one-sixth power of the magnetization. This energy is dissipated in the form of heat, and the loss can be reduced by lowering the frequency of alternation and reducing the intensity of magnetization by increasing the cross-section of the core. Eddy currents are Foucault currents in the core, causing its heating. They can be largely overcome by laminating the core. The loss of energy due to eddy currents in the iron has been found to be very nearly proportional to the square of the magnetization and proportional to the square of the number of periods. The question of frequency of alternation as regards transformers is of considerable practical importance, as a transformer working at a frequency of 100 need be worked at only half the induction of an equal transformer worked at a frequency of 50. But as losses due to hysteresis and Foucault currents increase rapidly with the increase of frequency the limit of economical working is soon reached. The average European practice is 8,750 reversals per minute, while the American practice is 16,000 reversals per minute. This great difference may to a large extent be accounted for by the general preference of European engineers for machines running at moderate speeds. However, with the present imperfect knowledge of this subject it is not possible to determine this limit on theoretical grounds. The efficiency of well-built transformers is remarkably high, averaging about 95 per cent. for full load, and sometimes nearly 99 per cent. is obtained. HISTORY OF THE FEEDING APPARATUS OF THE OYSTER. BY P. C. FIELD. I. List of figures. CONTENTS. II. Method of preparation. III. General relations and gross structure of gills. V. Physiology. I. LIST OF FIGURES. No. 1. Horizontal longitudinal section of gills........................ Magnification. 11 diameters. No. 2. Horizontal longitudinal section across our water-tube............. 200 No. 3. Horizontal longitudinal section across two gill ridges and an inter-lamella junction................................. 66 ............ 580 No. 4. Vertical longitudinal section of a gill-lamella, showing water pores....... 130 66 No. 7. Cross-section of palp-ridges............ No. 5. Vertical longitudinal section through two gill ridges.............. 580 No. 8. Cross-section of the stomach and intestines... II. METHOD OF PREPARATION. Pieces were cut from fresh oysters, and some of these were put into corrosive sublimate for 12 hours, then washed for the same length of time in water. Other pieces were put into picric acid for 12 hours, while still others, untreated, were then placed, together with the corrosive sublimate and picric acid specimens, into weak and strong alcohol successively. After total dehydration, the specimens were put into turpentine |