In 1852, the establishment commenced operations with a personnel consisting of four officials, two messengers, and fifteen laborers. At present nine hundred persons are employed. On August 1, 1852, the manufacture of postage stamps, stamped envelopes, newspaper wrappers, which until then had been made by private contract, was given to the bureau together with all the necessary machines and implements for the manufacture of the same, which had been the property of the Post-Office Department. At the close of the year 1860, when the Royal Lithographing Institute became combined with the Bureau of Engraving and Printing, it was found necessary to employ copper engraving with photographic and galvanoplastic processes in engraving of charts instead of lithography, and this change again was productive of an enlargement of the office together with a corresponding increase in machinery. A great source of revenue and profit was offered in the enormous supply of postage stamps and cards required by the totally unexpected development of the postal service. This kind of work had formerly been performed by the printing office of Decker, which by decree of May 23, 1877, had been purchased by the German Government for the sum of 6,780,000 mark ($1,695,000) and had been placed under the jurisdiction of the Postmaster-General. By law of May 15, 1879, the Prussian Bureau of Engraving was purchased by the Imperial Government for a consideration of 3,573,000 mark ($893,250) and consolidated with the printing establishment under the name, "Royal Bureau of Engraving and Printing." The amalgamation took place at once from a business point of view, the general supervision remaining in the hands of the chief of the German post and telegraph administration, in whose bureau a separate division was established under the name "Director of the Royal Bureau of Engraving and Printing." In order to accommodate the increased force of the combined offices, the adjacent buildings were purchased in May, 1879, for the sum of 517,500 mark ($129,375); the tearing down of the old buildings began at once and in the autumn of 1881 the new building was ready for occupation. The bureau at present employs ninety-five artists and regular mechanics, and seven hundred and seventy laborers (male and female), apprentices, and porters. The work of the bureau increases from year to year although a great deal of it, not involving money or bonds, is now turned over to private industries. At present the ordinary work required by the Government and bureaus represents about 120,000,000 sheets, of which the Imperial Post and Telegraph Administration uses about 13,000,000 sheets and about 60,000,000 cards, independent of the large amount of work ordered from private firms. HERTZ'S RESEARCHES ON ELECTRICAL OSCILLATIONS.* BY G. W. DE TUNZELMANN, B. SC. H. Hertz has been engaged for some time past in a series of researches on electrical oscillations, which have led to results of very exceptional importance, and as these results throw considerable light on the nature of electrical action, it will be of interest to have a connected account of the investigations, to which I therefore propose to devote a short series of papers. In Hertz's first paper on the subject, viz, "On Very Rapid Electrical Oscillations" (Wiedemann's Annalen, 1887, vol. XXXI, page 421), he refers to a paper by Colley, "On Some New Methods for Observing Electrical Oscillations, with Applications" (ibid., vol. XXVI, page 432), who calls attention to the fact that Sir William Thompson in 1853, showed the possibility of producing electrical oscillations by the discharge of a charged conductor, and gives references to all the investigations in the same direction which were known to him.t * From The Electrician (published in London), Sept. 14 to Nov. 16, 1888, vol. xxi, pp. 587, 625, 663, 696, 725, 757, 788; vol. xxII, pp. 16, 41. + For the benefit of readers who may wish to pursue the subject further the list is reproduced below: [Joseph Henry was the first to experimentally demonstrate the oscillation of electrical discharges, in June, 1842. Proceedings American Philosoph. Soc., vol. II, pages 193-196. Also, "Scientific Writings of Joseph Henry," published by the Smithsonian Institution; vol. I, page 200.] Von Helmholtz, "Erhaltung der Kraft." Berlin, 1847: Translated and published in Tyndall's "Scientific Memoirs," London, 1853, vol. 1, page 143. Also, "Gesammelte Abhandlungen," vol. 1, page 531. Sir William Thomson, L. E. D. Phil. Mag. 1853, vol. v, page 400. Also, matical and Physical Papers," vol. 1, page 540. "Mathe Feddersen, Poggendorff's Annalen, 1858, vol. III, page 69; 1859, vol. сvi, page 497; 1861, vol. CXII, page 452; 1861, vol. CXIII, page 437; 1862, vol. cxv, page 336; 1862, vol. CXVI, page 132. Kirchhoff, "Gesammelte Abhandlungen," page 168, containing remarks on and corrections of some of Feddersen's results. Von Oettingen, Poggendorff's Annalen, 1862, vol. cxv, page 513; and Jubelband of same, 1874, page 269. Bernstein, Poggendorff's Annalen, 1871, vol. CXLII, pages 54-88. Mouton, Thèse, Paris, 1876. Journal des Physique, 1876, vol. VI, pages 5 and 46. H. Mis. 224-10 145 According to these investigations, the electrical oscillations produced in an open circuit by means of an induction coil are measured by ten thousandths of a second, while in the case of the oscillatory discharge of a Leyden jar they are about a hundred times as rapid, as was shown by Feddersen. According to theory, still more rapid oscillations should be possible in an open circuit of wire of good conducting material, provided its ends are not connected with conductors of any considerable capacity; but it is not possible to determine from theory whether measurable oscillations are actually produced. Some observations of Hertz's led him to believe that under certain circumstances oscillations of this kind were produced, and his researches show that this is so, and that the oscillations are about a hundred times as rapid as those observed by Feddersen; so that their periods are measured by hundred millionths of a second, and they therefore occupy a position intermediate between acoustic and luminous vibrations. Preliminary Experiments.-It is known that if in the secondary circuit of an induction coil there be inserted, in addition to the ordinary air space, across which sparks pass, a Riess spark micrometer, with its poles joined by a long wire, the discharge will pass across the air space of the micrometer in preference to following the path of least resistance through the wire, provided this air space does not exceed a certain limit, and it is upon this principle that lightning protectors for telegraph lines are constructed. It might be expected that the sparks could he made to disappear by diminishing the length and resistance of the connecting wire; but Hertz finds that though the length of the sparks can be diminished in this way, it is almost impossible to get rid of them entirely, and they can still be observed when the balls of the micrometer are connected by a thick copper wire only a few centimeters in length. This shows that there must be variations in the potential measureable in hundredths of a volt in a portion of the circuit only a few centimeters in length, and it also gives an indirect proof of the enormous rapidity of the discharge, for the difference of potential between the micrometer knobs can only be due to self-induction in the connecting wire. Now the time occupied by variations in the potential of one of the knobs must be of the same order as that in which these variations can be transmitted through a short length of a good conductor to the second knob. The resistance of the wire connecting the knobs is found to be without sensible effect on the results. L. Lorenz, Wiedemann's Annalen, 1879, vol. VII, page 161. Olearsky, Verhandlungen der Academie von Krakau, 1882, vol. VII, page 141. Kolacek, Beiblätter zu Wiedemann's Annalen, 1883, vol. VII, page 541 (abstract of a paper published in the reports of the Bohemian Scientific Society in 1882). Bichat et Blondlot, Comptes Rendus, 1882, vol. XCIV, page 1590. Oberbeck, Wiedemann's Annalen, 1882, vol. XVII, pages 816 and 1040; 1883, vol. XIX, pages 213 and 265, In Fig. 1, A is an induction coil and B a discharge. The wire connecting the knobs 1 and 2 of the spark micrometer M, consists of a rectangle, half a meter in length, of copper wire 2 millimeters in diameter. This rectangle is connected with the secondary circuit of the coil in the manner shown in the diagram; and when the coil is in action, sparks-sometimes several millimeters in length-are seen to pass between the knobs 1 and 2, showing that there are violent electrical oscillations, not only in the secondary circuit. itself, but in any conductor in contact with it. This experiment shows even more clearly than the previ ous one that the rapidity of the oscillations is comparable with the velocity of transmission of electrical disturbances through the copper wire, which, according to all the evidence at our disposal, is nearly equal to the velocity of light. FIG. 1. In order to obtain micrometer sparks some millimeters in length, a powerful induction coil is required, and the one used by Hertz was 52 centimeters in length and 20 centimeters in diameter, provided with a mercury contact breaker, and excited by six large Bunsen cells. The discharger terminals consisted of brass knobs 3 centimeters in diameter. The experiments showed that the phenomenon depends to a very great extent on the nature of the sparks at the discharger, the micrometer sparks being found to be much weaker when the discharge in the secondary circuit took place between two points, or between a point and a plate, than when knobs were used. The micrometer sparks were also found to be greatly enfeebled when the secondary discharge took place in a rarified gas, and also when the sparks in the secondary were less than half a centimeter in length, while on the other hand, if they exceeded 1 centimeters the sparks could no longer be observed between the micrometer knobs. The length of secondary spark which was found to give the best results, and which was therefore employed in the further observations, was about three-quarters of a centimeter. Very slight differences in the nature of the secondary sparks were found to have great effect on those at the micrometer, and Hertz states that after some practice he was able to determine at once from the sound and appearance of the secondary spark whether it was of a kind to give the most powerful effects at the micrometer. The sparks which gave the best results were of a brilliant white color, only slightly jagged, and accompanied by a sharp crack. The influence of the spark is readily shown by increasing the distance between the discharger knobs beyond the striking distance, when the micrometer sparks disappear entirely, although the variations of potential are now greater than before. The length of the micrometer circuit has naturally an important influence on the length of the spark, as the greater its length the greater will be the retardation of the electrical wave in its passage through it from one knob of the micrometer to the other. The material, the resistance, and the diameter, of the wire of which the micrometer circuit is formed, have very little influence on the spark. The potential variations can not therefore be due to the resistance, and this was to be expected, for the rate of propagation of an electrical disturbance along a conductor depends mainly on its capacity and co-efficient of self-induction, and only to a very small extent on its resistance. The length of the wire connecting the micrometer circuit with the secondary circuit of the coil is also found to have very little influence, provided it does not exceed a few meters in length. The electrical disturbances must therefore traverse it without undergoing any appreciable change. The position of the point of the micrometer circuit which is joined to the secondary circuit, is on the other hand of the greatest importance, as would be expected, for if the point is placed symmetrically with respect to the two micrometer knobs the variations of potential will reach the latter in the same phase, and there will be no effect, as is verified by observation. If the two branches of the micrometer circuit on each side of the point of contact of the connection with the secondary are not symmetrical, the spark can not be made to disappear entirely; but a minimum effect is obtained when the point of contact is about half-way between the micrometer knobs. This point may be. called the null point. Fig. 2 shows the arrangement employed, e being the null point of the M 12 FIG. 2. A B rectangular circuit, which is 125 centimeters long by 80 centimeters broad. When the point of contact is at a or b, sparks of from 3 to 4 millimeters in length are observed, when it is at e no sparks are seen, but they can be made to re-appear by shifting the point of contact a few centimeters to the right or left of the null point. It should be noted that sparks only a few hundredths of a millimeter in length can be observed. If when the point of contact is at e another conductor is placed in contact with one of the micrometer knobs the sparks re-appear. Now the addition of this conductor can not produce any alteration in the time taken by the disturbances proceeding from e to reach the knobs, and therefore the phenomenon can not be due simply to single waves in the directions c a and d b respectively, but must be due to repeated reflection of the waves until a condition of stationary vibration is attained, and the addition of the conductor to one of the knobs must diminish or prevent the reflection of the waves from that terminal. It must be assumed then, that definite oscillations are set up in the micrometer cir |