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It has been remarked for some time since cially light, it might be best explained by that Pulkova and Berlin change from year a change in the position of the earth's to year their geographical position. Their axis; but such a change was also consid. latitudes decrease; every year the two ered until now as highly improbable. observatories seem to move away from the Schiaparelli, the great Italian astronoNorth Pole by a few inches; and as they mer, fully grasped these weighty considdo not move in reality, there is no alterna- erations, and they induced him to revise, tive but to conclude (after having tried all a few years ago, the whole question as to possible explanations) that the North Pole the supposed invariability of the axis of itself changes its position, although such rotation of the earth. He calculated the a movement had been hitherto considered effects which slight displacements of matas most improbable by all scientists. ter on the earth's surface might have upon
We all know were it only from ob- the position of the axis, and he demonservations upon a spinning-top— that if a strated by mathematical analysis that solid body is rotating, its axis may change slight bui prolonged geological changes its position in space, but that relatively to "may give origin to great displacements the rotating body itself it remains un. of the poles of rotation, provided the changed. A spinning-top may incline earth's spheroid is not of absolute rigid. towards the door, and its axis of rotation ity." may describe a conical surface, but it does The same position was taken by George not alter its position within the top; each C. Comstock,t who examined the available of the particles of the top describes the and sufficiently reliable determinations of same circle round the same spot of the latitudes at several observatories, and conaxis. The same was considered to be cluded that they give some support to the true as regards the earth. Its axis of rohypothesis of a secular shifting of the tation slowly changes its position in space; axis of the earth. Thus, the latitude of but within the earth itself, we were told, it Greenwich has pretty regularly decreased remaios unaltered. So that if two Arctic from 51° 28' 38":59 in 1826 to 51° 28' travellers attained the North and the South 37''95 in 1889. The Pulkova observations Poles, and erected two cairns upon these (especially reliable for this subject) show spots, the cairns would always represent a decrease of latitude of o”:33 during the the position of the axis of rotation of the years 1843 to 1882, which (taking into acearth. And yet recent observations tend count the probable errors) corresponds to to overthrow this view; we learn that the shifting of nearly six inches every year cairas must continually be shifted in order (o”:005). Another quite independent Pulto represent the true position of the Poles. kova series gives much the same result.
The importance of this discovery for Königsberg moves away from the Pole the physical geographer is self-evident. by 0"003 every year, while Washburn, The geologist has no means to explain by in Wisconsin, approaches the Pole by terrestrial causes alone two great geolog. 0"043 in the twelve months. The four ical facts of primary importance; the would well agree together if the Pole glaciation of the earth, and the extension, were shifting every year by over four feet during the Tertiary epoch, of a very rich (o”:044) along the meridian of 69° west of flowering and fruit-bearing vegetation, now Greenwich. Several other observations characteristic of southern Europe, over a (Cambridge, Prague, Potsdam) also speak wide continent which embraced Greenlaod, in favor of a shifting of the Pole. Spitzbergen, the Arctic islands of Siberia, The whole question is so important that and North America. If the simultaneous the Geodetical Association decided, at the glaciations of both hemispheres be provedend of 1890, to send an astronomical ex— and some specialists are of this opin- pedition to Honolulu (189° east of Berlin), ion, while those who oppose it will confess in order to make there consecutive deterthat the whole question has not been stud- minations of latitudes which might be ied sufficiently – it could not be explained compared with those of Pulkova and Berby astronomical hypotheses implying the lin. The expedition began its observaalternate glaciation of the two hemi- tions in June last, and the measurements spheres. Nothing short of a decrease in of the first three months, now fully comthe amount of heat received from the sun puted, prove that the changes were enwould give the explanation ; but few as. tronomers would be prepared to make such • Annales of the Pulkova Observatory, 50th anni. an admission. As to the prevalence of a versary volume, St. Petersburg, 1889; Italian text in rich flora in Arctic regions which receive # Pisa, October, 1891, fasc. 7 and 8; American but a limited amount of heat, and espe. Fournal of Science, December, 1891.
Il Nuova Cimento,
tirely accordant in magnitude with the light or radiant heat is transmitted through European ones, but, as foreseen, they the interstellar space, or through the were in the opposite direction. However, vacuum obtained in a glass tube — that is, a new explanation has been proposed in through space in which we detect almost the mean time by S. S. Chandler,* namely, no traces of ponderous matter (matter that the variation is merely periodical, and acted upon by gravitation) - we explain will be completed in fourteen months. the transmission of the luminous and heat Fourteen months hence the axis will re- energy by making a plausible supposition ; turn to its present position. But this we assume that besides the matter which explanation does not account for the constitutes the solid, liquid, and gaseous above-mentioned secular variations, so bodies, there is some other matter, or that we must wait now for further observa- rather some other still more attenuated tions. One thing is, however, certain : condition of matter, inseparable from the the axis of the earth is not so immutable former, which we call eiher; and we as. as it was supposed to be, and it is possible sume that the displacements of the partithat the study now being pursued by Mr. cles of ether (vibrations, or, maybe, other Lockyer of old Egyptian monuments, changes of state) are the medium for the which used to be astronomical observa transmission of luminous and heat energy. tories as well, may give some indications It was quite natural, therefore, to suppose as to the changes of latitude since that - and it was supposed — that the transremote period.
mission of electro-magnetic disturbances
is effected in the same way; that they also III.
produce vibrations, or some other changes The interest awakened some three in the usual conditions of the particles of years ago by the novel and startling exper- the surrounding ether; and that these iments in electricity made by the Karls. changes, or vibrations, are transmitted in ruhe Professor Hertz is still maintained. all directions from one particle of ether to They not only confirmed the long since the next, at some measurable speed – the suspected connection between electricity, speed of transmission probably being not magnetism, light, and radiant heat; they much different from the speed of transalso gave a new impulse to speculations as mission of light and radiant heat, which to the structure of matter altogether, and is about one hundred and eighty thousand the modes of transmission of energy. miles in a second. Numerous works on these subjects, all However probable this hypothesis, physmore or less connected with the Karlsruhe icists had hitherto failed to confirm it. researches, are continually appearing, and Maxwell advocated it chiefly on theoretin order to appreciate them we are bound ical grounds, but decisive experiments to revert to the starting point – Hertz's were wanted; and although Siemens had experiments themselves. The best means once measured the speed of transmission for mastering a new branch of science, it of electricity, and found it not very differ. has been remarked, is to study it in its ent from that of light,* his measurements nascent state.
were still considered as uncertain. Now When a moving body — say, a billiard came Hertz with his ingenious experiball — strikes another body at rest, and, ments. He applied a method which bad imparting to it part of its energy, sets it proved most successful in studying sound. in motion; when the waves, originated on When a tuning-fork is set vibrating, its the surface of a pond by a falling stone, vibrations alternately condense and rarefy spread in wider and wider circles, and the surrounding air, and both rarefactions finally begin to rock a piece of wood that and condensations are transmitted by the was quietly floating in a corner of the air in all directions; we may call them, pond; or when a tuning-fork communicates by analogy, waves. Now, if these waves its vibrations to another fork at a certain meet anywhere a reflecting board, they are distance - we may not be able to trace all sent back, in the same way as the waves the complicated movements of the two of the sea are reflected by the wall of a balls, the water of the pond, and the air; quay. But they may be sent back so that but our mind is satisfied to some extent each reflected condensation meets on its as to the manner of transmission of energy back journey with a new condensation from one ball to the other, from the stone coming from the fork, and in that case the to the piece of wood, and from the sound sound is reinforced; or, each reflected ing fork to the other fork. Again, when
* Two hundred thousand to two hundred and sixty Astronomical Journal, Nos. 248-251; American thousand kilomètres in a second; the velocity of light Journal of Science, February, 1892.
being about three hundred thousand kilomètres.
condensation meets with a rarefaction, and three instruments — the vibrator, the in this case both actions neutralize each screen, and the detector — the experiother — the sound is weakened. So that, ments could be carried on, and they if we slowly approach our reflecting board proved at once the close connection exto the fork, there will be places where the isting between the phenomena of elecboard reinforces the sound (condensations tricity and light. meeting with condensations), then weak- As soon as sparking began in the ens it, and then makes it louder again, vibrator, and the detector was approached although the board is moved all the time to it, sparks began to jerk between the in one direction, towards the tuning-fork. knobs of the latter ; but they disappeared
Of course, things are not so easy with as soon as the screen was interposed beelectricity. There is no great difficulty tween the two — the “waves " being interin producing alternate electrifications of rupted in this case. On the contrary, the surrounding ether which would corre- when the screen was placed immediately spond to the alternate condensations of behind the detector, strong sparking fol. the air, but they must follow each other lowed; if it was removed about eighteen with a tremendous rapidity. In fact, if feet, the sparking ceased; the direct and the tuning-fork makes, say, one thousand the reflected waves extinguishing each vibrations in the second the speed of other; but when the screen was moved sound in dry air being but eleven hundred away for another eighteen feet, sparking feet in the same time - a condensation reappeared — the two waves reinforcing will only have travelled a little over one each other, and so on. In short, the phefoot before a new condensation follows it. nomena were exactly like those which The "waves" of sound will be I'I foot would be noticed if' a tuning-fork, a relong. But if our electrical discharges flecting board, and a resonator were used. also succeeded each other with a fre- It was thus proved that each electrical quency of no more than one thousand dis- discharge produces some disturbance in charges in a second, the electric wave the surrounding space; that the disturb. (supposing that it spreads at the rate of ance is transmitted, through the “nonone hundred and eighty thousand miles in conductive ” air, exactly as luminous or a second, like light) would have travelled sound vibrations are transmitted ; and that one hundred and eighty miles before a electricity is propagated, like beat and new wave would be originated by the next light, at some finite and measurable speed. discharge. And waves of that length are of course it would not be possible to give not easy to deal with. So that, in order here the tedious processes by which the to obtain waves of a reasonable length measurements were made, nor to tell the following each other at a distance of, say, difficulties, the doubts, and the seemingly thirty-five or forty feet — Hertz had to contradictory facts which were met with produce discharges alternating thirty mil. in the way; although dating from yester. lion times in a second.* So he did. He day, “ Hertz's experiments " have already obtained such rapid discharges for very a whole history. Suffice it to say, that ihe short intervals of time, and thus he could
velocity of electricity, both in the air and measure the distances at which the elec- the conductive wires, proved to be very trical "waves " followed each other. A
near to that of light, namely, about one reflecting board, and some means for de hundred and eighty thousand miles in a tecting the “loops and nodes,” i.e., the
second. places where the waves reinforce or extinguish each other, were the next requisites. than one-tenth of an inch. When the plates were elec
A reflecting board was readily made trified by an induction coil, a series of sparks jerked out of a sheet of zinc, ten to twelve feet from one knob to the other, the charge rapidly passing
forwards and backwards, and giving very rapid alternaIsquare. As to the “detector," Hertz tive discharges. This was the vibrator." chose, out of the various means at his
detector,' “resonator," it consisted of a thick disposal, a brass wire, provided with two knobs, and the length of which was taken so as to suit
wire, the two ends of which were provided with brass knobs and bent into a ring, which could the oscillations in the vibrators. The wire being bent give sparks when it received electrical into a circle, its two knobs were brought very near to
each other, so as to show sparks at the reception of the waves of a certain length. With these feeblest electric waves (Sitzungsberichte der Berliner
Acad. der Wissenschaften, February 9, 1888). • Thirty million times thirty-five feet would make hardly needs adding that during the experiments the one hundred and eighty thousand miles.
As to the
reflecting board, or the apparatus used instead, re+ To attain a very rapid succession of alternate elec- mained stationary, and that the resonator was moved trifications, Hertz used two brass plates, twelve inches instead of it. square, to each of which was attached a thick wire, in the last chapter of Th. Preston's “ Theory of Light.' about two inches long, terminated by a brass knob. The London, 1890. The general reader may consult the distance between the two knobs was very small — less very good papers in Nature, March 5 and 14, 1890.
For more details see an excellent résumé
This may be considered as the first part | and, in fact, nearly all that is now written of the experiments. The second part is upon electricity is in some way connected even more interesting, as it disclosed fur- with them. First of all, it was necessary ther analogies between electro-magoetism to verify the experiments; and so they and light. Light is traosmitted by some were verified by several pbysicists - in bodies, and is reflected by other bodies. this country by Professor Fitzgerald and Electro-magnetic waves behave in the Fr. Trutton at Dublin, * and by Professor same way; a plate of zinc acts upon them Lodge and Mr. Dragoumis at Liverpool.t as a mirror and sends them back, but they In fact, Professor Lodge had nearly dispass through a wooden door just as light covered the same phenomena simultane. passes through a window plate. Hertzously with Hertz, as he was making in could send them into the next room 1887 and 1888 his experiments on the rapid through a shut door. If we put a red-hot discharges obtained from Leyden jars. iron ball in the focus of a parabolic mir. Blondlot, in France, slightly modifying ror, we may make it light a match adjusted the primitive experiments, finally settled in the focus of another parabolic mirror the velocity of electricity in the air at from which is placed at the other end of a room. two hurdred and ninety.one thousand to Electricity behaves in the same way; we three hundred and four thousand kilomè. can send beams of electrical oscillations tres in the second, thus very nearly by means of a parabolic mirror, and inter- approaching to the velocities of light. cept them at a distance by another mirror Then, Hertz himself having been brought aod send them into its focus. If we in by his earlier measurements to admit that terrupt the initial discharges in a certain the speed of the electrical disturbances is way - as they are interrupted in the much smaller in wires than in the sur. Morse alphabet - we shall transmit elec-rounding air, more careful measurements trical signals and have a telegraph without were required, and they were made in connecting wires. Light is refracted by Geneva and in Germany, and proved that transparent bodies if they have the shape the velocity, as foreseen by theory, is of a prism or a lens; and by means of a equal in both cases. || big prism of pitch Hertz refracted the Another important matter was to study electro-magnetic rays ;" he could bend the magnetic part of the same electric dis. them, and send them under a right angle turbances. In Maxwell's theory the maginto another room. Reflected light can be netic disturbances ought to be cothing polarized, and electro-magnetic "rays " but transversal rotations of the particles are polarized, too. In short, Maxwell's of ether in a plane perpendicular to the hypothesis as to the identity of light and line of transmission of light and electricity electricity is fully confirmed. Both are _"molecular vortices," as he used to disturbances (vibrations, or whatever they say. And Hertz succeeded in proving might be) in the usual state of ether which by a new series of experiments — or, at are transmitted like all other kinds of least, in rendering it most probable - that energy — like the energy of the billiard the magnetic force obeys in its transmis. ball, the stone, and the tuning-fork, of sion the same laws as electricity, but that which we spoke at the beginning of this the direction of its vibrations is perpenchapter, that is, from one particle to the dicular to the line of transmission of the next.
electric waves ; and he made at the same So we finally part with the mysterious time an attempt at measuring the mechan. "electric fuid ”just as we parted, thirty ical effects of the electric disturbances.** years ago, with the “caloric fluid," and we simply have before us a separate mode of • Nature, vol. xxxix., p. 391, vol. xli., p. 295. energy. When the waves of ether have † Ib. vol. xxxix., p. 548. lengths of from '000012 to '000016 parts Society (vol. 1., No. 302, August 28, 1891): “ This same
Prof. Lodge writes, in the Proceedings of the Royal of an inch, we have chemical energy; discovery (Hertz's) would have been made by the audiwhen they follow each other at distances ence at the Royal Institution on the evening of March
8, 1889, if it had not been made before; for, during a of from '000016 to 00003 parts of the lecture on Leyden jars, every time one was discharged inch, our eye sees them as light; when through a considerable lengıh of wire, the heavily gilt
paper sparkled brightly by reason of the incident they grew to '00012 parts of the inch, we radiation. see them no more, but we feel them as § Comptes Rendus, 1891, t. 112, P, 1058; t. 113, p. radiant heat; and when they attain lengths
|| Sarasin et L. de la Rive in Comptes Rendus, 1891, which are measured by yards and miles, t. 112, Nos. 12 et 13 ; Rubens and Ritter in Wiedethey give the electrical phenomena. mann's Annalen der Physik, 1890, vol. xl. Á wide series of researches was evi- Magnetism, second edition, 1881.
See $ 822 of Maxwell's Treatise on Electricity and dently called into life by these researches, ** "Ueber die mechanischen Wirkungen electrischer
At the same time a further confirmation mathematical and highly suggestive as of the light theory of electricity was given regards the very structure of matter,* and by Arons and Rubens, who proved that some others opening new fields for exper. the relation which, according to Maxwell, imental work, like J. J. Thomson's reought to exist between the isolating power searches into the speed of propagation of of various substances and their powers of the luminous discharge of electricity refracting the rays of light, exists in real through a rarefied gas, † and Hertz's new ity. The resistance offered to the passage experiments upon the transmission of the of light and that offered to the passage of same discharges through various screens, electricity are connected by a simple rela- transparent or not for light I-might be tion.* On the other side, Sir William mentioned in connection with the above. Thomson read before the Royal Society a But we must say, at least, a few words most interesting paper on the screens, about the quite new lines of research in. and their efficiency against waves of dif- dicated by Mr. Crookes's experiments on ferent lengths. He demonstrated that if what he names “electrical evaporation." the electric sparks have a frequency of It was already known that an induction four or five per second, a clean white current, when passing through the platpaper screen is sufficient to stop them; inum electrodes of a vacuum tube, tears but when the frequency of the sparks is off the molecules of platinum from the fifty, or more, the white paper screen sphere of attraction of the wire, and transmakes no perceptible difference. If the ports them to a certain distance. Now, paper is thoroughly blackened with ink on Mr. Crookes, comparing these phenomena both sides, some moderate frequency of a with those of evaporation of liquids, made few hundreds per second is, no doubt, various experiments in order to determine sufficient to practically annul the effect of the “evaporating" power of the electric the interposition of the screen. For dis- stress under different circumstances and charges following each other with frequen. with different substances. He caused cies up to one thousand millions in a water to be transported in this way by the second, a screen of blackened paper is per- electric current; in order to increase the fectly transparent, but if we raise the fre power of electricity upon metals, he diquency to five hundred million millions, the minished the cohesion of their molecules influence to be transmitted is light, and by heating the metals; and he studied the blackened paper becomes an almost also the relations between the transport of perfect screen.”+ As to the wonderful the molecules by electric stress, and the electrical effects produced by means of phenomena of phosphorescence. One currents alternating with very high fre. feels, especially when remembering the quency, such as they are produced by the speculations of the first half of this cenMontenegrin professor, Nikola Tesla, the tury (chiefly those of Séguin), that a new readers of this review have already been and most promising field is opened by familiarized with them in a preceding these researches; they raise a host of number (LIVING AGE, No. 2496, p. 309). questions relative to the most difficult Many more researches some of them parts of molecular mechanics.
The same must be said as regards mod. Drahtwellen," in Wiedemann's Annalen der Physik, ern research in chemistry. The work now 1891, vol. xlii., p. 405. Ritter and Rubens in same done is of two different kinds. While a periodical, vol. xl. 1890. MM. Sarasin and De la Rive having come to the conclusion that the vibrators send numerous army of laboratory workers acout a great number of undulations of various periods, cumulate heaps and heaps of minute facts, new researches were undertaken by Bjerknesscar. and study the properties of separate chem.
, 1891, t 27, p. 229), and they brought to light the so-called ical compounds without being guided by
dampening” of electrical undulations.ma question any general idea, a few chemists devote which also was discussed mathematically by Poincaré (Archives, t. 25, p. 609), and Perot (Comptes Rendus. themselves to the most intricate questions January 25, 1892). All the gases, many liquids, and many solids (glass, reactions and molecular structure. They
relative to the very substance of chemical gutta-percha, etc.) - all named dielectrics - offer á great resistance to the passage of electricity. A con- endeavor to bridge over the gulf between siderable expenditure of work is required for the pas: molecular physics and chemistry, and to sage of electricity, and the relative amounts of this expenditure in various bodies are measured by the so-called “dielectric constants." These constants, in * On some Test Cases for the Maxwell-Boltzmann Maxwell's theory, must be equal to the squares of the Doctrine regarding. Distribution of Energy, by Sir iodices of refraction of light. This prevision has now William Thomson, in Proceedings of the Royal Som proved to be true for paraffin in three different states, ciety, vol. l., No. 302, p. 79. glass, resin, oil, olive-oil, xylol, and petroleum. (An- † Philosophical Magazine, 1890, vol. xxix. ; Pro nalen der Physik, 1891 and 1892, vols. xlii. and xliv.) ceedings of the Royal Society, January 15, 1891.
† Proceedings of the Royal Society, April 1, 1891, 1 Annalen der Physik, 1892, Bd. 45, p. 28. vol. xlix., p. 418.
Ś Proceedings of the Royal Society, vol. 1., p. 87.