Physicists From Germany

"Let E \partial \lambda be the intensity of the component polarized in a, or... [equivalently] the increase, which the vis viva of the ether beyond the screen S2 experiences through this component in the unit of time."

"A perfect mirror, like every diathermanous body, can itself send out no rays; for if it did (confined in an enclosure of like temperature) it would warm this enclosure... and cool itself more and more."

"[N]one of the gases giving line spectra at temperatures heretofore used, do so by simple , but essentially by luminescent actions (chemical, electrical, and photogenic), so... we cannot, in general, apply the law of Kirchhoff of the proportionality between radiation and absorption to either terrestrial or celestial substances. In these cases the principle of usually holds, since in luminescence the radiation of line spectra is accompanied by selective absorption of the same spectral lines, so that the law may be used qualitatively, which is... the way Kirchhoff and Bunsen... attempted to confirm it."

"[I]t will be assumed that perfectly diathermanous bodies are conceivable, that is, such which will absorb none of the incident heat rays of whatever nature these may be, and finally, that a perfect mirror is conceivable, i.e., a body which reflects completely all heat rays."

"The quantity E is called the emissive power of the body."

"[I]n certain cases an exception to this rule may occur... [when] absorption and the radiation produce other changes in the body.., for example in bodies... chemically changed by light... [etc.]"

"Such cases should be excluded on the assumption that neither by means of the rays which it radiates or absorbs, nor by... other influences... does the body... change, if its is kept constant by the addition or the subtraction of heat. Under these conditions... the... heat... transferred to a body in a given time to prevent cooling... in consequence of its radiation, is equivalent to the vis viva of the emitted rays; and the amount of heat... withdrawn... to counterbalance the heating from absorption of radiations, is equivalent to the vis viva of the absorbed rays."

"Let a body which satisfies these conditions be surrounded by an enclosure, having the same temperature [and kept constant], through which no heat rays can penetrate... The body sends out heat rays and is encountered by... heat rays... in part... from the enclosure, in part... thrown back... by reflection from it, absorbing a part of them. Its temperature must thus remain the same, unless heat is withdrawn from it or communicated to it as follows on the principle from which Carnot's law results. For this reason the vis viva of the rays, which it sends out in a certain time, must equal the vis viva of the rays which it absorbs in the same time."

"Through the radiations... a body sends out, the quantity of ... it contains will... sustain a loss... equivalent to the ' of those rays, and through the heat rays... it absorbs, a gain... equivalent to the vis viva of the absorbed rays."

"Heat rays have the same nature as light rays... The invisible heat rays are distinguished from light rays only by the period of or the wave length."

"All heat rays follow the same laws in their propagation, which are known for light rays."

"This investigation will be... simplified if we imagine the enclosure... composed... of bodies which, for infinitely small thickness, completely absorb all rays which fall upon them. I... call such bodies perfectly black, or more briefly, black."

"Of the heat rays... sent... to a body by its surroundings a part are absorbed, the others are... varied by reflection and . The rays refracted and reflected... pass off... with those sent out by it, without... mutual disturbance..."

"Look here, I have succeeded at last in fetching some gold from the sun."

"A '... must have the same as the medium... then there will be no reflection at its surface, and all incident rays... wholly absorbed."

"[R]adiation in empty space will be investigated..⇒ the [associated] black bodies must have a refracted index which differs infinitely little from 1."

"Before we can rightly understand the principles of spectroscopic astronomy, we must go back to the life and work of its founder—Joseph von Fraunhofer. ...Allowing light from the Sun to pass through a prism attached to the telescope, he was amazed to find several dark lines in the spectrum. ...Fraunhofer named the more prominent lines by the letters of the alphabet from A in the red to H in the violet. They are now known as the Fraunhofer lines. ...He expressed the belief that the pair of lines in the solar spectrum which he marked D, coincided with the pair of bright lines emitted by incandescent sodium. Although he doubtless suspected that the lines conveyed intelligence regarding the elements in the Sun, he never was able properly to decipher their meaning. Had he lived he would probably have made the great discovery."

"Fraunhofer discovered that the apparent continuity of a rainbow is an illusion. There are tiny gaps, dim or black arcs of missing colors, too narrow for us to see in the glare of natural rainbows. To say it another way, there are specific colors (specific wavelengths of light) in which sunlight is deficient. Fraunhofer eventually catalogued 576 of these gaps, or "absorption lines": 576 specific wavelengths missing from sunlight. Fraunhofer's career of discovery was cut short by consumption."

"By his invention of new and improved methods, machinery, and measuring instruments for grinding and polishing lenses, by his having the superintendence, after 1811, also of the work in glass-melting, enabling him to produce flint and crown glass in larger pieces, free of veins, but especially by his discovery of a method of computing accurately the forms of lenses, he has led practical optics into entirely new paths, and has raised the achromatic telescope to, until then, undreamed of perfection."

"Modern physics often advances only by sacrificing some of our traditional philosophical convictions."

"Fraunhofer had busied himself with glass his entire life. Working with glass was his family tradition, and the manufacture of optical lenses and prisms was his life."

"Fraunhofer's secrets of manufacture accompanied him to the grave. His artisanal knowledge was such that, after his death, even the apprentices who worked with him, in the same glass hut and with the same equipment, achieved only limited success in the manufacture of optical glass."

"Fraunhofer's publication of 1814 did not receive prompt recognition, nor did his papers of 1821 and 1823. Physicists were fighting over the emission and wave theories of light. The attention of chemists was concentrated upon Dalton's atomic theory and the Berthollet-Proust controversy over the law of definite proportions. The full explanation of the new fact brought forth by Fraunhofer was not given for nearly forty years. He himself had failed to find the key to the hieroglyphics of the solar lines, the "Fraunhofer lines," nor had he clearly defined the role which the spectral lines were destined to play in chemical analysis."

"Whether Newton saw the lines or not, he seems to have paid no especial heed to them. In the year 1802, Dr. W. H. Wollaston using, a slit one-twentieth of an inch in width, noted at least four fine dark lines crossing the solar spectrum. Supposing them to be merely 'natural boundaries' of the different colour-bands, he too inquired no further; and there still for a while the matter rested. Nobody yet suspected, even vaguely, what great future results lay enfolded in the casual discovery of these few slight lines. Not many years later the matter was taken up by Fraunhofer, an able German optician."

"He was the first to observe spectra due to gratings, and with them he made the earliest determination of wave-lengths."

"He must have been working quietly at the problem through years of European war and tumult. Crowned heads rose and fell; and nations changed hands; and tyrants were cast down; and brave men died by thousands for their countries; whilst Fraunhofer, in the midst of national seethings, calmly investigated the nature of black lines in sunlight."

"In order to receive in the eye all the light diffracted through a narrow opening, and to see the phenomena strongly magnified; still more in order to directly measure the inflection of the light, I placed in front of the objective of a theodolite-telescope a screen in which there was a narrow vertical opening which could be made wider or narrower by means of a screw. By means of a heliostat I threw sunlight into a darkened room through a narrow slit so that it fell upon this screen, through whose opening the light was therefore diffracted. I could then observe through the telescope the phenomena produced by the diffraction, magnified, and yet seen with sufficient brightness; and at the same time I could measure the angles of inflection of the light by means of the theodolite."

"It will reward enough for me if, by the publication of the present experiment, I have directed the attention of investigators to this subject, which still promises much for physicial optics and appears to open a new field."

"With patience he went into the question, using the telescope as well as a very narrow slit... Close examination was rewarded by the making out of lines upon lines; till in the year 1814, that which witnessed the downfall of Napoleon and his banishment to Elba, Fraunhofer had mapped three or four hundred."

"I wished to find out whether a similar bright line could be seen in the spectrum of sunlight as in the spectrum of lamplight, and I found, with the telescope, instead of this, an almost countless number of strong and feeble vertical lines which, however, were darker than the other parts of the spectrum, some appearing to be almost perfectly black."

"Since the violet rays through the objective of the theodolite telescope have a shorter focal length than the red rays, it is evident why the eye-piece must be displaced in order to see plainly the lines in the different colors."

"In all my experiments I could, owing to lack of time, pay attention to only those matters which appeared to have a bearing upon practical optics. I could either not touch other questions, or at most not follow them very far. Since the path thus traced in optical experiments seems to promise to lead to interesting results, it is greatly to be desired that skilled investigators should devote attention to it."

"Up to the present time, in experiments on diffraction there has been no instrument, except a magnifying-glass, which could be used with profit; and this may perhaps be one of the reasons why in this field of physical optics we are so backward, and why we know so little of the laws of this modification of light."

"The number of different optical phenomena has become in our time so great that caution must be taken so as to avoid being deceived, and also to refer the phenomena to the simple laws."

"Fraunhofer made a great many experiments connected with these mysterious lines, anxious to discover, if possible, their meaning, For although he now saw the lines, which had scarcely so much as been seen before, he could not understand them; he could not read what they said. They spoke to him, indeed, about the Sun, but they spoke in a foreign language, the key to which he did not possess."

"Heinrich Hertz seemed to be predestined to open up to mankind many of the secrets which nature has hitherto concealed from us; but all these hopes were frustrated by the malignant disease which, creeping slowly but surely on, robbed us of this precious life and of the achievements which it promised."

"Although experimenters had attempted by various means to submit Maxwell's views to a test, the technical difficulties were so great that no success had been achieved. It appeared clearly from Maxwell's equations that no appreciable effects could be anticipated unless dE/dt was very great; and this meant that the electric intensity E would have to vary with extreme rapidity. The simplest means of obtaining a result of this kind would be to produce an oscillating field of electric intensity in which the oscillations were extremely rapid, say, several millions per second. But no mechanical contrivance could yield such rapid vibrations, and... no other methods suggested themselves. ... In 1885 Helmholtz directed the attention of his pupil, Hertz, to the problem. Hertz was one of the most remarkable experimenters of the nineteenth century; he succeeded in at last vanquishing the technical difficulties and in generating by purely electrical means an oscillating electric field of extremely high frequency. Electromagnetic waves of sufficient intensity were thus produced; and after having been sidetracked for a time by a secondary phenomenon whose nature was elucidated by Poincaré, Hertz verified the fact that the waves advanced with the speed of light and indeed possessed all the essential properties of light waves other than those of visibility to the human eye. Thus, as a result of Hertz's experiments, the foundations were laid for the commercial use of wireless and radio; but, more important still, Maxwell's electromagnetic theory of light establishing the intimate connection between electricity and optics had been at last vindicated."

"If the idea of physical reality had ceased to be purely atomic, it still remained for the time being purely mechanistic; people still tried to explain all events as the motion of inert masses; indeed no other way of looking at things seemed conceivable. Then came the great change, which will be associated for all time with the names of Faraday, Clerk Maxwell, and Hertz."

"It is not particularly satisfactory to see equations set forth as direct results of observation and experiment, where we used to get long mathematical deductions as apparent proofs of them. Nevertheless, I believe that we cannot, without deceiving ourselves, extract much more from known facts than is asserted in the papers referred to. If we wish to lend more color to the theory, there is nothing to prevent us from supplementing all this and aiding our powers of imagination by concrete representations of the various conceptions as to the nature of electric polarisation, the electric current, etc."

"When a constant electric current flows along a cylindrical wire, its strength is the same at every part of the section of the wire. But if the current is variable, self-induction produces a deviation from this... induction opposes variations of the current in the centre of the wire more strongly than at the circumference, and consequently the current by preference flows along the outer portion of the wire. When the current changes its direction... this deviation increases rapidly with the rate of alternation; and when the current alternates many million times per second, almost the whole of the interior of the wire must, according to theory, appear free from current, and the flow must confine itself to the very skin of the wire. Now in such extreme cases... preference must be given to another conception of the matter which was first presented by Messrs. 0. Heaviside and J. H. Poynting, as the correct interpretation of Maxwell's equations as applied to this case. According to this view, the electric force which determines the current is not propagated in the wire itself, but under all circumstances penetrates from without into the wire, and spreads into the metal with comparative slowness and laws similar to those which govern changes of temperature in a conducting body. ...Inasmuch as I made use of electric waves in wires of exceedingly short period in my experiments on the propagation of electric force, it was natural to test by means of these the correctness of the conclusions deduced. As a matter of fact the theory was found to be confirmed by the experiments..."

"One cannot escape the feeling that these mathematical formulas have an independent existence and intelligence of their own, that they are wiser than we are, wiser even than their discoverers, that we get more out of them than was originally put into them."

"The difficult surface conditions met with when light passes from one medium to another, including such subjects as ellipticity, total reflection, etc., have been critically discussed among others by Neumann (1835) and Rayleigh (1888) but the discrimination between the Fresnel and the Neumann vector was not accomplished without misgiving before the advent of the work of Hertz. It appears... that the elastic theories of light, if Kelvin's gyrostatic adynamic ether be admitted, have not been wholly routed. Nevertheless the great electromagnetic theory of light propounded by Maxwell (1864, 'Treatise,' 1873) has been singularly apt not only in explaining all the phenomena reached by the older theories and in predicting entirely novel results, but in harmoniously uniting as parts of a unique doctrine, both the electric or photographic light vector of Fresnel and Cauchy and the magnetic vector of Neumann and MacCullagh. Its predictions have, moreover, been astonishingly verified by the work of Hertz (1890), and it is to-day acquiring added power in the convection theories of Lorentz (1895) and others."

"Erwin with his psi can do Calculations quite a few. But one thing has not been seen: Just what does psi really mean?"

"The rigour of science requires that we distinguish well the undraped figure of Nature itself from the gay-coloured vesture with which we clothe her at our pleasure."

"The subject of electric oscillation announced in a remarkable paper of Henry in 1842 and threshed out in its main features by Kelvin in 1856, followed by Kirchhoff's treatment of the transmission of oscillations along a wire (1857), has become of discriminating importance between Maxwell's theory of the electric field and the other equally profound theories of an earlier date. These crucial experiments contributed by Hertz (1887, et seq.) showed that electromagnetic waves move with the velocity of light, and like it are capable of being reflected, refracted, brought to interference and polarized. A year later Hertz (1888) worked out the distribution of the vectors in the space surrounding the oscillatory source. ...Some doubt was thrown on the details of Hertz's results by Sarasin and de la Rive's phenomenon of multiple resonance (1890), but this was soon explained away as the necessary result of the occurrence of damped oscillations by Poincaré (1891), by Bjerknes (1891) and others."

"It's of no use whatsoever. This is just an experiment that proves Maestro Maxwell was right—we just have these mysterious electromagnetic waves that we cannot see with the naked eye. But they are there."

"A simple calculation shows that from the classical theory follows that we should find a broadening of the beam with the maximum intensity on the place of the beam without field. However, from the quantum theory follows that we should find there no intensity at all, and deflected molecules on both sides. The beam should split up in two beams corresponding to the two orientations of the magnet. The experiment decided in favor of the quantum theory."

"In his obituary for Stern wrote: “Some of Pauli’s great theoretical contributions came from Stern’s suggestions, or rather questions; for example, the theory of magnetism of free electrons in metals.” From and Armin Telling – Pauli’s last two assistants – I have learned that Pauli has also discussed the question of extensively with Stern during his Hamburg time, before the advent of the new quantum mechanics."

""Shall we do it?" "Well, then let's go, we shall do it!" Otto Stern asking, Walther Gerlach answering."

"In 1888... Heinrich Hertz succeeded in producing electromagnetic waves (to which he subsequently gave the shorter name of electric waves) standing in free space and gliding over wires; he showed that they could be reflected, refracted, polarized, diffused, and generally followed optical laws just as though they were light waves. This achievement was the first real advance toward the art of wireless telegraphy. As a detector of electric waves at a distance from whence they were emitted, Hertz employed a circlet of wire having an air gap in it of microscopic size; this he termed a "resonator." The distance to which waves could be detected with it was very limited, but it served Hertz's purpose admirably. ... Any theory advanced must conform with Maxwell's conceptions and the experiments of Hertz, but as the fundamental equations by which Maxwell evolved his theory are as broad as they are beautiful, its interpretations by various technicians are widely divergent, and the final solution is rendered all the more difficult when Hertz's work is consulted; for he not only observed electric waves in free space, but waves which traverse the surface of wires as well."