Part 62

Now the electron which is revolving around the positive nucleus of a hydrogen atom, must, according to electrodynamic laws, radiate energy. This radiation will act as a resistance to its motion, causing its orbit to become smaller and its frequency to increase. Hence luminous hydrogen would be expected to give off a continuous spectrum. The very fine lines actually found seem inexplicable on the classical dynamical and electrodynamical theories. These lines, and those of many other spectra, may even be grouped into series, and the relations between them expressed in mathematical form. Formulæ have been proposed by Balmer, Rydberg, Ritz and others, all of which contain a universal constant N as well as certain parameters which must be varied by unity in passing from one line of a series to the next.

In 1913 Bohr proposed anatomic theory which brings to light a remarkable numerical relationship between this quantity N and Planck’s constant h. He postulated that the electron in the hydrogen atom, for instance, cannot revolve in a circle of any arbitrary radius, but is confined to those orbits for which its kinetic energy is an integral multiple of ½hn, n being its orbital frequency. Now at times this electron is supposed to jump from an outer to an inner orbit, when the excess energy of the first orbit over the second is radiated away. But the energy emitted is also taken to be equal to hν, where ν is the frequency of the radiation. Hence ν can be determined, and the expression obtained for it is exactly that given long before by Balmer as an empirical law. The most remarkable thing about it, however, is that Bohr’s result contains a constant involving h and the electronic charge and mass which has precisely the value of the universal constant N of Balmer’s and Rydberg’s formulæ. In all, the theory accounts for three series of hydrogen, and yields satisfactory results for helium atoms which have lost an electron, or lithium atoms which have a double positive charge. But for atoms which retain more than a single electron it seems no longer to hold.

The three mentioned are only the most clearly defined of a growing group of phenomena in which the quantum manifests itself. Its significance and the alteration in our fundamental conceptions to which it seems to be leading is for the future to make clear. That it presents the most important and interesting problem as yet unsolved few physicists would deny.

American Physicists.—In attempting to cover the progress of physics during the last hundred years in the space of a few pages, many important developments of the subject have of necessity remained untouched, and the treatment of many others has been entirely inadequate. Among those appearing in the Journal of which no mention has been made are LeConte’s (=25=, 62, 1858) discovery of the sensitive flame and Rood’s (=46=, 173, 1893) invention of the flicker photometer. However, enough has been recounted to indicate the preeminent position in the history of physics in America occupied by four men: Joseph Henry, of the Albany Academy, Princeton, and the Smithsonian Institution; Henry Augustus Rowland, of Johns Hopkins University; Josiah Willard Gibbs, of Yale; and Albert Abraham Michelson, of the United States Naval Academy, Case School of Applied Science, Clark University, and the University of Chicago. Of these, the last named has the distinction of being the only American physicist to have received the Nobel prize, though there is little doubt that the other three would have been similarly honored had not their important work been published prior to the institution of this award. All four occupy high places in the ranks of the world’s great men of science, and the investigations carried out by them and their fellow workers in America have given to their country a position in the annals of physics which is by no means insignificant.

The Journal’s Part in Meteorology.

The meteorological investigations published in the early numbers of the Journal have played an important role in establishing a correct theory of storms. Before the origin of the United States Signal Service in 1871 no systematic weather reports were issued by any governmental agency in this country, and consequently the work of collecting as well as interpreting meteorological data rested entirely in the hands of interested individuals and institutions. The earliest important studies of storms to appear in the Journal were contributed by Redfield of New York, whose first paper (=20=, 17, 1831) treated in considerable detail a violent storm which passed over Long Island, Connecticut and Massachusetts in 1821. He concluded that “the direction of the wind at a particular place, forms no part of the essential character of a storm, but is only incidental to that particular portion ... of the track of the storm which may chance to become the point of observation, ... the direction of the wind being, in all cases, compounded of both the rotative and progressive velocities of the storm.” A few years later, analyses of twelve “gales and hurricanes of the Western Atlantic” (=31=, 115, 1837) led to the statement that the phenomena involved “are to be ascribed mainly to the mechanical gravitation of the atmosphere, as connected with the rotative and orbital movements of the earth’s surface.” In this paper is emphasized the fact that the wind may blow in diametrically opposite directions at points near the storm center. “While one vessel has been lying-to in a heavy gale of wind, another, not more than thirty leagues distant, has at the very same time been in another gale equally heavy, and lying-to with the wind in quite an opposite direction.” From an accompanying sketch showing wind directions, the reader would infer that, at this time, Redfield believed the motion of the air to be very nearly in circles about the storm center. The same idea is conveyed by a later paper (=42=, 112, 1842). Espy (=39=, 120, 1840) of Philadelphia, however, claimed that observation showed rather that the wind blew inwards toward a central point, if the storm were round in shape, or toward a central line, if it were oblong. This view Redfield (=42=, 112, 1842) contested, and brought forth much evidence to prove its falsity. A later statement (=1=, 1, 1846) of his own theory is as follows: “I have never been able to conceive, that the wind in violent storms moves only in circles. On the contrary, a vortical movement ... appears to be an essential element of their violent and long-continued action, of their increased energy towards the center or axis, and of the accompanying rain.... The degree of vorticular inclination in violent storms must be subject, locally, to great variations; but it is not probable that, on an average of the different sides, it ever comes near to forty-five degrees from the tangent of a circle,—and that such average inclination ever exceeds two points of the compass, may well be doubted.” A qualitative explanation of the effect of the earth’s rotation on the direction of the wind near the storm center had already been given by Tracy (=45=, 65, 1843), and this was followed some years later by Ferrel’s (=31=, 27, 1861) very thorough quantitative investigation of the dynamics of the atmosphere.

A number of individuals kept systematic records of meteorological observations, among whom was Loomis, whose storm analyses did much to settle the merits of the rival theories of Redfield and Espy. In studying the storm of 1836 (=40=, 34, 1841) he had drawn on the map lines through those points in the track of the storm where the barometer, at any given hour, is lowest. While this method revealed the general direction in which the storm was progressing, it failed to give much indication of its size or shape. In discussing the two tornadoes of February, 1842, one of which had already been described in the Journal (=43=, 278, 1842), he adopted a new and more illuminating graphical method. Instead of connecting points of lowest pressure, he drew a curve through all points where the barometer stood at its normal level, then one through those points at which the pressure was ²⁄₁₀ of an inch below normal, and so on. Temperature he treated in much the same way, and the strength and direction of the wind were indicated by arrows. This innovation gave to his storm analyses a significance which had been entirely lacking in those of his predecessors, and led to the familiar systems of isobars and isotherms in use on the daily charts issued by the Weather Bureau at the present time. Loomis advocated careful observations for one year at stations 50 miles apart all over the United States, so that sufficient data might be obtained to settle once for all the law of storms. His efforts, seconded by those of Henry, Bache, Pierce, Abbe, and Lapham, led eventually to the establishment of the Signal Service, and the publication of daily weather maps according to the plan advocated thirty years before. These maps afforded a basis for further analyses of storms, which he published in numerous “Contributions to Meteorology” (=8=, 1, 1874, et seq.) between 1874 and his death in 1890.

In addition to his work on storms, Loomis made a careful study of the earth’s magnetism (=34=, 290, 1838 et seq.), and of the aurora borealis (=28=, 385, 1859 et seq.). That a connection existed between sunspots, aurora, and terrestrial magnetism was already recognized. Loomis (=50=, 153, 1870 et seq.), however, showed that the periodicity of the aurora borealis, as well as of excessive disturbances in the earth’s magnetic field, corresponds very closely with that of sunspots.

Notes.

Footnote 154:

J. W. Gibbs, Trans. Conn. Acad. Arts and Sci., =3=, 108 and 343. Abstract by the author, the Journal, =16=, 441, 1878.

Footnote 155:

H. K. Onnes, Nature, =93=, 481, 1914.

Footnote 156:

H. Hertz, Wied. Ann., =34=, 551, 1888 et seq.

Footnote 157:

E. F. Nichols and G. F. Hull, Phys. Rev., =13=, 307, 1901 et seq.

Footnote 158:

J. J. Thomson, Phil. Mag., =44=, 293, 1897.

Footnote 159:

R. A. Millikan, Phys. Rev., =2=, 109, 1913.

Footnote 160:

P. Zeeman, Phil. Mag., =43=, 226, 1897.

Footnote 161:

H. A. Lorentz, Phil. Mag., =43=, 232, 1897.

Footnote 162:

S. J. Barnett, Phys. Rev., =6=, 239, 1915, and =10=, 7, 1917.

Footnote 163: