vided into three classes-the 'regular attending students,' students for lectures only, and lecture-visitors. As regular students, without any exception, such young men will be accepted who have acquired the knowledge necessary for being admitted into any university, said knowledge to have been acquired at a German Gymnasium,' a German 'Oberrealschule' (a high school in which sciences as well as art and languages are taught), a Bavarian 'industrial school,' or the Saxonian Polytechnical Academy of Chemnitz. As to foreigners, the ministry of ecclesiastical affairs and public education is to decide whether their scholastic erudition is sufficient to admit them. German subjects, other than Prussian, will be admitted under the same conditions as Prussian subjects. As students admitted to hear the lectures only (i. e., without privilege of being graduated by the board of examiners), young men will be admitted, not possessed of the education necessary for being admitted into a German university, but having acquired the schooling necessary for performing only one year's military service. The admission of such students is put into the hands of the rector of the technical high school. As lecture visitors such persons may be admitted to the lectures or demonstrations who are not eligible to either of the two classes just mentioned. The admission of lecture visitors will be granted by the rector, with the consent of the proper professor. There is particularly one new restriction in these regulations, viz., that all encouragements for foreigners are dropped. Setting aside the lecture visitors, only such foreigners will be admitted as are capable of complying with the German educational requirements or who are in possession of an equivalent foreign certificate of learning.

UNIVERSITY AND EDUCATIONAL NEWS. ANNOUNCEMENT is made of an anonymous gift to the Lebanon Valley College, Annville, Pa., of a hall of science to cost $80,000. Work on the building is to begin at once.

MR. E. G. BAWDEN, London, has entrusted Mr. Edgar Speyer with a sum in cash and securities of about £100,000 to be applied to

purposes of charity and benevolence, and for the advancement of knowledge, especially in aid of human suffering.' This sum has been apportioned for various purposes in the form of capital to be vested in trustees, and to be known in each case as the 'Bawden Fund.' The largest allotment is £16,000 to complete the sum of £200,000 required to bring about the incorporation of the University College in the University of London.

GIRTON COLLEGE, Cambridge, has received £2,000 by the will of Miss Elizabeth A. Manning.

AN imperial ukase has been issued at St. Petersburg, granting a liberal measure of autonomy to universities, pending the elaboration of permanent regulations. This is expected to ensure the opening of the universities and the resumption of the educational life of Russia, which has been at a stand still since February. The ukase places the election of rectors and deans of the universities, who have hitherto been appointed by the minister of education, in the hands of the university professors. The duty of seeing that academic life follows a normal and orderly course is entrusted by the ukase to professorial councils, to which has been confided jurisdiction over offences by students.

DR. CHASE PALMER, for some years professor of chemistry at the Central University of Kentucky, has accepted the position of professor of chemistry in the State College at Lexington, Ky., Dr. J. H. Kastle, who occupied the latter position, having recently gone to Washington as chief of the division of chemistry in the Hygienic Laboratory of the Marine Hospital Service.

DR. FRIEND E. CLARK, who has for two years been instructor in industrial chemistry in the Pennsylvania State College, has been appointed professor of chemistry in the Central University of Kentucky, at Danville.

DR. J. BENDIXSON has been elected professor of mathematics in the University of Stockholm.

DR. OSKAR BREFELD, professor of botany at Breslau, has retired owing to failing eyesight.

Kirchhoff (1882, 1883), profoundly modified the classic treatment. Airy (1834,

1838) and others elaborately examined the diffraction due to a point source in view of its important bearing on the efficiency of optical instruments.

A unique development of diffraction is the phenomenon of scattering propounded by Rayleigh (1871) in his dynamics of the blue sky. This great theory which Rayleigh has repeatedly improved (1881, et seq.) has since superseded all other relevant explanations.

POLARIZATION.

An infinite variety of polarization phenomena grew out of Bartholinus's (1670) discovery. Sound beginnings of a theory were laid by Huyghens (Traité,' 1690), whose wavelet principle and elementary wave front have persisted as an invaluable acquisition, to be generalized by Fresnel in 1821.

Fresh foundations in this department of optics were laid by Malus (1810) in his discovery of the cosine law and the further discovery of the polarization of reflected light. Later (1815) Brewster adduced the conditions of maximum polarization for this case.

In 1811 Arago announced the occurrence of interferences in connection with parallel plane-polarized light, phenomena which under the observations of Arago and Fresnel (1816, 1819), Biot (1816), Brewster (1813, 1814, 1818) and others grew immensely in variety, and in the importance of their bearing on the undulatory theory. It is on the basis of these phenomena that Fresnel in 1819 insisted on the transversality of light waves, offering proof which was subsequently made rigorous by Verdet (1850). Though a tentative explanation was here again given by Young (1814), the first adequate theory of the behavior of

thin plates of aeolotropic media with polarized light came from Fresnel (1821).

Airy (1833) elucidated a special case of the gorgeously complicated interferences obtained with convergent pencils; Neumann in 1834 gave the general theory. The forbidding equations resulting were geometrically interpreted by Bertin (1861, 1884), and Lommel (1883) and Neumann (1841) added a theory for stressed media, afterwards improved by Pockels (1889).

The peculiarly undulatory character of natural light owes its explanation largely to Stokes (1852), and his views were verified by many physicists, notably by Fizeau (1862) showing interferences for path differences of 50,000 wave-lengths and by Michelson for much larger path differences.

The occurrence of double refraction in all non-regular crystals was recognized by Haüy (1788) and studied by Brewster (1818). In 1821, largely by a feat of intuition, Fresnel introduced his generalized elementary wave surface, and the correctness of his explanation has since been substantiated by a host of observers. Stokes (1862, et seq.) was unremittingly active in pointing out the theoretical bearHamilton ing of the results obtained. (1832) supplied a remarkable criterion of the truth of Fresnel's theory deductively, in the prediction of both types of conic refraction. The phenomena were detected experimentally by Lloyd (1833).

The domain of natural rotary polarization, discovered by Arago (1811) and enlarged by Biot (1815), has recently been placed in close relation to non-symmetrical chemical structure by LeBel (1874) and van't Hoff (1875), and a tentative molecular theory was advanced by Sohncke (1876).

Boussinesq (1868) adapted Cauchy's theory (1842) to these phenomena. Independent elastic theories were propounded

by MacCullagh (1837), Briot, Sarrau (1868); but there is naturally no difficulty in accounting for rotary polarization by the electromagnetic theory of light, as was shown by Drude (1892).

Among investigational apparatus of great importance the Soleil (1846, 1847) saccharimeter may be mentioned.

THEORIES.

In conclusion, a brief summary may be given of the chief mechanisms proposed to account for the undulations of light. Fresnel suggested the first adequate optical theory in 1821, which, though singularly correct in its bearing on reflection and refraction in the widest sense, was merely tentative in construction. Cauchy (1829) proposed a specifically elastic theory for the motion of relatively long waves of light in continuous media, based on a reasonable hypothesis of molecular force, and deduced therefrom Fresnel's reflection and refraction equations. Green (1838), ignoring molecular forces and proceeding in accordance with his own method in elastics, published a different theory, which did not, however, lead to Fresnel's equations. Kelvin (1888) found the conditions implied in Cauchy's theory compatible with stability if the ether were considered as bound by a rigid medium. The ether implied throughout is to have the same. elasticity everywhere, but to vary in density from medium to medium, and vibration to be normal to the plane of polarization.

Neumann (1835), whose work has been reconstructed by Kirchhoff (1876), and MacCullagh (1837), with the counterhypothesis of an ether of fixed density but varying in elasticity from medium to medium, also deduced Fresnel's equations, obtaining at the same time better surface conditions in the case of æolotropic media.

The vibrations are in the plane of polarization.

All the elastic theories essentially predict a longitudinal light wave. It was not until Kelvin in 1889, 1890 proposed his remarkable gyrostatic theory of light, in which force and displacement become torque and twist, that these objections to the elastic theory were wholly removed. MacCullagh, without recognizing their bearing, seems actually to have anticipated Kelvin's equation.

With the purpose of accounting for dispersion, Cauchy in 1835 gave greater breadth to his theory by postulating a sphere of action of ether particles commensurate with wave-length, and in this direction he was followed by F. Neumann (1841), Briot (1864), Rayleigh (1871) and others, treating an ether variously loaded with material particles. Among theories beginning with the phenomena observed, that of Boussinesq (1867, et seq.) has received the most extensive development.

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, therefore, 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.

ELECTROSTATICS.

Coulomb's (1785) law antedates the century; indeed, it was known to Cavendish (1771, 1781). Problems of electric distribution were not seriously approached, however, until Poisson (1811) solved the case for spheres in contact. Afterwards Clausius (1852), Helmholtz (1868) and Kirchhoff (1877) examined the conditions for discs, the last giving the first rigorous theory of the experimentally important plate condenser. In 1845, 1848 the investigation of electric distribution received new incentive as an application of Kelvin's beautiful method of images. Maxwell ("Treatise,' 1873) systematized the treatment of capacity and induction coefficients.

Riess (1837) in a classic series of experiments on the heat produced by electrostatic discharge virtually deduced the potential energy of a conductor and in a measure anticipated Joule's law (1841). In 1860 appeared Kelvin's great paper on the electromotive force needed to produce a spark. As early as 1855, however, he had shown that the spark discharge is liable to be of the character of a damped vibration and the theory of electric oscillation was subsequently extended by Kirchhoff (1867). The first adequate experimental verification is due to Feddersen (1858, 1861).

The specific inductive capacity of a medium with its fundamental bearing on the character of electric force was discovered by Faraday in 1837. Of the theories propounded to account for this property the most far reaching is Maxwell's (1865),

which culminates in the unique result showing that the refraction index of a medium is the square root of its specific inductive capacity. With regard to Maxwell's theory of the Faraday stress in the ether as compared with the subsequent development of electrostriction in other media by many authors, notably by Boltzmann (1880) and by Kirchhoff (1885), it is observable that the tendency of the former to assign concrete physical properties to the tube of force is growing, particularly in connection with radioactivity. Duhem (1892, 1895) insists, however, on the greater trustworthiness of the thermodynamic potential.

The seemingly trivial subject of pyroelectricity interpreted by Epinus (1756) and studied by Brewster (1825), has none the less elicited much discussion and curiosity, a vast number of data by Hankel (1839-93) and others and a succinct explanation by Kelvin (1860, 1878). Similarly piezoelectricity, discovered by the brothers Curie (1880), has been made the subject of a searching investigation by Voigt (1890). Finally Kerr (1875, et seq.) observed the occurrence of double refraction in an electrically polarized medium. Recent researches, among which those of Lemoine (1896) are most accurate, have determined the phase difference corresponding to the Kerr effect under normal conditions, while Voigt (1899) has adduced an adequate theory.

Certain electrostatic inventions have had a marked bearing on the development of electricity. We may mention in particular Kelvin's quadrant electrometer (1867) and Lippmann's capillary electrometer (1873). Moreover, among apparatus originating in Nicholson's duplicator (1788) and Volta's electrophorus, the TöplerHoltz machine (1865-67), with the recent improvement due to Wimshurst, has