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The Progress of Physics in the Nineteenth

l'entury, I: PROFESSOR CARL BABUS..... 353

Scientific Books :-

de Vries's Species and Varieties: PRO-
Theoretical Chemistry: PROFESSOR HARRY
C. JONES ....

............ 369

Scientific Journals and Articles ...........

Special Articles :

Skull and Skeleton of Sauropodous Dinosaurs, Jorosaurus and Brontosaurus: H. F. 0. The Drumming of the Drum-fishes : DR. Hugu M. SMITH .................... 374

have endeavored, in so far as I have been able, to meet the grave responsibilities implied in your invitation; yet had I but thought of the overwhelmingly vast territory to be surveyed, I well might have hesitated to embark on so hazardous an undertaking. To mention merely the names of men whose efforts are linked with splendid accomplishments in the history of modern physics would far exceed the time allotted to this address. To bear solely on certain subjects, those for instance with which I am more familiar, would be to develop an unsymmetrical picture. As this is to be avoided, it will be necessary to present a straightforward compilation of all work above a certain somewhat vague and arbitrary lower limit of importance. Physics is, as a rule, making vigorous though partial progress along independent parallel lines of investigation, a discrimination between which is not possible until some cataclysm in the history of thought ushers in a new era. It will be essential to abstain from entering into either explanation or

Peter Artedi: DR. CHARLES R. EASTMAN.... 378

Declaration of the National Educational

Association at the Asbury Park Meeting.. 379

Scientific Notes and News ........

............ 380

I'nirersity and Educational News........... 384

MSS. intended for publication and books, etc., intended for review should be sent to the Editor of SCIENCE, Garri. con-On-Andson, N. Y.



1. Mr. President, Ladies and Gentlemen: You have honored me by requesting at my hands an account of the advances made in physics during the nineteenth century. I

* Paper read at the International Congress in St. Louis.

familiar with the details of the subjects to be treated. I can neither. popularize nor can I endeavor, to entertain, except in so far as a rapid review of the glorious conquests of the century may be stimulating.

In spite of all this simplicity of aim, there is bound to be distortion. In any brief account, the men working at the beginning of the century, when investigations were few and the principles evolved necessarily fundamental, will be given greater consideration than equally able und abler investigations near the close, when workers (let us be thankful) were many, and the subjects lengthening into detail. Again, the higher order of genius will usually be additionally exalted at the expense of the less gifted thinker. I can but regret that these are the inevitable limitations of the cursory treatment prescribed. As time rolls on the greatest names more and more fully absorb the activity of a whole epoch.

METROLOGY. Finally, it will hardly be possible to consider the great advances made in physics except on the theoretical side. Ofrenowned experimental researches, in particular of the investigations of the con stants of nature to a degree of ever increasing accuracy, it is not practicable to give any adequate account. Indeed, the refinement and precision now demanded have placed many subjects beyond the reach of individual experimental research, and have culminated in the establishment of the great national or international laboratories of investigation at Sèvres (1872), at Berlin (1887, 1890), at London (1900), at Washington (1901). The introduction of uniform international units in cases of the arts and sciences of more recent development is gradually, but inexorably, urging the same advantages on all. Finally, the access to adequate instruments of research has everywhere become an easier possibility for those duly qualified, and the institutions and academies which are systematically undertaking the distribution of the means of reasearch are continually increasing in strength and in number.

elastics, crystallography, capillarity, solution, diffusion, dynamics, viscosity, hy. drodynamics, acoustics; in thermometry, calorimetry, thermodynamics, kinetic theory, thermal radiation; in geometric optics, dispersion, photometry, fluorescence, photochemistry, interference, diffraction, polarization, optical media ; in electrostatics, Volta contacts, Seebeck contacts, electrolysis, electric current, magnetisin, electromagnetism, electrodynamics, induction, electric oscillation, electric field, radioactivity.

Surely this is too extensive a field for any one man! Few who are not physicists realize that each of these divisions has a splendid and voluminous history of development, its own heroes, its sublime classics often culled from the activity of several hundred years. I repeat that few understand the unmitigatedly fundamental character, the scope, the vast and profound intellectual possessions, of pure physics; few think of it as the one science into which all other sciences must ultimately converge -or a separate representation would have been given to most of the great divisions wh which I have named.

Hence even if the literary references may be given in print with some fullness, it is impossible to refer verbally to more than the chief actors and quite impossible to delineate sharply the real significance and the relations of what has been done. Moreover, the dates will in most instances have to be omitted from the reading. It has been my aim, however, to collect the greater papers in the history of physics, and the suggestion is implied that science would gain if by some august tribunal researches of commanding importance were formally canonized for the benefit of posterity.

CLASSIFICATION. In the present paper it will be advisable to follow the usual procedure in physics, taking in order the advances made in dynamics, acoustics, heat, light and electricity. The plan pursued will, there. fore, specifically consider, the progress in

ELASTICS. To begin with elasticity, whose development has been of such marked influ

ence throughout the whole of physics, we hands of Kelvin (1856), of Kirchhoff note that the theory is virtually a creation (1876), of Neumann (1885), leads to equaof the nineteenth century. Antedating tions with twenty-one constants for the Thomas Young, who in 1807 gave to the æolotropic medium reducing to two in the subject the useful conception of a modulus, simplest case. and who seems to have definitely recognized The wave motion in an isotropic medium the shear, there were merely the experi- was first deduced by Poisson in 1828, showmental contribution of Galileo (1638), ing the occurrence of longitudinal and Hooke (1660), Mariotte (1680), the elastic transverse waves of different velocities; curve of J. Bernoulli (1705), the elemen- the general problem of wave motion in tary treatment of vibrating bars of Euler æolotropic media, though treated by Green and Bernoulli (1742), and an attempted (1842), was attacked with requisite power analysis of flexure and torsion by Coulomb by Blanchet (1840-1842) and by Christof(1776).

fel (1877). The establishment of a theory of elas- Poisson also treated the case of radial ticity on broad lines begins almost at a vibrations of a sphere (1828), a problem bound with Xavier (1821), reasoning from which, without this restriction, awaited the a molecular hypothesis to the equation of solutions of Jaerisch (1879) and of Lamb elastic displacement and of elastic potential (1882). The theory of the free vibrations energy (1822–1827); yet this startling ad- of solids, however, is a generalization due vance was destined to be soon discredited to Clebsch (1857–58, ‘Vorlesungen,’ 1862). in the light of the brilliant generalizations Elasticity received a final phenomenal of Cauchy (1827). To him we owe the six advance through the long continued labors component stresses and the six component of de St. Venant (1839–55), which in the strains, the stress quadric and the strain course of his editions of the work of quadric, the reduction of the components Moigno, of Navier (1863), and of Clebsch to three principal stresses and three prin- (1864), effectually overhauled the whole cipal strains, the ellipsoids and other of subject. IIe was the first to adequately the indispensable conceptions of the present assert the fundamental importance of the day. Cauchy reached his equations both shear. The profound researches of de St. by the molecular hypothesis and by an Venant on the torsion of prisms and on the analysis of the oblique stress across an flexure of prisms appeared in their cominterface-methods which predicate fifteen plete form in 1855 and 1856. In both cases constants of elasticity in the most general the right sections of the stressed solids are case, reducing to but one in the case of shown to be curved and the curvature is isotropy. Cotemporaneous with Cauchy's succinctly specified; in the former Coulresults are certain independent researches omb's inadequate torsion formula is superby Lamé and Clapeyron (1828) and by seded and in the latter flexural stress is rePoisson (1829).

duced to a transverse force and a couple. Another independent and fundamental But these mere statements convey no immethod in elastics was introduced by Green pression of the magnitude of the work. (1837), who took as his point of departure Among other notable creations with a the potential energy of a conservative sys- special bearing on the theory of elasticity tem in connection with the Lagrangian there is only time to mention the invention principle of virtual displacements. This and application of curvilinear coordinates method, which has been fruitful in the by Lamé (1852); the reciprocal theorem


of Betti (1872), applied by Cerruti (1882) of perfection in the great memoir of Lato solids with a plane boundary-problems place (1805), one of the most beautiful to which Lamé and Clapeyron (1828) and examples of the Newton-Boscovichian Boussinesq (1879–85) contributed by other (1758) molecular dynamics. Capillary methods; the case of the strained sphere pressure was here shown to vary with the studied by Lamé (1854) and others; Kirch- principal radii of curvature of the exposed hoff's flexed plate (1850); Rayleigh's treat surface, in an equation involving two conment of the oscillations of systems of finite stants, one dependent on the liquid only, freedom (1873); the thermo-elastic equa- the other doubly specific for the bodies in tions of Duhamel (1838), of F. Neumann contact. Integrations for special condi(1841), of Kelvin (1878); Kelvin's analogy tions include the cases of tubes, plates, of the torsion of prisms with the supposed drops, contact angle, and similar instances. rotation of an incompressible fluid within Gauss (1829), dissatisfied with Laplace's (1878); his splendid investigations (1863) method, virtually reproduced the whole of the dynamics of elastic spheroids and the theory from a new basis, avoiding molecugeophysical applications to which they were lar forces in favor of Lagrangian displace

ments, while Poisson (1831) obtained LaFinally, the battle royal of the molecular place's equations by actually accentuating school following Navier, Poisson, Cauchy the molecular hypothesis; but his demonand championed by de St. Venant, with stration has since been discredited. Young the disciples of Green headed by Kelvin in 1805 explained capillary phenomena by and Kirchhoff — the struggle of the fifteen postulating a constant surface tension, a constants with the twenty-one constants, in method which has since been popularized other words --seems to have temporarily by Maxwell ('Heat,’ 1872). subsided with a victory for the latter With these magnificent theories prothrough the researches of Voigt (1887–89). pounded for guidance at the very threshold

of the century, one is prepared to anticiCRYSTALLOGRAPHY.

pate the wealth of experimental and of deTheoretical crystallography, approached tailed theoretical research which has been by Steno (1669), but formally founded by devoted to capillarity. Among these the Haüy (1781, "Traité,' 1801), has limited fascinating monograph of Plateau (1873), its development during the century to sys- in which the consequences of theory are tematic classifications of form. Thus the tested by the behavior both of liquid lamelthirty-two type sets of IIessel (1830) and læ and by suspended masses, Savart's of Bravais (1850) have expanded into the (1833), and particularly Rayleigh's, remore extensive point series involving 230 searches with jets (1879–83), Kelvin's riptypes due to Jordan (1868), Sohncke ples (1871), may be cited as typical. Of (1876), Federow (1890) and Schoenfliess peculiar importance, quite apart from its (1891). Physical theories of crystalline meteorological bearing, is Kelvin's deducform have scarcely been unfolded.

tion (1870) of ine interdependence of sur

face tension and vapor. pressure when varyCAPILLARITY.

ing with the curvature of a droplet. Capillarity antedated the century in little more than the provisional, though

DIFFUSION. brilliant, treatment due to Clairaut (1743). Diffusion was formally introduced into The theory arose in almost its present state physics by Graham (1850). Fick (1855),


appreciating the analogy of diffusion and elastics --- shown itself to be untrustworthy. heat conduction, placed the phenomenon It was rudely shaken when, with the rise of on a satisfactory theoretical basis, and modern electricity, the influence of the Fick's law has since been rigorously tested, medium was more and more pushed to the in particular by H. F. Weber (1879). front.'

The development of diffusion from a Another complete reconstruction of dyphysical point of view followed Pfeffer's namics is due to Thomson and Tait (1867), discovery (1877) of osmotic pressure, soon in their endeavor to gain clearness and after to be interpreted by vant' Hoff uniformity of design, by referring the (1887) in terms of Boyle's and Avogadro's whole subject logically back to Newton. laws. A molecular theory of diffusion was This great work is the first to make systhereupon given by Nernst (1887).

tematic use of the doctrine of the conservation of energy.

Finally, Hertz (1894), imbued with the In pure dynamics the nineteenth century

general trend of cotemporaneous thought, inherited from the eighteenth that un

made a powerful effort to exclude force rivaled feat of reasoning called by La

and potential energy from dynamics altogrange the ‘Mécanique Analytique' (1788),

gether-postulating a universe of concealed and the great master was present as far as

motions such as Helmholtz (1884) had 1813 to point out its resources and to watch

treated in his theory of cyclic systems, and over the legitimacy of its applications.

Kelvin had conceived in his adynamic gyroThroughout the whole century each new

static ether (1890). In fact the introducadvance has but vindicated the preeminent

tion of concealed systems and of ordered power and safety of its methods. It tri

molecular motions by Helmholtz and Boltzumphed with Maxwell (1864), when he

mann has proved most potent in justifying deduced the concealed kinetics of the electromagnetic field, and with Gibbs (1876–

the Lagrangian dynamics in its application 78), when he adapted it to the equilibrium

to the actual motions of nature. of chemical systems. It will triumph again

The specific contributions of the first in the electromagnetic dynamics of the rank which dynamics owes to the las future.

tury, engrossed as it was with the applicaNaturally there were reactions against tions of the subject, or with its mathematthe tyranny of the method of liaisons.' ical difficulties, are not numerous. In The most outspoken of these, propounded chronological order we recall naturally the under the protection of Laplace himself, statics (1804) and the rotational dynamics was the celebrated “mécanique physique' (1834) of Poinsot, all in their geometrical of Poisson (1828), an accentuation of Bos- character so surprisingly distinct from the covich's (1758) dynamics, which permeates cotemporary dynamics of Lagrange and the work of Navier, Cauchy, de St. Venant, Laplace. We further recall Gauss's prinBoussinesq, even Fresnel, Ampère and a ciple of least constraint (1829), but little host of others. Cauchy in particular spent used, though often in its applications sumuch time to reconcile the molecular perior to the method of displacement; method with the Lagrangian abstractions. Hamilton's principle of varying action But Poisson's method, though sustained by (1834) and his characteristic function such splendid genius, has, nevertheless, on (1994, 1835), the former obtainable by an more than one occasion-in capillarity, in easy transition from D'Alembert's prin

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