418 



SCIENCE. 



[N. S. Vol. XX. No. 509. 



posed to limit the wide range of inclusion 

 specified by our program, Ave must at once 

 disclaim any attempt to speak authorita- 

 tively vyitli respect to most of its details. 

 There is, in fact, such a vast array of 

 knowledge now comprehended under any 

 one of the six departments of our division, 

 that the boldest author must hesitate to 

 enter on a limited discussion with respect 

 to any of them. But if it is thus difficult 

 to consider any department of physical 

 science, it appears incomparably more diffi- 

 cult to contemplate all of them in the be- 

 wildering complexity of their interrela- 

 tions and in the bewildering diversity of 

 their subject-matter. Wliat, for example, 

 could seem more appalling to the average 

 man of science than the duty of explaining 

 the connections of archeology and astro- 

 physics or those of ecology and electrons? 



Happily, however, the managers of the 

 congress have provided an adequate divi- 

 sion of labor, whereby the technical details 

 of the various departments are allotted to 

 experts, giving thus to a divisional speaker 

 a degree of freedom with respect to depth in 

 some way commensurate with the breadth 

 of his task. Presuming, therefore, that I 

 may deal only with the broader outlines 

 and salient features of the subject, I invite 

 your attention to a summary view of the 

 present status and the apparent trend of 

 physical science. 



Whatever may be affirmed with respect 

 to science in general, there appears to be no 

 doubt that all of the physical sciences are 

 characterized by three remarkable unities 

 — a unity of origin, a unity of growth and 

 a imity of purpose. Physical science orig- 

 inates in observation and experiment; it 

 rises from the fact-gathering stage of un- 

 related qualities to the higher plane of re- 

 lated quantities, and passes thence on to 

 the realm of correlation, computation and 

 prediction under theoiy; and its purpose 

 is to interpret in consistent and verifiable 



temis the universe, of which Ave form a 

 part. The recognition of these unities is 

 of prime importance; for it helps us to 

 understand and to anticipate a great di- 

 versity of perfection amongst the different 

 branches of science, and hence leads us to 

 appreciate the desirability of hearty co- 

 operation on the part of scientific workers 

 in order that progress may be ever positive 

 towards the common goal. 



Glancing rapidly seriatim at the differ- 

 ent departments of physical science as 

 specified by our program, Ave come first to 

 a consideration of formal physics, and we 

 may most quickly orient ourselves aright 

 in this department by trying to state in 

 what respects the physics of to-day differs 

 from the physics of a hundred years ago. 



In spite of the extraordinary perfection 

 of the work of Lagrange, Laplace, Fourier, 

 Young, Fresnel, Poisson, Green, Gauss and 

 others of the early part of the nineteenth 

 century, it will be at once admitted that 

 great progress has been made. In addition 

 to noteworthy advances and improvements 

 along the lines laid doAvn by these masters, 

 there have been developed the relatively 

 new fields of elasticity, electromagnetics, 

 thermodynamics and astrophysics ; and 

 there has been discovered the widest of all 

 generalizations in physical science — the law 

 of conservation of energy. "Whereas it was 

 easy a century ago to conceive, as in gravi- 

 tational astronomy, of action at a distance 

 across empty space, the univ^erse in the 

 meantime has come to appear more and 

 more plethoric not only with ' gross matter, ' 

 but Avith that most Avonderf ul entity Ave call 

 the ether. The astronomers have shown 

 us, in fact, that the number of molar sys- 

 tems in the universe is enormously greater 

 than was supposed possible a century ago ; 

 Avhile the physicists have revealed to us 

 molecular systems riA^aling our solar sys- 

 tem and its JoA'ian and Saturnian subsys- 

 tems, and theA' have loaded doAvn the ether 



