Professor Owen's Address. 37*7 



other from of all-pervading force, which we call, from its most 

 notable effect on one of the senses, " Light," has not been less 

 remarkable than that of gravitation. Galileo's discovery of 

 Jupiter's satellites supplied Romer with the phenomena whence he 

 was able to measure, in 16*76, the velocity of light. Descartes, in 

 his theory of the rainbow, referred the different colours to the 

 different amount of refraction, and made a near approximation to 

 Newton's capital discovery of the different colours entering into 

 the composition of the luminous ray, and of their different refran- 

 gibility. Hook and Huyghens, about the same period, had entered 

 upon explanations of the phenomena of light conceived as due to 

 the undulations of an ether, propagated from the luminous point 

 spherically, like those of sound. Newton, whilst admitting that 

 such undulations or vibrations of an ether would explain certain 

 phenomena, adopted the hypothesis of emission as most convenient 

 for the mathematical propositions relative to light. The discoveries 

 of achromatism, of the laws of double refraction, of polarization 

 circular and elliptical, and of dipolarization, rapidly followed : the 

 latter advances of optics, realizing more than Bacon conceived 

 might flow from the labours of the " Perspective House," are as- 

 sociated with and have shed lustre on the names of Dollond, 

 Young, Mains, Fresnel, Biot, Arago, Brewster, Stokes, Jamain, and 

 others. 



MAGNETISM AND ELECTRICITY. 



Some of the natural sciences, as we now comprehend them, had 

 not germinated in Bacon's time. Chemistry was then alchemy ; 

 Geology and Palseontology were undreamtof: but Magnetism and 

 Electricity had begun to be observed, and their phenomena com- 

 pared, and defined, by a contemporary of Bacon, in a way that 

 claims to be regarded as the first step towards a scientific know- 

 ledge of those powers. It is true that, before Gilbert (' De 

 Magnete,' 1600), the magnet was known to attract iron, and the 

 great practical application of magnetized iron — the mariner's 

 compass — had been invented, and for many years before Bacon's 

 time had guided the barks of navigators through trackless seas. 

 Gilbert, to whom the name " electricity" is due, observed that 

 that force attracted light bodies, whereas the magnetic force 

 iron only. About a century later the phenomena of repul- 

 sion as well as of attraction of light bodies by electric subs- 

 tances were noticed : and Dufay, in 1733, enunciated the 



