6"6 BRITISH ASSOCIATION TOR 



and indestructibility of force as tliat which, now possessed by minds of the highest 

 order, seems to some of them to be incompatible with the terms in which Newton 

 enunciated his great law, viz , of matter attracting matter with a force which va- 

 ries inversely as the square of the distance. The progress of knowledge of an- 

 other form of all-pervading force, which we call, from its most notable effect on one 

 of tiie senses, " Light," has not been less remarkable than that of gravitation. Ga- 

 lileo's discovery of Jupiter's satellites supplied Romerwlth the phenomena whence 

 be was able to measure, in 1676, 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 refrangi- 

 bility. 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, propa- 

 gated from the luminous point spherically, like those of sound, i'^ ewton, whilst 

 admitting that such undulations or vibrations of an ether would explaiu certuin 

 phenomena, adopted the hypothesis of emission as most convenient for the mathe- 

 matical 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 concei- 

 ved might flow from the labours of the " Perspective House," are associated with 

 and have shed lustre on the names of DoUond, Young, Mai us, Fresnel, Biot, xirago, 

 Brewster, Stokes, Jamin, and others. Some of the natural sciences, as we now 

 comprehend them, had not germinated in Bacon's time. Chemistry was then alche- 

 my; Geology and Palseontology were undreamt of: but Magnetism and Electri- . 

 city had began to be observed, and their phenomena compared, and defined, by a 

 contemporary of Bacon in a way that claims to be regarded as the first step towards 

 a scientific knowledge of those powers. It is true that, before Gilbert, ('De Ma- 

 gnete,' 1600), the magnet was known to attract iron, and the great practical appli- 

 cation 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 track- 

 less seas. Gilbert, to whom the name "electricity" is due, observed ihat that force 

 attracted light bodies, whereas the magnetic force attracted iron only. About a 

 century later the phenomena of repulsion as well as of attraction of light bodies by 

 electric substances were noticed: and Dufay,in 1733, enunciated the principle, that 

 " electric bodies attract all those that are not so, and repel them as soon as they 

 are become electric by the vicinity of the electric body" The conduction of elec- 

 tric force, and the different behaviour of bodies in contact with the electric, leading 

 to their division, by Desguliers, into conductors and non-conductors, next followed. 

 The two kinds of electricity, at first by Dufay, their definer. called " vitreous " and, 

 "resinous," — afterwards, by Franklin, "positive" and "negative," formed an im- 

 portant step, which led to a brilliant series of experiments and discoveries, with 

 nventions, such as the Leyden jar, for intensifying the electric shock. The disco- 

 very of the instantaneous transmission of electricity through an extent of not les3 

 than 12,000 feet, by Bishop Watson, together with that of the electric state of the 

 clouds, and of the power of drawing off such electricity by pointed bodies, as shown 

 by Franklin, was a brilliant beginning of the application of this science to the well- 



