22 ANNUAL OF SCIENTIFIC DISCOVERY. 



historian of Natural Science, has remarked, that " future discoveries may 

 make gravitation a case of some wider law, and may disclose something of 

 the mode in which it operates." The difficulty, indeed, of conceiving a 

 force acting through nothing from body to body, has of late made itself felt ; 

 and more especially since Meyer of Heilbronn first clearly expressed the 

 principle of the " conservation of force." Newton, though apprehending 

 the necessity of a medium by which the force of gravitation should be con- 

 veyed from one body to another, yet appears not to have possessed such an 

 idea of the uncreateability and indestructibility of force as that which, now 

 possessed by minds of the highest order, seems to some of them to be in- 

 compatible with the terms in which Newton enunciated his great law, viz., 

 of matter attracting- matter with a force which varies inversely as the 

 square of the distance. The progress of knowledge of another form 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 disco very of Jupiter's satellites supplied Romerwith the phenomena 

 whence he was able to measure, in 1676, the velocity of light. Descartes, in 

 his theory of the rainbow, referred the different colors to the different amount 

 of refraction, and made a near approximation to Newton's capital discovery 

 of the different colors entering into the composition of the luminous ray, 

 and of their different refrangibility. 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 undula- 

 tions or vibrations of an ether would explain certain phenomena, adopted 

 the hypothesis of emission as most convenient for the mathematical propo- 

 sitions relative to light. The discoveries of achromatism, of the laws of 

 double refraction, of polarization circular and elliptical, and of dipolariza- 

 tion, rapidly followed: the latter advances of optics, realizing more than 

 Bacon conceived might flow from the labors of the " Perspective House," 

 are associated with and have shed lustre on the names of Dollond, Young, 

 Mains, Fresnel, Biot, Arago, 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 alchemy : Geology and Palaeontology 

 were undreamt of: but Magnetism and Electricity had begun 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 Magnate," 

 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 trackless seas. Gilbert, to whom the name " electricity " is due, 

 observed that 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 bj r 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 vicinit} r of the electric body." The conduction of electric force, and the 

 different behavior of bodies in contact with the electric, leading to their 

 division, by Desaguliers, into conductors and non-conductors, next followed. 

 The two kinds of electricity, at first by Dufay, their definer, called "vitre- 

 ous " and " resinous," afterwards, by Franklin, " positive " and " negative/' 



