CONTENTS. 



CHAPTEK I. 



y THE THEORY OF THE AETHER IN THE SEVENTEENTH CENTURY. 



Page 



Matter and aether, . . . . . . .1 



The physical writings of Descartes, ..... 2 



Early history of magnetism : Petrus Peregrinus, Gilbert, Descartes, 7 

 Fermat attacks Descartes' theory of light : the principle of least 



time, ........ 10 



Hooke's undulat>ry theory : the advance of wave -fronts, . . 11 



Newton overthrows Hooke's theory of colours, . . .15 



Conception of the aether in the writings of Newton, . . 17 



Newton's theories of the periodicity of homogeneous light, and of 



fits of easy transmission, . . ,20 



The velocity of light : Galileo, Roemer, . . . .21 



Huygens' Traite de la lumiere : his theories of the propagation of 



waves, and of crystalline optics, . . .22 



Newton shows that rays obtained by double refraction have sides : 



his objections to the undulatory theory, . . .28 



X 



CHAPTER II. 



ELECTRIC AND MAGNETIC SCIENCE, PRIOR TO THE INTRODUCTION OF 

 THE POTENTIALS. 



The electrical researches of Gilbert : the theory of emanations, . 29 

 State of physical science in the first half of the eighteenth century, 32 

 Gray discovers electric conduction : Desaguliers, . . 37 



The electric fluid, ....... 38 



Du Fay distinguishes vitreous and resinous electricity, . .39 



Xollet's effluent and affluent streams, . . . .40 



The Leyden phial, ..... . . 41 



The one-fluid theory : ideas of Watson and Franklin, . . 42 



Final overthrow by Aepinus of the doctrine of effluvia, . . 48 



Priestley discovers the law of electrostatic force, . . .50 



