io8 THE LIMITATIONS OF SCIENCE 



ment of Faraday's lines of force. Faraday believed 

 that when a body is electrified the space about it is 

 filled with lines of electric force which are stretched in 

 the direction of their length and experience a pressure 

 at right angles to their direction. This idea, or rather 

 the modification of it by Maxwell, who was able to as- 

 sign quantitative values to those forces which corre- 

 spond with the laws of electrical attraction and repul- 

 sion, is expressed more precisely. But qualitatively: 

 that is, in telling us what electricity is ; why it is pro- 

 duced by friction; and what lines of force are; the 

 modern statement is no more definite than that of Des- 

 cartes. It is a mistake, however, to suppose he pos- 

 sessed a unique power of formulating hypothesis ; other 

 early writers attained eminence in this respect. Thus 

 Sir Thomas Browne thought that electric effluvia (the 

 prevailing name for force) behave like threads of 

 syrup which elongate and contract and so produce at- 

 traction; Von Guericke stated that bodies contain efflu- 

 via which emanate from them according to their nature 

 and form an electric field of force. In agreement with 

 these opinions, we are taught to-day that the best way 

 to consider lines of force is to picture an electrified 

 body as one surrounded by stretched elastic bands. As 

 a diagram to show the direction of motion of an at- 

 tracted body, and as a name for the quantity of force, 

 this conception of elastic lines of force is accurate and 

 convenient. But Faraday and Maxwell went far be- 



