CONTRIBUTIONS TO SCIENCE. 



533 



To account for the transmission of rotation in the same 

 direction from one molecular vortex to the next, Maxwell 



Fig. 10. 



supposed that there exists between them a number of ex- 

 tremely minute spherical bodies which roll, without sliding, 

 in contact with the surfaces of the vortices. These bodies 

 serve the same purpose as "idle wheels" in machinery, 

 which, coming between a driver and follower, transmit the 

 motion of the former to the latter unchanged in direction. 

 These minute spherical particles Maxwell supposed to con- 

 stitute electricity. They roll upon the cells or vortices as 

 if the surfaces in contact were perfectly rough, or provided 

 with teeth gearing into one another, and thus, whatever 

 forces may be applied, sliding is impossible. What we 

 ordinarily consider as molecules of matter are supposed to 

 be very large compared with the molecular vortices, and 

 therefore d fortiori with the particles of electricity. In an 

 insulator, or dielectric, it is supposed that the electric par- 



