.")•_' Trowbridge — New Emission Theory of Light. 



tied together. Can we blame the metaphysicians for smiling, 

 and saving " Von physicists are coming into our ranks"? But 

 are we not supplanting the hypothesis of a fluid which Alls all 

 space, a fluid which is thinner than any gas, a something which 

 has do resemblance to anything of which we have cognizance 

 and which is .more elastic than steel, by another fantastic 

 hypothesis i We have, however, given up the fluid theories 

 in electricity and instead of media we have motions of elec- 

 trons. Light is an electro-dynamic phenomenon, and the 

 hypothesis I frame extends the motion of electrons from the 

 confines of electrical circuits to the extent of space. 



I have said that we have abandoned the fluid theories of 

 electricity. This is true of the two fluid theories ; but we see 

 some merits still in Benjamin Franklin's one fluid theory, in 

 the light of the electron theory. Franklin accounted for 

 attraction and repulsion by an excess or diminution of a fluid. 

 His theory could become an electron theory if instead of an 

 excess or deficit of a fiuid we read excess or deficit of negative 

 electrons. The attachment or detachment of the negative 

 electrons explain in a plausible manner the fundamental 

 experiment of the attraction or repulsion of electrified pith- 

 balls. Can we extend the modified Franklin theory to account 

 for magnetism and diamagnetism ? We should be able to do 

 this, for as Maxwell remarks : " Every phenomenon in electro- 

 statics has its analogy in magnetism." 



To answer this question I am led to the subject of canal 

 rays, which has greatly interested me ;* for in this phenome- 

 non we are brought into close consideration of what is perhaps 

 the most important question in the theory of electricity : 

 " What is positive electricity ?" 



The negative electron has been identified in the discharge 

 from the negative cathode in Geissler tubes and the positive 

 rays proceeding from orifices in the cathode — the so-called 

 canal rays — are supposed to be a phenomenon of the positive 

 electrons. To account for the positive rays we have a multi- 

 tude of theories of combination and neutralization of single 

 entities and doublets. From the cathode in a Geissler tube, at a 

 suitable exhaustion, proceed negative electrons from every unit 

 of surface both toward the positive terminal of the tube and 

 toward or into the region where the canal rays manifest them- 

 selves, that is away from the positive terminal and back of the 

 cathode. The canal rays appear to emanate from the canals 

 or perforations in the cathode, and also proceed in both direc- 

 tions, one toward the positive terminal and the other in the 

 direction away from the terminal. 



*Proe. Am. Acad., xlv, No. 19. Ibid., xliii, No. 20. 



