No. ♦).] president's address b. a. a. s. 357 



of electrical discharire his study for several years, and resorted 

 in his important experiments to a special source of electric power. 

 In a note addressed to me, Dr. Spottiswoode describes the nature 

 of his investigations n>uch more clearly than I could venture to 

 give them. He says : " It had long been my opinion that the 

 dissymmetry shown in electrical discharges through rarified gases 

 must be an essential element of every disruptive discharge, and 

 that the phenomena of stratification might be regarded as magni- 

 fied imau'cs of features always present, but concealed under or- 

 dinary circunstances." It was with a view to the study of this 

 question that the researches by Moulton and myself were under- 

 taken. The method chiefly used consisted in introducing into 

 the circuit intermitteuce of a particular kind, whereby one lumi- 

 nous discharge was rendered sensitive to the approach of a con- 

 ductor outside the tube. The application of this method enabled 

 us to produce artificially a variety of phenomena, including that 

 of stratification. We were thus led to a series of conclusions 

 relatino- to the mechanism of the dischar^'e, amonsi; which the 

 following may be mentioned : 



''1. That a stria, with its attendmt dark space, forms a phys- 

 ical unit of a striated discharge. 



2. That the oriain of the luminous column is to be souirht for 

 at its negative end ; that the luminosity is an expression of a 

 demand for negative electricity. 



3. That the time occupied by electricity of either name in 

 traversing a tube is greater than that occupied in traversing an 

 equal length of wire, but less than that occupied by molecular 

 streams (Crooke's radiations) in traversing the tubes. 



4. That the brilliancy of the light with so little heat may be 

 due in p.irt to brevity in the duration of the discharge. 



5. Til at striae are not merely loci in which electrical is con- 

 verted into luminous eneriry, but are actual aooreo;ations of 

 matter. 



This last conclusion was based mainly on experiments made 

 with an induction coil excited in a new way, — viz., directly by 

 an alternating machine, without the intervention of a commuta- 

 tor or condenser. This mode of excitement promises to be one 

 of great importance in spectroscopic work, as well as in the study 

 of the discharge in a magnetic field, partly on account of the 

 simplification which it permits in the construction of induction 

 coils, but mainly on account of the very great increase of 

 strength in the .secondary currents to which it gives rise." 



