ADDRESS. 31 



experiments to a special source of electric power. In a note addressed 

 to me, Dr. Spottiswoode describes the nature of Lis investigations much 

 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 rarefied gases, must be an essential element of every disruptive 

 discharge, and that the phenomena of stratification might be regarded 

 as magnified images of features always present, but concealed under 

 ordinary circumstances. It was with a view to the study of this ques- 

 tion that the researches by Moulton and myself were undertaken. The 

 method chiefly used consisted in introducing into the circuit intermittence 

 of a particular kind, whereby one luminous discharge was rendered 

 sensitive to the approach of a conductor outside the tube. The applica- 

 tion of this method enabled us to produce artificially a variety of pheno- 

 mena, including that of stratification. We were thus led to a series of 

 conclusions relating to the mechanism of the discharge, among which 

 the following may be mentioned : — 



' 1. That a stria, with its attendant dark space, forms a physical unit 

 of a striated discharge ; that a striated column is an aggregate of such 

 units formed by means of a step-by-step j^rocess ; and that the negative 

 glow is merely a localised stria, modified by local circumstances. 



' 2. That the origin of the luminous column is to be sought for at its 

 negative end ; that the luminosity is an expression of a demand for 

 negative electricity ; and that the dark spaces are those regions where 

 the negative terminal, whether metallic or gaseous, is capable of exerting 

 sufficient influence to prevent such demand. 



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

 tube is greater than that occupied in traversing an equal length of wire, 

 but less than that occupied by molecular streams (Crookes' radiations) in 

 traversing the tubes. Also that, especially in high vacua, the discharge 

 from the negative terminal exhibits a durational character not found at 

 the positive. 



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

 part to brevity in the duration of the discharge ; and that for action so 

 rapid as that of individual discharges, the mobility of the medium may 

 count as nothing ; and that for these infinitesimal iieriods of time gas 

 may itself be as rigid and as brittle as glass. 



' 5. That strise are not merely loci in which electrical is converted into 

 luminous energy, but are actual aggregations of matter. 



' This last conclusion was based mainly upon experiments made with 

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

 machine, without the intervention of a commutator or condenser. This 

 mode of excitement promises to be one of great importance in spectro- 

 scopic 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.' 



