530 Dr. J. H. Vincent : Electrical Experiments 



dynamo. The striations are due to oscillations in a circuit 

 consisting of the lamp with coils and condensers arranged in 

 series, the coils and condensers being in parallel with the 

 lamp. The experiment is a variation of those of Duddell on 

 the singing arc. The calculated frequency of the oscillations 

 in this circuit, neo-lectino- resistance, was 950. The effective 

 resistance of the arc was found to be 860 ohms, the other 

 resistance in the oscillatory circuit being 120 ohms ; allowing 

 for this total resistance of 980 ohms, the corrected frequency 

 becomes 864. By measuring the photograph, the observed 

 frequency is 869. 



Striations can also be obtained by similar methods when a 

 lamp is giving the fan effect. Increasing the self-induction 

 or the capacity lengthened the period. 



Attempts to obtain photographs of a striated necklace by 

 this method have been unsuccessful, the disturbance produced 

 by the shunt-circuit being great enough to cause the necklace 

 to break. 



The Green Glow. 



This was first noticed in connexion with this research when 

 experimenting on the ribbon effect. It was found that when 

 the current was switched off while the lamp was giving a 

 steady arc between the ends of the broken mercury columns, 

 under reduced hydrostatic pressure, the light did not go out 

 at once, but lingered feebly between the two columns. As 

 the tube cools in a second or two, the columns have approached 

 within a couple of millimetres or so, and then this glow dies 

 out ; the ends of the column then approach steadily until 

 they join. 



This light, when produced in fused quartz lamps from which 

 the current has just been switched off, looks grass-green in 

 colour, in contrast, to the bluish-white light deficient in red 

 to which the eye has just been exposed. In contrast, how- 

 ever, with daylight it is of a greenish-blue tint. 



In most cases when the current is switched on again while 

 the green glow continues, the lamp relights. Sometimes the 

 main luminosity of the lamp when giving the ribbon effect 

 on a high voltage (400) suddenly ceases. In short tubes the 

 green glow then appears, and may be replaced as long as 

 eight seconds later, by the lamp lighting again automatically, 

 without the columns having come into contact. 



The green glow is not caused by the external electromotive 

 force applied to the tube, nor does it necessarily depend 

 for its formation upon the vapour having previously been 



