1881.] 



On Stratified Discharges. 



385 



cyanide muscle curve ; whilst its nervous contraction is still powerful 

 in contrast to the utter loss of excitability in the latter. 



The latency varies in the case of the different salts of ammonia. 

 Thus, in stimulating the nerve, it is much lengthened in the chloride, 

 and still more so in the cyanide — if the muscle be examined soon 

 enough to yield response to nerve stimulation — it is increased slightly 

 by ammonia, and by its nitrate and nitrite. In direct stimulation, the 

 latency appears to be increased in the cyanide nitrate and nitrite, un- 

 altered in the chloride and hydrocyanic acid, and unaltered or slightly 

 decreased in the early stages of poisoning by ammonia. 



VIII. " On Stratified Discharges. VI. Shadows of Striae." By 

 William Spotttswoode, President R.S., and J. Fletcher 

 Moulton, F.R.S. Received May 27, 1881. 



One of the most interesting questions connected with the subject 

 of stratified discharges is this : What is the physical, as distinguished 

 from the electrical, nature of the striae themselves ? Are they, in 

 fact, to be regarded as aggregations of matter possessing greater 

 density than the gas present in the dark spaces, or are they to be 

 considered as indicating merely special local electrical conditions ? 

 The fact of their having a definite configuration, especially on the 

 side which is turned towards the negative terminal of the tube, that 

 of their temperature being higher than that of the dark spaces, the 

 manner in which they are affected by solid bodies, and other considera- 

 tions, all tend to give support to the view that the striae are loci of 

 greater density than the dark spaces. Still it can hardly be said that 

 as yet any experimental proof of this has been given, sufficiently 

 decisive to decide the question conclusively. And it is in the hope of 

 contributing something towards the solution of this question that 

 the following experiments are submitted to the notice of the Royal 

 Society. 



In the former papers of this series (" Proc. Roy. Soc," vols. 23, 27), 

 and in our memoirs " On the Sensitive State of Vacuum Discharges " 

 ("Phil. Trans.," 1879, p. 155, and 1880, p. 561), we have described 

 experiments which show how a discharge through a tube, whether 

 sensitive or non -sensitive, may be affected in various ways by inter- 

 mittent discharges ab extra. In the experiments now to be described 

 the problem has been reversed, and it has been proposed to ascertain 

 how far such an external discharge can itself be affected by the 

 internal one. The discharge ab extra, however, presents such feeble 

 luminosity, that it is not possible to come to any certain conclusions 

 on this head by direct methods. But, as has been before pointed out, 



