1877.] Photographic Image of Stratified Discharges. 323 



tive phenomena of the gastrocnemius muscle, as based on the researches 

 I have just referred to, will find it succinctly given in an admirable little 

 work just published by Prof. Rosenthal, in the " International Scientific 

 Series" (' Allgemeine Physiologie der Muskel und jNerven'), pp. 195-197. 

 He will thereby be able to satisfy himself that that explanation covers 

 mauy of the facts to which I directed attention in my " Koto." 



I am, my dear Sir, 



Tours faithfully, 



J. B. Sandekson. 



Prof. Huxley, Sec, E.S. 



VII. " Photographic Image of Stratified Discharges/-' A Letter 

 to Prof. Stokes, Sec. R.S._, by W. Spottiswoode, M.A., 

 Treas. R.S. Received June 2, 1877. 



41 Grosvenor Place, 

 June 2, 1877. 



My Deak Stokes, — I am sure that you will be interested to hear that 

 Capt. Abney yesterday succeeded in photographing some of the pheno- 

 mena which I had observed last year with a revolving mirror, and which 

 are described in my paper " On Stratified Discharges, III." (Proceedings 

 of the Ro}^al Society, vol. xxv. p. 73). The success of the operation was 

 due mainly to his skill, but partly also to the great brilliancy and long 

 duration of the discharges from my large induction-coil, described in the 

 ' Phil. Mag.' for February last. 



The tube used on this occasion was a small hydrogen-tube of conical 

 form, the effect of which, as seen in a revolving mirror, is represented in 

 fig. 3 of the paper above quoted. The photographic image was obtained, 

 not by the use of a mirror, but by moving the sensitive plate across the 

 field of view during the continuance of the discharge. In this the first 

 result, the position of the stria), their proper motion, their grouping in 

 pairs of different actinic power, and consequently of colour (a phenomenon 

 well known in hydrogen tubes), are distinctly developed. Other features, 

 of which I reserve the description, are also noticeable. 



I hope on some future occasion to make a fuller communication upon 

 the subject to the Royal Society ; but in the mean time, if you think the 

 matter of sufficient interest, I shall be much obliged by your offering this 

 as a Preliminary Note. 



Believe me, 



Tours very sincerely, 



"W. Spottiswoode. 



