18 jMr. W. R. Grove mi the Strice seen in 



Substituting for W, integrating, substituting to form BY and BS, 

 and determining the constants of integration to satisfy the pri- 

 mary equation and the condition that 6S = when a; = 0, we find 

 at length, 



SY=.x{-|(e7-e-7) + (g + |){6^-ei-|(e'+e-'? + 2)}, 



G. B. Airy. 



II. On the Stria seen in the Electrical Discharge in vacuo. 

 Bi/ W. R. Grove, V.P.R.S. ^c. 



IN a paper communicated to the Royal Society in January 1 852, 

 I published the first notice of transverse bands or striae which 

 are seen in the discharge from a Ruhmkorfi" coil in the vacmim 

 of an air-pump, wherein is placed a piece of phosphorus ; and in 

 a postscript to that paper (Phil. Mag. vol. iv.) I stated that the 

 striae could be seen in several attenuated gases, probably in all. 

 Some time after the publication of my paper, but without 

 having seen it, M. Ruhmkorff observed the same phaenomenon 

 in the vapour of alcohol ; and it has subsequently been experi- 

 mented on by Messrs. Masson, Quet, Du Moncel, Robinson, and 

 Gassiot, the last of whom has elaborately examined it in the 

 Torricellian vacuum. 



No satisfactory rationale of the phaenomenon has been given. 

 In my first paper I gave no opinion as to its cause ; but subse- 

 quently, in a communication to the British Association at Hull, 

 I stated my belief that it was closely connected with the inter- 

 ruptions of the contact breaker. The following is the notice of 

 my communication in the Athenaeum, August 30, 1856: — "Mr, 

 Grove has observed that the mode of breaking contact has a 

 marked influence on the phaenomenon. If, for instance, the arm 

 of the contact breaker be made to rest on a slight spring placed 

 underneath it, the bands become narrower. If a single breach 

 of contact be effected, most observers have remarked that the 

 effect is still perceptible: but it is very difficult to effect a single 

 breach of contact ; the fusion of the metals at the point of con- 

 tact with the vibration accompanying the movement, occasions 

 a double or triple disruption. The best mode is to place two 

 stout copper wires across each other, and with a firm hand draw 



* Communicated by the Author. 



