144 Royal Society: — 



a book such as the present, it was 110 part of the author's duty to 

 refute objectionable doctrines. He does not, for instance, refute the 

 doctrine of Metempsychosis ; he merely states what it was : and in 

 like manner he lets Polytheism pass with nothing more than defi- 

 nition. 



We had marked some other passages for comment ; but our limits 

 are reached, and we will only add that our criticisms are not in- 

 tended to show more than that, where much has been well doue, 

 something might have been done better. 



XXIT. Proceedings of Lemoned Societies. 



ROYAL SOCIETY. 



[Continued from p. 73.] 



May 18, 1876.— Dr. J. Dalfcon Hooker, C.B., President, in the Chair. 



HE following communication was read 



T 



J - " On Stratified Discharges. — II. Observations with a Revol- 

 ving Mirror." By William Spottiswoode, M.A., Treas. R.S. 



In a paper published in Poggendorff's 'Annalen,' Jubelband, 

 p. 32, A. "Wiillner has described a series of observations made, by 

 means of a revolving mirror, upon the discharge of a large in- 

 duction-coil through tubes containing ordinary atmospheric air at 

 various degrees of pressure. When, as is generally the case with 

 an induction-spark, the discharge occupies an appreciable interval 

 of time, the image in the mirror appears spread out to a breadth 

 proportional to the duration and to the velocity of rotation. The 

 successive phases of the phenomena then appear, as usual, arranged 

 in successive positions, and may be studied separately, even when 

 too rapid to be disentangled by the unassisted eye. 



Wiillner's observations appear to have been directed rather to 

 the nature of the coil-discharge than to that of the stratifications ; 

 and some of his principal conclusions are accordingly of the fol- 

 lowing kind, viz. that at low pressures, i. e. down to 1 millim., 

 w T hen the discharge was stratified, the striae showed an inter- 

 mittence of intensity, indicating either a pulsation within the 

 duration of the main discharge or a breaking-up of the main 

 into a series of partial discharges. At greater pressures, e. </. 

 at 26 millims., when almost all trace of stratification was lost, this 

 breaking-up into partial discharges (especially at the commence- 

 ment) was distinctly perceptible. At yet greater pressures, i. e. 

 from 40 millims. to 75 millims., a cloudy kind of stratification 

 showed itself; but, excepting a bright flash at the outset, no 

 appearance of partial discharge was visible. The observations, 

 which were at first directed to capillary tubes, were extended to 

 tubes of various diameters, and also included the effect of a mag- 

 net on the discharge. 



For some time prior to the publication of the volume in question 

 I had been engaged upon a series of experiments very similar 

 in their general disposition, but with a somewhat different object 



