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Mr. J. Joly. 



discharge was taken, resting the glass on a conductor. It is to be 

 observed, in the first place, that the figures obtained on this surface do 

 not generally penetrate to the glass, but are impressed on the surface 

 of the sublimate. At the same time, the grain is exceedingly fine, 

 bearing examination with a high power under the microscope. Taken 

 on ordinary glass (such as is used in photography), the negative 

 exhibits a centre of fine bent veins and a faint bat very beautiful, 

 irregular halo, with wavy border, extending in the direction of the 

 positive pole. The positive most resembles the outspread tentacles of 

 some of the larger sea anemones (fig. 1), but the tentacles, magnified, 

 are seen to have the curious structure sketched in fig. 2. Their extreme 



Fig. 2. 



Enlargement of tentacles. 



points are deeply sunken in the powder, and they sometimes bifurcate 

 at the extremity and curl round, meeting each other in a very peculiar 

 way. Each contains a central core of undisturbed material ; they are, 

 in fact, outlined only. On thin glass very delicate figures are obtained. 

 The positive somewhat resembles Mr. Brown's photographs for that 

 pole — veins bordered with innumerable streaming lines. The nega- 

 tive shows a strong resemblance to the positive, being, in fact, a 

 similar pattern with finer streamers. In this last case again we might 

 suppose that the discharge was shared to a greater extent by the 

 sublimate, and differences between the positive and negative gas dis- 

 charges accordingly reduced. 



The undisturbed core in the spark lines has been observed in the 

 case of spark tracks over smoked glass (Topler). It is developed in 

 breath- figures, or is seen when sparks from a Holtz machine, or from 



