150 Royal Society: — 



Fig. 4 represents a chloroform-tube, in which a piece of cotton- 

 wool had been inserted with the view of ascertaining whether any 



Tiff. 4. 



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motion would be communicated to it by the current. This proved 

 to be the case ; but I do not attempt here to describe the phe- 

 nomenon. To the unassisted eye the discharge was extremely 

 brilliant; it passed in a column not quite straight, but in a 

 writhing snake-like curve, with flaky striae at intervals through 

 its length. When viewed in the mirror the striae were seen to 

 spread themselves out with slight, but irregular, proper motion. 

 "With an increased battery-surface, or with a greater number of 

 cells, but more notably with the latter, not only were the striae 

 lengthened, but from several of the long elementary striae shorter 

 ones were thrown out nearly at right angles to the former. These 

 were of short duration, and had great proper motion. The general 

 appearance of these compound striae was that of branches of fir 

 trees, the twigs of which represented the permanent striae, and the 

 leaves the secondary. 



Beside these, a large (Geissler's " hydrocarbon ") tube was exa- 

 mined with a magnet the pole of which was placed near the 

 head of the column ; and in order to trace more in detail the effect 

 of the magnet, its strength was varied by raising or lowering the 

 battery-plates. The general character of the discharge without 

 the magnet was very similar to that represented in fig. 1. On 

 slightly lowering the plates of the magnet-battery the discharge 

 spread itself over a greater breadth than before. At the same 

 time the elementary striae, which had for the most part been con- 

 tinuous, were now broken up into short lengths, presenting the 

 first features of flocculent striae. On further lowering the plates 

 these flocculent striae became more and more developed until the 

 whole field in the neighbourhood of the magnetic pole became filled 

 with such striae. It is well known that one effect of the mag- 

 netic field is to bring out striae in portions of tubes where no striae 



