LIESEGANG S LINES. 313 



One is forcibly reminded of the circular magnetic field surround- 

 ing a wire conveying a current, and the action of one set of lines 

 upon another set suggests the effect seen, when a number of wires 

 conveying currents in the same direction are placed somewhat 

 close together and iron filings scattered round them in a plane at 

 right angles to the direction of the current. In fact, it seemed 

 that any of the combinations of lines might be reproduced by the 

 action of currents on iron filings. 



Another method of obtaining the lines was devised. This con- 

 sisted in boring a hole through a glass plate and passing a fine 

 silver wire through it. The gelatin was poured upon the plate and 

 a ring of ilver wire arranged round it, so that a current could be 

 passed thus from the wire to the ring. The central wire was made 

 the anode of a battery of two storage cells. The current, passing 

 through the gelatin radially, gave rise to a similar set of lines owing 

 to the solution of the silver. No distortion occurred, and the growth 

 went on as regularly as was the case with a speck of silver nitrate, 

 the manner of growth of the rings being uninfluenced by the flow 

 of the current. If a number of wires were arranged as anodes, the 

 same combination figures were obtained as was the case with a 

 number of specks of silver nitrate. 



The lines were made to grow in magnetic and electrostatic fields, 

 but no distortion occurred. Even when an electrostatic field of 

 1,000 volts was applied, by a pair of platinum plates embedded in 

 the gelatin, no effect upon the manner of growth was observed. 



The figures were photographed under a magniiication of 30 

 diameters. 



As might be expected from the law of the radius of the rings 

 the system acts as a "zone" plate, and images of the objects 

 placed in front can be cast upon a screen in exactly the same 

 manner as those formed by ordinary zone plates. 



TREE VEGETATION OF THE NORTH = EASTERN 

 TRANSVAAL. — The Transvaal Conservator of iForests, 

 Mr. C. E. Legat, made a journey, some little while ago, from 

 Pietersburg, across the Zoutpansberg" Range, for the purpose 

 Oi studying the trees in the extreme north-east of the Trans- 

 vaal — a region in which comparatively little botanical collection 

 has been done. In a recent number of the Kew Bulletin Mr. 

 Legat gives an account of his trip : South of the Zoutpansberg- 

 Range he found Dombeya rotundifolia, Sclerocarya caffra, 

 Dichrostachys nutans, and Acacia horrida, and north of the 

 range he met with Copaifcra mopanc, Ptcrocarpiis angolcnsis. 

 and Adansonia digitata. In some localities Black Stinkwood 

 (Ocotca hnllata) was fairly common, and at Spelonken large 

 trees of Trichilia cmctica (Red Essenwood) and Eckcbcrgia 

 Mcycri (Essenwood) were observed and photographed. 



