Liquid Coherers and Mobile Conductors. 375 



electrodes. In order to retard the spontaneous coherence of 

 the mercury, resulting from mutual pressure of the spheroids, 

 it is well to keep the tube horizontal. If, however, it is 

 desired quickly to convert a body of mercury from the sub- 

 divided to the ordinary state, sparks may be passed into the 

 tube w T hile it is more or less vertical. The running-together 

 of subdivided mercury is more leisurely to be observed with 

 large globules. These form separate, elongated, conductors. 

 The way in which they unite will be referred to in describing 

 Experiment 3. 



Experiment 2. — A glass tube, similar to the first, but some- 

 what wider, is nearly filled with a mixture of paraffin-oil and 

 water, and vigorously shaken. I propose to call this a " rain " 

 tube. If it is kept at rest, the oil, in the common course of 

 events, floats to the top in a few minutes. The " rain " tube, 

 however, shows that the separation, especially towards the 

 final stage, is accelerated by the passage of a spark, or by a 

 direct current from a battery of about a thousand volts. If the 

 conditions are right, the water particles suspended in the oil 

 cohere, at the moment of electrification, to form larger drops. 

 The frictional resistance to falling is thereby diminished, and 

 the water is consequently precipitated in and through the 

 oil. It may sometimes be seen descending in a rapid suc- 

 cession of globules, precisely as large rain-drops are precipitated 

 after thunder. About equal parts of oil and water is a good 

 proportion. The containing vessel may be either a tube or a 

 flask; it should not be more than three-quarters full of liquid. 

 This free space facilitates the mixing when the tube or flask 

 is shaken. The phenomenon is rendered much more striking 

 by colouring the oil with alkanet-root. I have to thank Prof. 

 McLeod for suggesting this pigment. 



Experiment 3. — The behaviour of a mobile conductor, when 

 electrified in a partially conducting liquid, is readily examined 

 by pouring a little mercury into a flat photographic dish con- 

 taining a stratum of paraffin-oil and water. The presence of 

 the oil is necessary to prevent the mercury from running 

 together too freely of its own accord . A battery of from, say, 

 one volt to two hundred is required, and a pair of wires to 

 dip into the dish. A reversing- key, such as is used for cable 

 transmission, may be included in the circuit. 



Suppose we begin with a large globule of mercury in each 

 of any pair of corners of the photographic dish, several inches 

 apart ; and let the globules be connected one to each pole of 

 the battery, by means of the dipping wires. A momentary 

 tap of the key causes instantaneous deformation of the mercury 

 in each corner, especially of that connected to the negative 

 pole ; and there is evident attraction between the globules. 



