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X. Intelligence and Miscellaneous Articles. 



ON ELECTKICITT PRODUCED BY THE FRICTION OP DROPS. 

 BY J. ELSTER AND H. GEITEL. 



HHHE authors sum up the results to which their investigation leads 

 ■*- as follows : — 



(1) If the current of a spray-producer is directed against a solid 

 wetted with water, any electrification which may be observed must 

 not necessarily be attributed to friction against the surface. In 

 this mode of arranging the experiment, the inductive action of even 

 very low tensions in the air exerts a preponderating influence. 

 Even where the droplets are leaving the mouth of the spray- 

 producer in the unelectrified condition, -the plate which receives- the 

 droplets must be charged by induction to the potential of the 

 neighbourhood by the droplets. 



It follows from this that experiments on the excitation of elec- 

 tricity by the friction of drops must be received with the greatest 

 reserve, if suitable measures are not taken to eliminate the electro- 

 motive forces produced by induction, or to make an allowance for 

 the disturbance which they produce, a problem the complete solu- 

 tion of which has hitherto failed us. 



(2) On some bodies on which there is no wetting, the excitation 

 of electricity by friction preponderates so considerably over that by 

 induction that the influence of the latter may in most cases be dis- 

 regarded. 



To these bodies belong those whose surface is coated with wax, 

 shellac, sulphur, or fat. The leaves of certain plants were found 

 to be particularly active. 



A jet of water which disperses in drops acts like a spray- 

 producer. 



(3) If metal plates are coated with liquids which do not moisten, 

 a powerful electrification may be imparted to them by causing an 

 extremely fine jet of water to glide over them in such a way that the 

 place of dispersion is over or on the plate. Eor the success of this 

 experiment it is necessary that the electrical layer should be a good 

 insulator. If this is not the case, as, for instance, with the leaves 

 of plants, electrification is only found in the discontinuous part 

 of the jet. In all the cases mentioned under (2) and (3) the 

 rubbed body is negative, and therefore the water is positive. 



(4) Bodies of such high temperature that Leidenfrost's drops 

 form on them may also be electrified by friction. All the circum- 

 stances which favour the occurrence of the spheroidal condition of 

 a liquid, also produce an increase of the electromotive force at the 

 place at which the solid and liquid surfaces are in contact. In this 

 the electrification of hot water is negative ; when the spheroidal 

 condition ceases it is positive, and below 110° to 120° there is no 

 appreciable disengagement of electricity. 



The deportment of ether is analogous ; at the ordinary tempera- 

 ture it electrifies the rubbed body positively, and at higher tempe- 

 ratures negatively, 



