Om Elektriske Gnister I
Gnistforsinkelse

62 Nr. 10. P. O. Pedersen: herom følgende: »The cause of “hardness” was connected with some very easily variable surface condition of the plug. It had nothing to do with the geometrical form or material. The hardness was liable to change with the most trivial alterations; it usually seemed much easier to make a soft plug hard than to make a hard plug soft«. (S. 226). »Hardness is a property of the cathode only. No treat- ment of the anode will ever change a gap from soft to hard or vice versa.....A gap may thus be hard in one direction but soft in the other. The circumstances which make a cathode hard are exceedingly various and difficult to define in detail; but their general nature was obvious. Thus a cathode could always be made hard by rubbing it with fine oily emery- paper; it could usually be made soft again by heating to redness in a Bunsen flame.....A freshly turned surface was usually soft. Hardness is therefore due to some ad- herent film on the surface which usually consists of oily matter; but it seemed that the state of the atmosphere exerted some influence, for on some days it was impossible to make any gap really soft.« (S. 228). »Two practical hints for abolishing hardness may be given. First it is a good plan to allow a strong spark to pass between the electrodes for a few seconds immediately before observations; second it is a very bad plan to clean electrodes by rubbing with fine emery cloth. Unless the surface is actually pitted, discoloration due to previous discharges is positively an advantage; to rub the surface with fine emery is to rub the “hard” film in rather than to rub it off, and so to prevent its removal by other means.« (S. 230). Norman Campbell er saaledes fuldt ud klar over, at det først og fremmest er Katodens Renhed, det kommer