PHYSICS. 125 



this wire is 0.0095 inch, and in the two outer ones 0.0115 and 

 0.0110 inch. The condenser consists of 126 sheets of tin-foil 

 18 by 8.5 inches, separated by two thicknesses of varnished 

 paper 0.0055 inch thick. Glass 3 inches thick lias been 

 pierced with the 28-inch spark of this coil, using five cells 

 of Grove. 



Spottiswoode also has experimented to determine the con- 

 ditions of stratification in exhausted tubes, and finds that in 

 a tube, one terminal of which is connected with the negative 

 coating of a Leyden battery, while the other is held beyond 

 striking distance from the positive coating, the discharge 

 will show the separation of the positive from the negative 

 part by a dark intervening space, and under suitable condi- 

 tions of exhaustion will also show striae. Decreasing the 

 distance from the positive coating produced a stratified dis- 

 charge. He concludes that by a suitable disposition of a 

 Leyden battery the phenomena produced by it coincide with 

 those produced by the induction coil. 



Thompson has repeated and varied the experiments of 

 Edison on induced sparks, from which the latter concluded 

 upon the existence of an "etheric" force. He has obtained 

 these sparks ten millimeters long, and shows that they are 

 made up of alternating currents of very short duration. 



Lommel has figured two interesting electric dust figures 

 analogous to those of Lichtenbero;, but in which the rod con- 

 veying the discharge lay horizontally on the vulcanite plate 

 instead of being vertical. One of these is positive, the other 

 negative, and they were produced by dusting a mixture of 

 red-lead and lycopodium powder on the plate after several 

 sparks had passed into the rod. 



Wright has studied the production of transparent metallic 

 films bv the electric discharge in exhausted tubes, and has 

 obtained some curious results. The colors obtained by trans- 

 mitted light were, for gold, brilliant green, thinning out to 

 pinkish violet ; for silver, pure deep blue ; copper, dull green ; 

 bismuth, grayish blue; platinum, gray; palladium, smoky 

 brown ; lead, olive brown ; zinc and cadmium, grayish blue, 

 inclining to purple ; aluminum, brownish ; iron, neutral tint ; 

 nickel and cobalt, gray or brownish gray ; tellurium, purple ; 

 magnetite, gray brown. The light transmitted is power- 

 fully polarized, the polarization increasing with the incident 



