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mechanical means by which the pollen is conveyed from one flower to 

 another, some plants having the pollen wind-borne (anemophilous), others 

 having it conveyed by insects (entomophilous). These facts involve a 

 variation in the form of the pollen grains themselves, and in the quantity 

 of pollen to be produced by the respective genus or species. Eefereuce was 

 also made to the labours of Darwin, Lubbock, and others in this absorbing 

 subject. 



July 3rd, 1885. 



T. FAIRLEY, F.R.S.E., on "THE ELECTRIC DISCHARGE 

 IN AIR AND OTHER GASES." 



After defining the meaning of some of the terms used, the speaker 

 showed that when a conductor is charged with electricity of high tension, 

 a limit at length occurs when the electricity forces its way through the 

 air or other dielectric medium to the nearest conductor. 



If this takes place rapidly with air at ordinary pressures a spark is 

 produced, as in ordinary lightning. This spark discharge is modified by 

 the form of the conductor, and by the currents of air set up, into a brush 

 which may be most readily obtaiaed from a positively charged obtusely 

 pointed conductor, or into a glow best shown by the luminous air-current 

 from a negative conductor. 



In air when the pressure is diminished up to a certain limit the dis- 

 charge takes place more readily, and at greater intervals between the poles. 

 In the extreme case Morgan showed 100 years ago that no spark passes in 

 the Toricellian vacuum. Under increased pressures above that of the 

 atmosphere the electric discharge takes place with greater difficulty, so 

 that the striking distance becomes greatly diminished. 



The spark discharge is shown as a thin streak of light, straight in short 

 sparks, zigzag in larger sparks. Its duration by one mode of testing is 

 l-24,000th part of a second. Its colour varies with the poles, and the 

 medium through which it passes ; thus, in air it has a bluish tint ; iu 

 nitrogen, purple ; oxygen, whiter than nitrogen ; hydrogen, crimson ; 

 carbonic acid, green ; and coal gas, red or green. 



The brush or broom discharge occurs most readily when one conductor 

 is projecting, but not pointed, and the other is a plate or larger surface. 

 It is intermittent, and attended by a hissing noise. 



The glow, convective or silent discharge is continuous and without 

 noise. The glow is best seen near to the negative conductor, and less on 

 the positive, with a dark interval between. Recently, Professor O. Lodge 

 has shown that this glow discharge has a wonderful power in condensing 

 and precipitating vapours, or any finely divided particles in suspension. 

 The glow is no doubt a visible manifestation of what takes place when the 

 surfaces are larger, and show no glow. When the glow takes place in 

 ordinary smoke, the air currents produced by the discharge are well shown. 



