284 Professor W, T/wmson, [^ay ^^j 



constantly extending out and gradually becoming a non-conductor. 

 The drops into which the jet issuing from the insulated conductor 

 breaks, on the plan introduced by the writer, produce the same effects 

 with more pointed decision, and with more of dynamical energy to 

 remove the rejected matter with the electricity which it carries from 

 the neighbourhood of the fixed conductor." — NichoVs Cyclopcedia, 

 2nd edition, article " Electricity, Atmospheric.''* 



After having given so much of these explanations as seemed 

 necessary to convey a general idea of the principles on which the con- 

 struction of the instruments of investigation depended, the speaker 

 proceeded to call attention to the special subject proposed for con- 

 sideration this evening. 



What is terrestrial atmospheric electricity ? Is it electricity of 

 earth, or electricity of air, or electricity of watery or other particles in 

 the air? An endeayour to answer these questions was all that was 

 offered ; abstinence from speculation as to the origin of this electric 

 condition of our atmosphere, and its physical relations with earth, air, 

 and water, having been painfully learned by repeated and varied failure 

 in every attempt to see beyond facts of observation. In serene weather, 

 the earth's surface is generally, in most localities hitherto examined, 

 found negatively or resinously electrified ; and when this fact alone is 

 known it might be supposed that the globe is merely electrified as a 

 whole with a resinous charge, and left insulated in space. 



But it is to be remarked, that the earth, although insulated in its atmo- 

 spheric envelope, being in fact a conductor touched only by air, one of 

 the best although not the strongest of insulators, cannot with its atmo- 

 sphere be supposed to be insulated, so as to hold an electric charge in 

 interplanetary space. It has been supposed, indeed, that outside the 

 earth's recognised atmosphere there exists something or nothing in 

 space which constitutes a perfect insulator ; but this supposition seems 

 to have no other foundation than a strange idea that electric conductivity 

 is a strength or a power of matter rather than a mere non-resistance. 

 In reality we know that air highly rarefied by the air-pump, or by 

 other processes, as in the construction of the " vacuum tubes," by 

 which such admirable phenomena of electric light have recently been 

 seen in this place, becomes extremely weak in its resistance to the 

 transference of electricity through it, and begins to appear rather as a 

 conductor than an insulator. One hundred miles or upwards from the 

 earth's surface, the air in space cannot in all probability have resisting 

 power enough to bear any such electric forces, as those which we 

 generally find even in serene weather in the lower strata. Hence, we 

 cannot, with Peltier, regard the earth as a resinously charged conductor, 

 insulated in space, and subject only to accidental influences from 

 temporary electric deposits in clouds, or air round it ; but we must 

 suppose that there is always essentially in the higher aerial regions 

 a distribution arising from the self-relief of the outer highly rarefied 

 air by disruptive discharge. This electric stratum must constitute very 

 nearly the electro-polar complement to all the electricity that exists on 



