ELECTRICAL ACTION. IN VACUO. 243 



mitting the air, the wire was immediately fused by only a single jar, exposing not 

 more than five square feet of coating. 



78. It would therefore seem impossible to prevent the flow of electricity between 

 bodies in a space altogether void of resistance, so long as the least attractive force is 

 exerted between them, or otherwise to restrain a similar current, in a less perfect 

 void, with an attractive force between the bodies proportionate to the square of the 

 density of the resisting medium. I have succeeded, by means of a very powerful 

 electrical machine, in the transmission of continuous electrical streams through long 

 exhausted tubes of above four inches in diameter and upwards of six feet in length. 

 The phenomena, beside being very instructive, were of peculiar beauty. The extre- 

 mities of the tubes were ground airtight to brass plates, A «, fig. 28, each plate being 

 furnished with a projecting point. When this long receiver was moderately ex- 

 hausted, and the plates connected with the positive and negative conductors of the 

 machine, luminous streamers ensued, branching upon the sides of the receiver toward 

 the negative plate. When the upper plate A was connected with the positive con- 

 ductor, and a with the negative, the currents appeared as in fig. 29 ; and when these 

 connexions were reversed by connecting A with the negative conductor, and a with 

 the positive, the currents appeared as in fig. 30. If either of the plates had its con- 

 nexion with the negative conductor removed, so as to leave it insulated, then the 

 flowing from the opposite plate ceased. As the exhaustion was more complete, the 

 distinctions of the branches gradually became less, so that finally the whole interior 

 surface of the glass was covered with a continuous mass of white light. 



In no case did the electricity appear to be transmitted through the intermediate 

 space, except in the act of flowing from the points upon the interior surface of the 

 glass : when it is possible, liowever, to cause the electric matter to pervade the par- 

 tially exhausted space, it is frequently attended by a sort of beautifully luminous 

 glow. 



79. Much discussion has occasionally arisen in this department of science respecting 

 the conducting power of a vacuum ; but surely this must be regarded as a somewhat 

 anomalous form of expression. If by a vacuum we are to understand the absence of 

 all matter, and to consist in mere vacant space, it seems unphilosophical to suppose 

 it endowed with any positive quality whatever. It cannot, therefore, have either con- 

 ducting or insulating properties, but must be a mere passive condition, under which 

 an electrified substance may be imagined to be placed. Hence, as already stated (74.), 

 an attractive force, however small, exerted between two bodies so circumstanced, 

 must cause electrical currents to flow through a distance however great ; the only 

 difference would probably be the absence of the electric light usually observed in 

 transmitting electricity through an imperfect void, as may be gathered from the fine 

 researches of Sir Humphry Davy on this subject *=. 



80. With a view of accommodating the phenomenon of electrical divergence to the 



* Philosophical Transactions, 1822, p. 64. 



