Observations on some Experiments in Electricity. 57 



form have caused them to be mistaken for ancient tombs, by suppo- 

 sing that they were formerly the center of a vortex of water ? 



It may be inferred from the preceding experiments and observa- 

 tions, that the cause of water spouts is purely mechanical, and that the 

 movement of the air alone, is sufficient to produce them ; but in dis- 

 carding electricity, as the immediate cause of the phenomenon, it does 

 not follow that it may not be a remote cause, since it is possible that 

 this agent assists much in the formation of whirlwinds and of winds 

 which produce them. 



Art. VI. — Observations on some Experiments in Electricity ; by 

 Walter R. Johnson, Professor of Mechanics and Natural Phi- 

 losophy in the Franklin Institute, Philadelphia. ' 



1. The electric spark. 



The appearance of the electrical spark, passing through air, has 

 been observed with considerable attention by philosophers, and the 

 various phenomena of its luminous track marked, with a reference 

 to certain theories respecting the nature of the principle by which 

 they are occasioned. The brush and the star, were formerly con- 

 sidered almost conclusive in favor of Franklin's hypothesis. The 

 experiment of Cavallo and Singer, in which a pith ball laid in a non- 

 conducting groove, is propelled towards the negative point of the 

 discharger, has also been cited in favor of the saine theory, as well 

 as the direction of the flame of a taper placed between two balls 

 oppositely charged, and that of the revolution of a light float wheel, 

 acted upon by the electrical current. But since it has been discov- 

 ered that some bodies have different conducting powers in reference 

 to the two opposite electricities, or " electrical states," it has been 

 doubted whether the above cited experiments afford any decisive in- 

 dications in regard to the point in question. 



There is, however, one interesting phenomenon which is not recol- 

 lected to have been fully described by any writer on the subject.* It 



■ fcsome notice of the neutral point, has been tal^en by Berzelius, and a more distinct statement 

 respecting it, is made by Dr. Thomson in his treatise on heat and electricity. The former in the 

 1st vol. of his Chemistry, (Paris edit. p. 106,) maintains that " the spark is not a mere transmission 

 of the electricity of an electrified body, to a conductor which it approaches. It is composed of the 

 positive electricity of one of the bodies, and the negative electricity of the other, which unite and 

 form an equilibrium at some point in the space which the spark seems to traverse. If the body 

 which approaches the conductor, be uniformly rounded, tho spark appears in the middle of the 

 epace between the two bodies. * ' ' At this point of i/n?on, the spark swaps and all the elec- 

 trical phenomena cease." Thomson's language, (Lond. edit. p. 471,) is, "if the spark be very 

 long, the middle part of it is not illuminated at all, or only very slightly. Now this imperfectly 

 illuminated part, is obviously the spot where the two electricities unite, and it is in consequence 

 of this union, that the light is so imperfect." Notwithstanding these authorities, (which were not 

 consulted in regard to it, until long after my own observation had convinced me of the existence 

 of the neutral point,) I have seldom found an electrician who was willing to believe in the exist- 

 ence of the said point until I had shown him the experiment. 



Vol. XXV.— No. 1. 8 



