U2 A. W. Wright— Forms of the Electrical Discharge in Air. 



has more recently obtained results similar to those there (ie<^'- 

 bed, appears to afford a satisfactory explanation of a t^in-'u!-. 

 and very interesting phenomenon which has occasional !\ ~ 

 observed in the case of objects struck by lightnino. e.-]'. . 

 of persons killed by it. A number of instances nre (»ii r 

 where the person struck was found to have iiujtress.M 

 some portion of the body a delineation of some thin- ih 

 at the time of the stroke, and a similar effect has beon n 

 also in the case of inanimate objects. Dr. Franklin m" 

 an instance in which an exact representation of a tr. 

 imprinted upon the breast of a man who was standing ' 

 when stnick by lightning. A number of similar aii.i 

 remarkable cases are cited in a paper presented to tlir !. 

 Society of England, by Mr. Andres Poey, director of the - 

 atory at Havana,* 



Mr. Varley also mentions cases reported by sea-captaii;- 

 images of certain brass numbers attached to the riggin- 

 ship being printed by the lightning upon the body of j^n- 

 killed by it, and supposes the brass numbers to have acte.l 

 negative pole in respect to the person struck. But it is uiin. 

 sary to suppose that the discharge in such cases alwavs {'i 

 ceeds from the object delineated, and many of the instances 

 recorded forbid such a supposition. The experiments in the 

 production of the electrical shadows show that it is merely 

 necessary that the object should interrupt the lines of action ot 

 the electricity, and that it may be at a considerable distance 

 from the electrified cloud, the chief and indispensable condi- 

 tion being that the latter should be negatively electrified. "V\'e 

 should then have the body exposed to the lightning positive' 

 electrified by induction, and, as the tension became suffici- 

 the dark discharge i 

 followed by the ligt 



in the path of the ( 

 glow, and this might, in rare cases like those recorded, be > 

 ciently intense to leave a permanently visible impression, 

 fact that the image in many cases is very much reduced in f 

 shows indeed that the cloud, or other body servnng as the i 

 ative pole, is much more distant from the object represei 

 than is the bbdy struck, for in the experiments described in 

 former paper, it was found that the image of the paper ,<:r: 

 grew much smaller as it approached the positive pole, and. 

 effect would be likely to be still more marked where the v.- 

 tive body had a vei-y extended surface, as would be the ^ 

 were it a cloud. 



In some experiments recently made, the negative pole of 



machine was covered with several folds of woolen flannel wl 



* See an abstract of this paper in the Ann. Sci. Discoverj, 1858, p. 226. 



