14 



REPORT — 1856. 



On the Form of Lightning. By James Nasmyth, F.R.A.S. 

 Mr Nasmyth said, that, observing that the form usually attributed to lightning by 

 painters and in works of art was very different from that which he had observed as 

 exhibited in nature, he was induced to call attention to .t. He believed the error of the 

 artists originated in the form given to the thunderbolt in the hand of Jupiter as sculp- 

 tured by the early Greeks. 

 The form of lightning as 

 exhibited in nature was 

 simply an irregular curved 

 line, most generally shoot- 

 ing from the earth below to 

 the cloud above, and often 

 continued from the cloud 

 downwards agai n to another 

 distant part of the earth. 

 This appearance, he con- 

 ceived, was the result of the 

 rapid passage of a point of 

 light which constituted the 

 true lightniug, leaving on 

 the eye the impression of 

 the path it traced. In very 

 intense lightning, he had 

 also observed offshoots of 

 an arborescent form to pro- 

 ceed, at several places, from 

 the primary track of the 

 flash. But in no instance 

 among the many thunder- 

 storms whose progress he 

 had most attentively watch- 

 ed, had he ever observed 

 such forms of lightning as 

 that usually represented in 

 works of art ; in all such, 

 the artists invariably adopt 

 a conventional form, name- 

 ly, that of a zigzag com- 

 bination of straight lines as 

 indicated in fig 1 ; whereas 

 the true natural form of a 

 primitive flash of lightning 

 appears to Mr. Nasmyth 

 to be more correctly repre- 

 sented by an intensely 

 crooked line, as indicated 

 in fig. 2 ; and on several 

 occasions he has observed 

 it to assume the forked or 

 branched form indicated in 

 fig. 3 ; but, as before said, 

 never in the zigzag dovetail 

 of fig. 1. Mr. Nasmyth 

 also remarked, that in the 



maioritv of cases he had j .i. -u 



observed that the course of the flash was from the e^rth upwards towards the heavens. 

 He used the term "primitive flash" to distinguish it from "sheet lightning, 

 which is generally the reflexion on light ditf-used from a hidden primitive flash. 



1 



