lO 



NA TURB 



[May 6, 1875 



four inches square) should be put into a strong sohition 

 of soap, and wiped dry with a duster. If a plate be then 

 held by the corner against the knob of a small charged 

 jar, and, with one knob of the discharging rod resting 

 against the outer coating, the other be brought up to the 

 knob of the jar with the glass between, the spark will 

 pass over the surface of the pane, turn over its edge, and 

 thus arrive at the knob of the rod. Nothing is visible on 

 the plate until it is breathed on, apd then the condensed 

 breath settles in the form of minute dew on those parts 

 of the soapy film that have not been burnt off by the 

 electricity, while on the lines that have been burnt off or 

 made chemically clean the moisture condenses in watery 

 lines, bringing out the trunk, branches, and minute spray 

 of the dendritic figure in a very perfect manner. In the 

 discussion that followed the reading of my paper, the 

 president of the section remarked that the figures ex- 

 hibited would pass for trees all over the world. The dis- 

 charge sometimes exhibits bifurcations and even trifurca- 

 tions. The main trunk is evidently a hollow tube, as in 

 the vitrified masses known as fulgurites, where lightning 



Fig. I.— Breath Figure of Electric Discharge (also called Jioric FigJire, 

 iromRos-ro7is, "dew.") 



ploughs through a sandy soil. Should the plate be too 

 thick, the main discharge may not pass, in which case the 

 plate represents spray only. Hence I infer that the spray 

 precedes the discharge and acts as a feeler for the line of 

 least resistance. Indeed, it is an old observation of 

 sailors, that before the ship was struck everyone on board 

 felt as if cobwebs were being drawn over his face. 



The accompanying (Fig. i) is one of the figures produced 

 as above described, the separate figure being an enlarged 

 portion of the stem or trunk which represents the main 

 discharge. Other examples may be found in the "Eng- 

 lish Cyclopaedia " (Arts and Sciences division), article 

 "Breath Figures," and in the Edinburgh Neiv Philoso- 

 phical Journal for October 1861. 



After the reading of my paper I was anxious to see 

 some examples that had been undoubtedly produced by 

 lightning of these ramified figures. I was gratified by 

 the receipt of a letter from Dr. Pooley, of Weston-super- 

 Mare, informing me that he had actually seen a tree 

 struck by lightning, that the inner surfaces of the de- 



tached bark contained ramified figures such as I had 

 described, and that he had sent specimens to Dr. Fara- 

 day. I accordingly applied for permission to examine 

 them. The figures on the bark had become very faint, 

 but the following engraving (Fig. 2) represents their 

 character. 



In the Lancet of July 30, 1864, Dr. D. Mackintosh 

 describes a case in which a straw stack was struck by 

 lightning and set on fire, while a man who had sought its 

 shelter was killed, and two boys injured. One of the 

 boys, aged ten, said he felt "dizzy all over;" his legs 

 would not carry him, and he felt pain in the lower part of 

 the abdomen. On taking off his clothes a pecuhar sul- 

 phurous singed odour was perpectible, and also several 

 irregular but distinct red streaks, of about a finger's 

 breadth, running obliquely downwards and inwards on 

 either side of the chest to a middle line in front of the 



Fig. 2. — Three Portions of the Inner Surface of the Bark. 



abdomen, whence they converged ; from this point they 

 diverged again till they were lost in the perineum. The 

 streaks were of a brighter red on the more vascular parts 

 of the body ; they disappeared in about four days, and 

 the lad recovered. 



In the second case, that of a boy aged eleven, "the 

 figures on either hip were so exceedingly alike and so 

 striking, that an observer could not but be impressed 

 with the idea that they were formed in obedience to some 

 prevailing law." 



In the third case, that of a man of forty-six, the dis-* 

 charge passed through the head, and seems to have pro- 

 duced instant death. 



The phenomena in the case of the two boys agree very 

 well with those described in Mr. Pidgeon's letter. 



But there are various other figures produced by light- 

 ning sufficiently numei.ous to have led M, Baudin, in his 



