344 



NA JURE 



[February 8, 1900 



near, with the discharges connected with it, and the discharges 

 belonging to several very distant arc lamps, of which five are 

 seen to the right and a few to the left of the former. Fig. 3, 

 which points a little more to the north, takes in an arc lamp at 

 an intermediate distance. These figures, as before, point out very 

 .strikingly the similarity of the discharge from lamp to lamp, and 

 the difference from flash to flash. 



Thus, in Fig. 2, we have a nearly vertical discharge from the 

 near lamp, and also from the distant lamps, whereas in Fig. 3 we 



have the corresponding discharges nearly horizontal, somewhat 

 resembling parabolas in a horizontal plane. In these cases, 

 unlike that of Fig. i, there is a discharge of curious form which 

 is more conspicuous than the discharge between the lamp and 

 the ground. 



The finer beading naturally cannot be shown in the reproduc- 

 tion, though it appears in very many cases in the positive copies, 

 and still belter in the original negatives. After an examination 

 of the actual photographs, one is 

 disposed to regard the beading as a 

 nor.ntial feature of this kind of dis- 

 charge, though for different reasons it 

 cannot always be traced. 



Fig. 5 was taken towards the sea, 

 facing the installation for ornamental 

 incandescent lamps just opposite to 

 Mr. Webb's house. The flash wliich 

 occasioned the local discharges is seen 

 in the field. Some luminosity is seen 

 at the top connected with the mount- 

 ing of the ornamental lamps, and 

 delicate discharges going obliquely 

 downwards. But the chief luminosity 

 would seem to have relation to the 

 high-tension cable below, and it may 

 be also to one or both of the hori- 

 zontal wires above, across which the 



lamps are hung, and which are charged through transformers to 

 a much lower tension. 



The complicated Fig. 6 represents five flashes, all apparently 

 in the field, and the local effects due to them. At the risk of a 

 digression, I would point out the character of one of the flashes 

 — that shown in the middle of the field — though what I am 

 about to say can hardly be gathered from the reproduction, but 

 appears in a positive photograph, or, better siill, in the original 

 negative. The actual photographs give strongly the idea of a 

 spark-discharge, the path of which is the right-hand boundary 



in the picture, followed by a transverse flow, or arc-discharge, 

 from right to left, all over the path of the spark ; then a second 

 spark-discharge, parallel to and less strong than the former, 

 followed by a second transverse flow. Previous photographs 

 taken with a moving can:era had shown a duration of luminosity 

 after the spark-discharge, which would naturally be interpreted 

 to indicate either a sort of phosphorescence of the air, produced 

 by the spark-discharge, or else an arc-discharge proceeding 

 along the path opened up for it by the spark. But Mr. Webb's 

 photograph, the original of Fig. 6, 

 seems to indicate pretty plainly an 

 arc-discharge proceeding, with a 

 variable intensity, from the different 

 points of the ])ath of the spark, hut 

 flowing in a direction transverse to 

 that path. 



The local effects, which form by 

 far the greater part of the luminosity 

 represented in Fig. 6, are naturally 

 very complicated, on account of the 

 number of flashes ; too much so to 

 be convenient for individual dis- 

 cussion. We may notice, however, 

 in a general way, the repetitions of 

 the same form and the beading. A 

 prominent object is the very formid- 

 al;le-looking discharge shown in the 

 left half of the picture, traces of the 

 beading of which may be seen even 

 in the reproduction. 



In several cases the photographs 

 indicate pretty plainly a local dis- 

 charge of the form of tape striped 

 across. The tape in its course is 

 liable to be bent or twisted, or both. 

 In places where the plane of an ele- 

 ment of the tape is in the line of 

 sight, the striping is not usually seen, 

 as the bright and dark stripes would 

 overlap unless the axis of the tape 

 happened to be roughly perpendicular 

 to the line of sight. 



In connection with the phenomena 

 ])resented by the electric lamps in a 

 thunderstorm, as revealed by the photographs, several theo- 

 retical questions present themselves. Do the lamps act 

 merely in consequence of the tall iron lamp-posts, so that 

 the effect would be the same if the dynamos at the works were 

 not in action, or is the artificial electricity concerned in the 

 production of the effects? What is the nature of the action of 

 the flash of lightning in l)ringing about the discharges? What 

 determines the course of the discharge, and why is it so 



different from flash to flash, while for a given flash it is nearly 

 the same for lamps ranging over a space of some hundreds of 

 yards ? What is the nature of the beading or striation ? 



As the lamps are wanted for public lighting, the experimeoif 

 could not well be made of disconnecting one from the works 

 when a thunderstorm was impending in the evening, and seeing 

 whether the one disconnected would give a discharge like the 

 others. In default of experiment I can only say that from my 

 theoretical notions I think that the electrical action of the lamps 

 is required. 



NO. 



1580, VOL. 61] 



