W.P. Pratt¹ to Faraday   2 March 1840

March 2nd 1840

Sir,

I am much obliged by your reply to my note, Feb 3rd², but circumstances have prevented me forwarding the further information I promised 'till the present moment.

In the monthly Meteorological journal published in the Metropolitan, June 1839 is the following entry - May 8th Thunder Storm, Wind N.E. Weather generally clear except the evening about 1/2 past 7 till about midnight a terrific thunder storm accompanied by the most vivid lightning & heavy rain - From midnight till about 2 O'clock in the morning of the 9th distant thunder & lightning³.

The first flash, the form of which I could see distinctly, was soon after the storm had commenced. I was passing through Lambeth, towards the East, but I could see only a portion of the flash (the commencement & finish being hid from my view by the houses on each side) it was very distant but distinct and proceeding horizontally from East to North in a waving form with short branches from the principal stream finding the storm likely to continue, I turned and proceeded home, but nothing particular occurred to arouse my attention till near 11 O'clock, when perceiving the storm was very violent, I left my room & opening the back door of the house, remained for some time gazing on the splendid flashes of lightning, the first few from their sudden brilliancy were scarcely perceptible but after a few moments my sight became sufficiently accustomed to trace the lightning in its rapid course, the flashes were all of the waving form & proceeding horizontally from E. to N. till attracted by the earth, when they descended in the waving form, but with a degree of curvature sometimes forming 1/2 an arch sometimes less. The degree of curvature seeming to depend on the length of its horizontal motion, before it struck the earth. The last flash, that I remained to see, was one of most vivid brilliancy when it had half completed its horizontal course a branch came waving to earth curved about 1/4 of an arch, when the remainder had completed its horizontal course, it descended curved, about 1/2 an arch, thus appearing the greater the length of its horizontal course, the greater the curvature of its descent - after it had vanished, still, a vivid picture remained on my sight for several seconds. The only object apparently visible was the bright stream of waving light its horizontal course its two branches waving to the earth, with their difference of curve, all apparently fixed 'till it vanished when I could instantly see the objects around me. I then retired to rest. With regard to the other points you mention, the latter flashes were apparently in the immediate vicinity thunder followed each flash all the flashes appeared curvilinear. I did not observe in any an approach to that acute angularity, necessary to constitute the zig-zag form of lightning. I believe the storm was fatal, but I have none of the papers, of the time, by me at present. What appeared to me most remarkable in the lightning was the apparent polar attraction conjoined with that of the earth in its immediate vicinity. Has such apparent double attraction been noticed, or, supposed to exist - Could the Daguerreotype be made available to ascertain the real course of motion - What has been the impression on your own sight after the lightning has vanished - Are you acquainted with a theory that would account for a zig-zag motion?

A reply to the above questions would very much oblige

Yours &c | W.P. Pratt

20 Ossulston Street | Somers Town

M. Faraday Esq