AN exceptionally severe thunderstorm was experienced in London and the suburbs on the evening of the 17th inst. It commenced with distant thunder at about 5.30 p.m., and by 6 o'clock the storm was fully over the southern suburbs. The lightning was very vivid, and the flashes were very frequent, following each other occasionally with but an interval of a few seconds. The thunder was very heavy, and at times quite deafening, the crash often following the lightning-flash almost instantaneously. The greatest violence of the storm occurred between 6.30 and 8 p.m., throughout the whole of which time the lightning and thunder were most intense. Thunder was heard till 9.30 p.m., and distant lightning seen till 10 p.m., so that the storm was over London for about four hours and a half. There was no evening as far as daylight was concerned, night setting in at the close of the afternoon, and the heavy clouds which covered the sky had the appearance of being doubly massive in contrast to the lightning as the flashes illumined the whole sky. The rain which accompanied the storm was very heavy, but the fall varied very considerably in different parts of the metropolis. Unfortunately at present the measurements at hand are by no means numerous, but a careful discussion of the rainfall of this storm would probably be of considerable scientific interest. The falls as yet available are: Brixton Hill 2.02 inches, Camden Town 1.42 inch, Clapham 0.97 inch, Greenwich 0.54 inch, Westminster 0.50 inch, and East Finchley 0.16 inch. At Brixton Hill the rain was intensely heavy for twenty minutes from about 6.10 to 6.30 p.m., during which time by far the larger part of the fall occurred; the observer not being on the spot until later in the evening, measurements were not made during the progress of the storm. There is ample evidence, however, to confirm the heavy fall at Brixton, as the roads were flooded in parts to the depth of from 12 to 18 inches, and the water rushed down the roadways with such force that it was thought a large reservoir had burst. Mr. Wallis, writing from the head-quarters of the “British Rainfall” at Camden Town, states that the total fall there was 1.42 inch, and heavy rain did not commence till 6.30 p.m. He gives the following rates of fall:—7 to 8 p.m. 1.24 inch, 7 to 7.30 p.m. 0.45 inch, 7.30 to 8 p.m. 0.79 inch; in 22 minutes, from 7.42 to 8.4, the amount measured was 0.66 inch; and in 10 minutes, from 7.45 to 7.55, the heavy fall of 0.50 was measured. The primary cause of the storm was due to a somewhat shallow barometric depression, the mercury at the centre standing at 29.7 inches, which passed completely over London during the evening.