CLOUDS—LIGHT NING. 695 
heat-lightning. Lastly, if it breaks suddenly from the base of the threatening 
cloud, and spans instantaneously with a jagged chain of blinding fire the inter- 
vening space to the earth, then, it is denominated chain-lightning. Now, in 
truth, these three forms of lightning are identical, the diverse appearances which 
they present being due entirely to external conditions. 
Sometimes there occurs a form known as arborescent lightning. This is 
produced when a spark of electricity passing along the horizontal base of a cloud 
suddenly divides into several trunks, and these, sub-dividing again and again, 
produce the representation of a tree, with limbs interlacing one another in a 
_ network of fire. This form in its perfection is rarely witnessed. On the evening 
of August 6, 1870, a most magnificent exhibition of this species of lightning 
occurred. Hundreds of glittering sparks, originating from one, darted along the 
base of the storm-cloud, after the rain had passed. The aggregate length of the 
different ramifications of this single flash must have exceeded 150 miles! What 
is remarkable about this form of lightning is its comparatively slow movement. 
‘The duration of the flash on this occasion amounted to as much as two seconds; 
and, according to Arago, a flash of lightning requires only 1-288,000 part of a 
second to pass from a cloud to the earth, supposing the distance to be a mile. 
Another remarkable example of arborescent lightning occurred in June, 1870. 
In this instance, the storm was coming up from the west, though the ‘‘ fan-cloud” 
had already extended far to the east. Suddenly, far in the west, almost down to 
the horizon, in fact, the electricity originated, and, passing eastward along the 
cloud in numerous diverging and ramifying lines, finally terminated in the out- 
lying borders of the cloud, not less than szx¢y m/es from its starting point. The 
extent of this flash was greater than any other on record, so far as I know, being 
nearly five times greater than any noted by either Arago or Flammarion. The 
rumbling of the thunder continued in the west for fully four minutes after the 
flash, and no subsequent flash occurring, the sound must have been the result of 
this most remarkable discharge. The flash must have extended at least fifteen 
miles to the east of the point of observation, and forty-eight to the west of it. 
No rain was falling at the time, and none fell until an hour afterward, and then 
but very little. This was the finest exhibition of Nature’s fireworks that I have 
ever witnessed: the surpassing brilliancy of the flash and the prolonged detona- 
tions of the thunder combined to produce an effect of astonishing beauty and 
grandeur. 
I will not speak of the so-called globular lightning, as I believe it never ap- 
peared in reality, but only as the product of an excited imagination; nor will I 
make but a single remark concerning St. Elmo’s fire, that peculiar, lambent light 
which is sometimes seen on church spires. This fire, resembling phosphorescent 
light, sometimes plays lightly over the surface of depending projections of a 
storm-cloud. This phenomenon was particularly noticeable during a storm on 
the evening of June 7, 1874. 
Lightning sometimes appears of a brilliant white color, and at other times of 
