696 KANSAS CITY REVIEW OF SCIENCE. 
a purple or rose-colored tint. Lieut. Arthur mentions red, and also blue light- 
ning, in his account of the Barbadoes hurricane of 1780. It has been deter- 
mined that when the cloud floats comparatively near the earth the lightning is 
white, and when occuring at great elevations the flash is of a reddish or purple 
hue. The colored tints are evidently due to the rarity of the air; for the same 
effects are produced when an electric spark is made to pass through the air of a 
partially-exhausted receiver. ; 
A certain modern philosopher says: ‘‘It is strange how strongly some errors 
retain their hold on the minds of men;”’ and the tenacious property of error is 
illustrated in the persistence with which some meteorologists uphold the theory 
that the rumblings and detonations of thunder are successive echoes reflected 
from the clouds. 
Now, as every one knows, the lightning passing through the atmosphere, 
moves in broken, zigzag lines, so that, in one part of its course it may be going 
either soward or from us, and in another in a line at right angles or obliquely to 
its former direction. From every point of its course the sound of thunder pro- 
ceeds. Now the velocity of sound is about 1,000 feet per second. Let us 
suppose a portion of the lightning’s track 2,000 feet in length lies in a line, the 
more distant extremity of which is 2,000 feet farther from us than the other, 
then will the report of the thunder be two seconds sounding in our ears; while, 
on the other hand, should the discharge occur in a line at right angles to this one, 
the report would be of but an instant’s duration—the vibrations reaching us 
from all points of the line during a single second. It is obvious, therefore, that 
in the former case, the intensity of the sound would be but half as great as in 
the latter. The different conditions of distance, direction, and intensity of the 
electric discharge are sufficient to account for nearly all the modifications of the 
voice of the thunder, which we inhabitants of the plains ever hear. In moun- 
tainous districts there are frequently echoes from mountain sides; and this is an 
effect most natural, but the idea that thunder is echoed from walls of vapor, like 
the clouds, is little short of the absurd—at any rate those should not entertain 
the idea who believe that the sound of thunder can penetrate but twice as far as 
that of a base drum. 
In some of our text-books on Physical Geography, it is stated that thunder 
is never heard at a distance of more than fez miles. ‘The truth is, thunder is not 
generally heard until the storm is within forty miles of the observer’s locality ; 
but it may be heard from one hundred to one hundred and fifty miles, if the 
conditions are favorable. When the top of the storm-cloud is about ten degrees 
above the horizon, it is then some one hundred and fifty miles distant. If the 
weather is very warm, it may be even more than this. If it is moving in the 
direction of the observer it will reach his locality within from four to six hours, 
since these storms move, as a general thing, from twenty-five to forty miles per 
hour. Some storms, however, move much more rapidly than this. One occur- 
ring in May, 1873, reached Dubuque, Ia., at 10.00 a. M., Morrison, IIl., at 11, 
and Ottawa, Ill., at noon. 
