589. When is the flash of lightning straight?
When the distance between the clouds whose electricities are meeting, is small.
590. What is the cause of the aurora borealis?
The mingling of the electricities of the higher regions of the atmosphere.
591. When does the flash of lightning appear blue?
When the degree of electrical excitement is intense, and general throughout the atmosphere.
592. Why does lightning sometimes appear red, at others yellow, and at others white?
Because of the varying humidity, which affects the refracting power of the atmosphere.
593. Does lightning ever pass upwards from the earth to the clouds?