Q. Which part of the collapsing air do we hear first?
A. That part nearest the earth; then the strata above; and last of all, that in the immediate vicinity of the cloud.
Q. What is meant by “strata of air?”
A. If a board were laid upon the earth, and several other boards were piled upon it, this pile would represent strata of wood.
Q. How does this illustration apply to the air?
A. A layer of air covers the earth; another layer rests upon it; and thus layer is piled upon layer, for 50 miles in height. Each layer is a “stratum” of air; and the plural of stratum is strata.
Q. Why do we hear the collapsing of the air nearest the earth first?
A. Because sound takes a whole second of time to travel 380 yards; but the air is ripped from top to bottom instantaneously: if, therefore, the cloud were 1000 yards off, we should hear the collapsing of the lowest strata nearly three seconds, before we heard that in the immediate vicinity of the cloud.
Q. Why is the thunder sometimes like a deep growl?