Note 17 — SECTION SECOND.

This day the central vortex passed in about latitude 47° N.—the southern margin cannot be nearer than 250 miles, throwing off the 40′ for the horizontal refraction, would give eight miles of altitude above a tangential plane. Then another seven miles, for curvature, will give an altitude of fifteen miles for the cumuli. The height of these thunder-clouds has been much under-estimated. They seem to rise in unbroken folds to a height of ten and twelve miles frequently; from the data afforded by the theory, we believe they will be found much higher sometimes—even as much as sixteen miles.