Note 36 — IV.
Reading edition
The following succinct statement of the characteristics and general laws of cyclones will be found useful by way of reference:—
1. It has been fully ascertained that in both hemispheres the air in the cyclone rotates in a direction contrary to that of the sun. Thus, in the N. hemisphere, the course of the sun being from E. to S., W., and N., the course of the hurricane is from N. by W., S., and E.; and in the S. hemisphere, the sun's course being from E. by N., W., and S., the hurricane runs from N. by E., S., and W.
2. They originate in the space between the equator and the tropics, near the equatorial limit of the trade winds.
3. There is no instance on record of a hurricane having been encountered on the equator, nor of any one having crossed the Line, although two have been known to be raging at the same time in the same meridian, but on opposite sides of the equator, and only 10° to 12° apart!
4. Their movement, which is always oblique from the equator to the poles, is usually from E. to W. at first, and towards the end W. to E., which is but a development of the gyratory motion that forms their most essential characteristic.
5. The "motion of translation" varies from so low as 9 miles an hour to 43 miles an hour. There is no precise estimate of the velocity of the gyratory motion.
6. They are liable to dilate and contract in area, the contraction always implying a great accession of violence. (See post, p. 183.)