7. Belt of condensation.
8. Cool northerly wind.
And so on, successively, unless broken in upon by some other class.
Sometimes these periods are exceedingly regular, at other times the other classes prevail. I have much reason to believe that this is the normal, periodic provision for condensation of our portion of the northern hemisphere, and probably of every other where rain falls regularly in the summer season, and that the other classes are exceptions, as the hurricanes are exceptions to the normal condition of the weather every where. Perhaps in some seasons, during the northern transit, the exceptions may equal the rule, but I do not now remember such a season. In other years nearly all the storms are of this character. Thus, Dr. Hildreth (in Silliman’s Journal for 1827), speaking of the year 1826, in a note to his register of that year, says: “There have been, this year, an unusual number of winds from N. or N. W. Nearly every rain the past summer has been followed with winds from the northward, when, in many previous summers, the wind continued to the southward after rain.” The immediate occurrence of northerly wind after the passage of the belt of condensation, is a peculiar feature of this class of storms.
As this also will be new, and is of great practical interest, I shall be pardoned for referring to other evidence. Bermuda is in latitude 32° north. In the summer season they are within the range of the Calms of Cancer, as Lieutenant Maury terms them, and not subject to storms. From November to May, inclusive, they have successions of revolving wind. Colonel Reid gave them much attention, and studied them barometrically: that is, he studied the changes of the wind during the successive periodic depressions. He found them revolving like ours, and hence inferred the truth of the gyratory theory in relation to all winds. But it is perfectly evident the same polar belts which pass over us reach them during the southern transit. The precedent southerly wind, the central condensation, the appearance of lightning, and the rotation of the wind by both the east and west, but most frequently by west, are the same. In his chapter on observations at the Bermudas, he gives us many examples. Probably the existence of the Gulf Stream to the west and north has a modifying influence upon them, and their action becomes less intense in that latitude, but they are very similar. I copy a record of the weather, for a month, which may be found on pages 252, 253, and 254, and a portion of his remarks:
“The month of December, 1839, presents a continual succession of revolving winds passing over the Bermudas, with scarcely an irregularity, as regards the fall and rise of the barometer accompanying the veering of the wind. One, however, occurred on the 10th and 11th. The S. W. wind abated, and changed to W. N. W., with the barometer still falling. But in the column of remarks it is noted that there was lightning seen in the N. and N. W., from 7 P.M., during the night. This irregularity may, therefore, have been occasioned by a gale passing over the banks of Newfoundland, influencing the direction of the wind at Bermuda.
“REVOLVING WINDS.
| Date. | Hour. | Direction of Wind. | Wind’s Force. | Weather. | Bar. | Ther. |
| 1839. | ||||||
| Nov. 30 | Midnight. | S. S. E. | 1 | b. c. | 30·06 | 65 |
| Dec. 1 | Noon. | S. S. W. | 3 | b. c. | 30·07 | 71 |
| 2 | " | S. W. | 5 | g. m. q. | 29·86 | 70 |
| 3 | " | S. S. W. | 3 | g. c. | 29·76 | " |
| 4 | " | S. W. | 6 | g. m. r. | 29·62 | 68 |
| 5 | " | W. N. W. | 5 | p. q. | 29·56 | " |
| 6 | " | N. W. | 6 | p. q. | *29·55 | " |
| 7 | " | N. N. W. | 5 | b. c. | 29·78 | 70 |
| " | Midnight. | N. N. W. | 3 | b. c. | 29·89 | 68 |
| 8 | Noon. | W. N. W. | 2 | b. c. | 29·82 | 71 |
| 9 | " | S. S. W. | 5 | p. q. | 29·84 | 70 |
| 10 | " | S. W. | 2 | b. c. | 29·96 | " |
| 11 | " | W. N. W. | 6 | b. c. m. | *29·88 | 68 |
| 12 | " | S. S. W. | " | b. v. | 29·99 | 69 |
| 13 | " | N. N. by W. | " | b. v. | 30·01 | 66 |
| 14 | " | N. N. W. | 5 | b. c. v. | 30·06 | 64 |
| " | Midnight. | N. W. | 2 | b. c. p. | 30·05 | 63 |
| 15 | Noon. | S. W. by S. | 6 | g. m. r. | 29·72 | 65 |
| " | P.M. 2 | S. S. W. | 7 | m. q. r. | 29·92 | 64 |
| " | " 4 | S. S. W. | " | g. m. q. r. | 29·55 | " |
| " | " 6 | W. S. W. | " | q. w. | *29·53 | " |
| " | " 8 | N. W. | 6 | b. c. q. | 29·54 | " |
| " | " 10 | N. N. W. | " | b. c. | 29·55 | " |
| 16 | Noon. | N. W. | 7 | b. c. m. | 29·53 | 62 |
| 17 | " | N. W. by N. | " | p. q. | 29·67 | 60 |
| 18 | " | N. W. | 6 | c. q. | 29·86 | " |
| 19 | " | N. W. by N. | 7 | m. q. r. | *29·73 | 59 |
| 20 | " | N. N. W. | " | p. q. c. | 29·89 | 58 |
| 21 | " | N. W. by N. | 6 | c. q. | 29·96 | 56 |
| " | Midnight. | S. W. | 1 | b. c. | 29·95 | 55 |
| 22 | Dawn. | —— | 0 | |||
| " | Noon. | S. S. W. | 5 | g. m. | 29·83 | 56 |
| " | P.M. 4 | S. | 7 | g. m. | 29·79 | " |
| " | " 6 | S. S. E. | " | g. m. r. | 29·61 | " |
| " | " 8 | S. S. E. | " | w. r. | 29·52 | " |
| " | " 10 | S. E. | " | m. w. r. | 29·48 | " |
| 23 | Noon. | S. W. | 6 | b. c. m. | *29·44 | 57 |
| 24 | " | W. N. W. | " | b. m. | 29·71 | 59 |
| 25 | " | W. N. W. | 5 | b. c. | 29·88 | 56 |
| 26 | " | N. | 3 | c. | 30·09 | 62 |
| 27 | " | S. E. | 5 | c. q. r. | 30·07 | 61 |
| 28 | " | S. W. | 6 | c. q. | 29·88 | 66 |
| " | Midnight. | S. S. W. | " | b. c. | 29·76 | 65 |
| 29 | Noon. | S. W. | 7 | c. b. | *29·48 | 64 |
| 30 | " | W. N. W. | 6 | b. c. q. | 29·83 | 55 |
| 31 | " | N. W. | 5 | b. c. | 30·12 | 58 |
“Remark printed in the Register.
“The changes of the wind during the December gales have been nearly the same in all: i. e., commencing with a southerly wind at first, the wind has veered by the west, toward the north-west, sometimes ending as far round as N. N. W.”