| Date. | Wind. | Force. | Ther. | Bar. | Sky and Weather. |
| Jan. 3 | ...... | calm | -26.1 | 29.62 | blue sky, m. |
| "4 | W. | gent breeze | -21.3 | 29.53 | blue sky, detached clouds, m. |
| "5 | W. by N. | gent breeze | -3.9 | 29.59 | blue sky, m., clouded over. |
| "6 | W. by S. | light breeze | -0.8 | 29.67 | clouded over, m., snow. |
| "7 | W. | gent breeze | -14.4 | 29.96 | blue sky, detached clouds, m. |
| "8 | W.S.W. | light air | -21.2 | 30.14 | blue sky, m. |
| "29 | W.N.W. | light air | -18.9 | 30.19 | blue sky. |
| "30 | NW. by W. | light air | -13.5 | 30.17 | clouded over, m. |
| "31 | NW. by W. | gent breeze | -4.4 | 29.35 | clouded over, snow. |
| Feb. 1 | W. | light breeze | -11.7 | 29.27 | cloudy, blue sky, m. |
| "2 | W. | light air | -25.1 | 29.62 | blue sky, detached clouds, m. |
These extracts are instructive. It will be seen that on the 3d of January, when the sun had been absent some weeks, it was calm, the thermometer stood at 26° below zero (the - or minus mark before the figures indicates that), and the barometer at 29.62, with blue sky, somewhat misty or hazy—(the letter “m.” standing for misty or hazy)—a state of the air which existed most of the time when it did not snow or rain, and therefore is of no importance in this connection. The next day the thermometer began to rise, and the barometer to fall. On the 5th it clouded over, and the thermometer rose rapidly, and on the 6th it had risen more than 25°, and snow fell. On the 7th it cleared off, the thermometer fell rapidly, and the barometer rose. On the 8th the thermometer had fallen to 21° below zero, and the barometer had risen to 30.14. Another instance, in all respects similar, occurred the latter part of the month. We shall see hereafter that these changes are precisely like those which occur with us, and every where. That, as in the polar regions, and whether the sun be present or absent, or obscured by clouds, and by night as well as by day, the changes from warm to cold and from cold to warm are sudden and great, and that the latter are connected with the fall of rain and snow—that every where in winter it moderates to storm.
Many other instructive instances, especially in relation to the great difference in the seasons in our own country, and upon the same parallels elsewhere, might be cited if it were necessary. But they will more appropriately appear in the sequel.
Fig. 1.
In the above cut the isothermal lines are Centigrade. The zero of the Centigrade thermometer is the freezing point of water, or 32° of Fahrenheit. The boiling point of water is 100° Centigrade, or 212° Fahrenheit. A degree of Centigrade is equal to one degree and four-fifths, Fahrenheit. The 0° line of the cut, therefore, is 32° of Fahrenheit—the line of 5° above is 41° Fahrenheit—the line of 5° below is 23° Fahrenheit, and so on. The reader, who is not familiar with the difference in the scale of the thermometer, is desired to remember this; for we shall make occasional extracts in which the temperature is given in the Centigrade scale.
The cause of those irregularities, especially in the same seasons of different years, and when very great, is often sought and supposed to be found in the presence or absence of spots on the sun, ice floes and bergs in the Atlantic, etc., etc. But neither the spots, nor ice, nor other local causes produce them. The cause will be found in the character of the arrangements we are considering, and the irregular action of the power which controls them.
Nor is the temperature of the northern hemisphere, north of the tropics, equal in the same latitudes. Very great diversities exist in the “annual mean” as well as the “mean” of the different seasons. Accurate observations at many points have enabled men of science to demonstrate this by drawing isothermal lines (i. e., lines of equal average annual heat) from point to point around the earth, which show at a glance these differences. The annexed cut is a polar projection of the isothermal lines of the northern hemisphere, as far down as the tropic, copied from Kaemtz’s Meteorology. The dotted lines show the parallels of latitude, the dark lines the isothermal lines, or lines of equal annual average temperature. The reader is desired to observe how rarely they correspond with the parallels of latitude, and how they fall below in a few instances, and in others with great uniformity rise almost to the pole.