These observations, upon a comparison with the same parallels of latitude in the eastern states, show that there is no material difference of climate between the two sections of our country, except that produced by local causes, as mountainous districts, contiguity to the ocean, &c.
A similar error has existed in relation to sudden and extreme changes of weather in the West. People who emigrate to a new country have their curiosity awakened, and perhaps for the first time in their lives become quite observing of such changes. From habitually observing the weather the impression is produced on their minds that there is a marked difference in this climate. Dr. Rush declares that there is but one steady trait in the character of the climate of Pennsylvania—and that is, it is uniformly variable, and he asserts that he has known the thermometer fall 20° in one hour and a half. March 26-27, 1818, the thermometer in St. Louis, fell 41° in 30 hours—from 83° to 42°. I have no record or recollection of a more sudden change in 18 years. Mr. Legaux saw it fall in the vicinity of Philadelphia, 47° in 24 hours, and Dr. Drake states that this is five degrees more than any impression ever observed in Cincinnati, in the same length of time. Emigrants from New England and the northern part of New York state, must not expect to find the same climate in the West, at 38 or 40 degrees; but let them remove to the same parallel of latitude in the West, to Wisconsin, or the northern part of Illinois, and they will probably find a climate far more uniform than the land of their birth.
Prevailing winds modify and affect the climate of every country. Southwestwardly winds prevail along the Mississippi Valley. The following tabular view of observations made at Cincinnati, by Dr. D. Drake, for six succeeding years, with so few omissions, that they amount to 4200, will give further illustrations of this subject. They have been brought from eight points of the compass.
| OBSERVATIONS | |||||||||
| Months | S. E. | S. | S. W. | N. E. | N. | N. W. | E. | W. | CALM. |
| January | 6 | 2 | 13 | 8 | 1 | 21 | 3 | 6 | 6 |
| February | 5 | 1 | 13 | 8 | 1 | 14 | 0 | 5 | 8 |
| March | 10 | 1 | 16 | 11 | 1 | 10 | 0 | 5 | 4 |
| April | 7 | 0 | 24 | 10 | 1 | 8 | 1 | 3 | 5 |
| May | 7 | 1 | 19 | 10 | 0 | 10 | 1 | 4 | 6 |
| June | 9 | 1 | 23 | 12 | 5 | 7 | 1 | 2 | 3 |
| July | 6 | 1 | 19 | 11 | 2 | 11 | 1 | 4 | 4 |
| August | 6 | 1 | 23 | 10 | 1 | 12 | 1 | 1 | 6 |
| September | 6 | 1 | 23 | 9 | 0 | 8 | 2 | 3 | 3 |
| October | 9 | 1 | 24 | 6 | 1 | 10 | 2 | 4 | 3 |
| November | 9 | 3 | 13 | 6 | 1 | 10 | 2 | 7 | 5 |
| December | 7 | 1 | 11 | 5 | 0 | 15 | 2 | 6 | 9 |
| Total | 87 | 14 | 221 | 106 | 14 | 136 | 16 | 50 | 62 |
The results of my own observations, made for twelve years, with the exception of 1826, and with some irregularity, from travelling in different parts of Missouri and Illinois during the time, do not vary in any material degree from the above table, excepting fewer east and northeast winds.
Dr. Drake has given a table, setting forth the results of 4268 observations on the state of the weather at Cincinnati, from which it will be perceived that of the 365 days in a year, about 176 will be fair, 105 cloudy, and 84 variable.
Dr. L. C. Beck made similar observations at St. Louis during the year 1820, which produced the result of 245 clear days, and cloudy, including variable days, 110.
| Years. | Clear days. | Cloudy days | Variable days. |
| 1 | 180 | 107 | 68 |
| 2 | 158 | 112 | 91 |
| 3 | 187 | 78 | 85 |
| 4 | 152 | 106 | 107 |
| 5 | 185 | 111 | 68 |
| 6 | 172 | 112 | 74 |
| Total 6 years. | 1,034 | 626 | 493 |
| Mean terms. | 172.33 | 104.33 | 82.16 |
The following table shows the condition of the weather in each month of a mean year, for the above period.