In the preceding table the number placed before the fraction represents the mean annual temperature, the numerator of the fraction, the mean winter temperature, and the denominator the mean summer temperature. Besides the more marked difference between the mean annual temperatures, there is also a very striking contrast between the opposite coasts in respect to the distribution of heat over the different seasons of the year; and it is indeed this distribution which exerts the greatest influence on our bodily feelings and on the process of vegetation. Dove[[EA]] makes the general remark, that the summer temperature of America is lower under equal degrees of latitude than that of Europe. The climate of St. Petersburgh (lat. 59° 56′), or to speak more correctly, the mean annual temperature of that city, is found on the eastern coast of America, in lat. 47° 30′, or 12° 30′ more to the south; and in like manner we find the climate of Königsberg (lat. 54° 43′) at Halifax in lat. 44° 39′. Toulouse (lat. 43° 36′) corresponds in its thermic relations to Washington.
It is very hazardous to attempt to obtain any general results respecting the distribution of heat in the United States of North America, since there are three regions to be distinguished—1, the region of the Atlantic States, east of the Alleghanys; 2, the Western States, in the wide basin between the Alleghanys and the Rocky Mountains, watered by the Mississippi, the Ohio, the Arkansas, and the Missouri; and 3, the elevated plains between the Rocky Mountains and the Coast Range of New California, through which the Oregon or Columbia river wends its course. Since the commendable establishment by John Calhoun of uninterrupted observations of temperature, made on a uniform plan, at thirty-five military stations, and reduced to diurnal, mensal, and annual means, we have attained more correct climatic views than were generally held in the time of Jefferson, Barton, and Volney. These meteorological stations extend from the point of Florida and Thompson’s Island (West Key), lat. 24° 33′, to the Council Bluffs on the Missouri; and if we reckon Fort Vancouver (lat. 45° 37′), among them, they include a space extending over forty degrees of longitude.
It cannot be affirmed that on the whole the second region has a higher mean annual temperature than the first, or Atlantic. The further advance towards the north of certain plants on the western side of the Alleghanys, depends partly on the nature of those plants and partly on the different distribution through the seasons of the year of the same annual amount of heat. The broad valley of the Mississippi enjoys, at its northern extremity, the warming influence of the Canadian lakes, and at the south, that of the Mexican Gulf-Stream. These five lakes (Lakes Superior, Michigan, Huron, Erie, and Ontario,) cover an area of 92,000 square miles. The climate is so much milder and more uniform in the vicinity of the lakes, that at Niagara, for instance (in 43° 15′ north lat.), the mean annual winter temperature is only half a degree below the freezing-point, whilst, at a distance from the lakes, in 44° 53′ north lat. at Fort Snelling, near the confluence of the river St. Peter with the Mississippi, the mean winter temperature is 15°.8 Fahr.[[EB]] At this distance from the Canadian lakes, whose surface is from five to upwards of six hundred feet above the sea’s level, whilst the bottom of Lakes Michigan and Huron is five hundred feet below it, recent observations have shown that the climate of the country possesses the actual continental character of hotter summers and colder winters. “It is proved,” says Forry, “by our thermometrical data, that the climate west of the Alleghany chain is more excessive than that on the Atlantic side.” At Fort Gibson, on the Arkansas river, which falls into the Mississippi, in lat. 35° 47′, where the mean annual temperature hardly equals that of Gibraltar, the thermometer was observed, in August, 1834, to rise to 117° Fahr. when in the shade, and without any reflected heat from the ground.
The statements so frequently advanced, although unsupported by measurements, that since the first European settlements in New England, Pennsylvania, and Virginia, the destruction of many forests on both sides of the Alleghanys, has rendered the climate more equable,—making the winters milder and the summers cooler,—are now generally discredited. No series of thermometric observations worthy of confidence extend further back in the United States than seventy-eight years. We find from the Philadelphia observations that from 1771 to 1824, the mean annual heat has hardly risen 2°.7 Fahr.;—an increase that may fairly be ascribed to the extension of the town, its greater population, and to the numerous steam-engines. This annual increase of temperature may also be owing to accident, for in the same period I find that there was an increase of the mean winter temperature of 2° Fahr.; but with this exception the seasons had all become somewhat warmer. Thirty-three years’ observations at Salem in Massachusetts show scarcely any difference, the mean of each one oscillating within 1° of Fahrenheit, about the mean of the whole number; and the winters of Salem, instead of having been rendered more mild, as conjectured, from the eradication of the forests, have become colder by 4° Fahr. during the last thirty-three years.[[EC]]
As the east coast of the United States may be compared, in equal latitudes, with the Siberian and Chinese eastern coasts of Europe, in respect to mean annual temperature, so the western coasts of Europe and America have also very justly been compared together. I will here only adduce a few instances from the western region of the Pacific, for two of which, viz., Sitka. (New Archangel,) in Russian America, and Fort George. (having the same latitudes respectively as Gottenburg and Geneva,) we are indebted to Admiral Lütke’s voyage of circumnavigation. Iluluk and Danzig are situated in about the same parallel of latitude, and although the mean temperature of Iluluk, owing to its insular climate and the cold sea current contiguous to it, is lower than that of Danzig, the winters of the former are milder than those of the Baltic city.
| 33°.3 | |||||
| Sitka | Lat. 57° 3′ | Long. | 135° 16′ W. | 44°.6 | |
| 55°.0 | |||||
| 31°.6 | |||||
| Gottenburg | Lat. 57° 41′ | Long. | 11° 59′ E. | 46°.4 | |
| 62°.4 | |||||
| 37°.8 | |||||
| Fort George | Lat. 46° 18′ | Long. | 123° 58′ W. | 50°.2 | |
| 60.°0 | |||||
| 33.°6 | |||||
| Geneva | Lat. 46° 12′ | Altitude | 1298 feet | 49°.8 | |
| 63°.5 | |||||
| 25°.0 | |||||
| Cherson | Lat. 46° 38′ | Long. | 32° 39′ E. | 53°.1 | |
| 71°.0 |
Snow is hardly ever seen on the banks of the Oregon or Columbia river, and ice on the river lasts only a few days. The lowest temperature which Mr. Ball ever observed there (in 1838) was 18°.4 Fahr.[[ED]] A cursory glance at the summer and winter temperatures given above, suffices to show that a true insular climate prevails on and near the western coasts; whilst the winter cold is less considerable than in the western part of the old continent, the summers are much cooler. This contrast is made most apparent when we compare the mouth of the Oregon with Forts Snelling and Howard, and the Council Bluffs in the interior of the Mississippi and Missouri basin, (44°–46° north lat.,) where, to speak with Buffon, we find an excessive or true continental climate,—a winter cold, which on some days is –32° or even –37° Fahr., followed by a mean summer’s heat, which rises to 69° and 71°.4 Fahr.
[19]. p. 8.—“As if America had emerged later from the chaotic covering of waters.”
The acute natural inquirer Benjamin Smith Barton, expresses himself thus accurately:[[EE]]—“I cannot but deem it a puerile supposition, unsupported by the evidence of nature, that a great part of America has probably later emerged from the bosom of the ocean than the other continents.” I have already elsewhere treated of this subject in a memoir on the primitive nations of America:[[EF]]—“The remark has been too frequently made by authors of general and well-attested merit that America was in every sense of the word a new continent. The luxuriance of vegetation, the vast mass of waters in the rivers, and the continued activity of great volcanoes, confirm the fact (say these writers,) that the still agitated and humid earth is in a condition approximating more closely to the chaotic primordial state of our planet than the old continent. Such ideas appeared to me, long before my travels in those regions, no less unphilosophical than at variance with generally acknowledged physical laws. These imaginary representations of an earlier age and a want of repose, and of the increase of dryness and inertia with the increased age of our globe, could only have been framed by those who seek to discover striking contrasts between the two hemispheres, and who do not endeavour to consider the construction of our terrestrial planet from one grand and general point of view. Are we to regard the southern as more recent than the northern part of Italy, simply because the former is almost constantly disturbed by earthquakes and volcanic eruptions? How inconsiderable, moreover, are the phenomena presented by our volcanoes and earthquakes, when compared with the convulsions of nature which the geognosist must conjecture to have occurred in the chaotic condition of our globe, when mountain masses were upheaved, solidified, or cleft asunder? Different causes must also occasion a diversity of effects in the forces of nature in parts of the earth remote from one another. The volcanoes in the new continent,” (of which I still count about twenty-eight,) “may probably have continued longer active, because the high mountain ridges on which they are erupted in rows upon long fissures are nearer to the sea, and because this vicinity appears to modify the energy of the subterranean fire, in a manner which, with few exceptions, has not yet been explained. Besides, both earthquakes and fire-erupting mountains act periodically. At present” (this I wrote forty-two years ago,) “physical disquietude and political repose prevail in the new continent, whilst in the old continent the calm repose of nature is contrasted with the dissensions of different nations. The time may however come, when this strange contrast between physical and moral forces may change its theatre of action from one quarter of the world to another. Volcanoes enjoy centuries of repose between their manifestations of activity; and the idea that in the older countries nature must be characterized by a certain repose and quietude, has no other foundation than in the mere caprice of the imagination. There exists no reason for assuming that one side of our planet is older or more recent than the other. Islands, as the Azores and many flat islands of the Pacific, which have been upheaved by volcanoes, or been gradually formed by coral animals, are indeed more recent than many plutonic formations of the European central chain. Small tracts of land, as Bohemia and Kashmeer, and many of the valleys in the moon, inclosed by a ring of mountains, may continue for a long time under the form of a sea, owing to partial inundations, and after the flowing off of these inland waters, the bottom, on which plants would gradually manifest themselves, might indeed be figuratively regarded as of more recent origin. Islands have been connected together into continental masses by upheaval, whilst other parts of the previously existing land have disappeared in consequence of the subsidence of the oscillating ground; but general submersions can, from hydrostatic laws, only be imagined as embracing simultaneously all parts of the earth. The sea cannot permanently submerge the vast lowlands of the Orinoco and the Amazon, without at the same time destroying our Baltic lands. Moreover the succession and identity of the floetz strata, and of the organic remains of plants and animals belonging to the primitive world, inclosed in those strata, show that several great depositions have occurred almost simultaneously over the whole earth.”[[EG]]
[20]. p. 8.—“The Southern Hemisphere is cooler and more humid than the Northern.”