Meteorology in its connection with agriculture / by Joseph Henry.

  • Henry, Joseph, 1797-1878.
Date:
1858
Catalogue details

Licence: Public Domain Mark

Credit: Meteorology in its connection with agriculture / by Joseph Henry. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

    33/46 (page 483)
    the North American continent. Truth, however, transcends even I the laudable feelings of pride of country ; and, in order properly to direct the policy of this great confederacy, it is necessary to be well acquainted with the theatre on which its future history is to ho enacted and by whose character it will mainly he shaped. Temperature.—Let us now consider the distribution of tempera- ture of the wide belt across the continent of North America which forms the territory of the United States. To illustrate this, especial attention is requested to the lines drawn from east to west across the small map so frequently referred to. (Plate IV.) These, it will he seen, are of three kinds: first, the black, indicating the mean or average temperature of the year ; second, the red, denoting the mean temperature of summer ; and, third, the blue, that of winter. These lines are drawn through portions of the earth’s surface having equal temperatures for the periods mentioned, and are protracted from the result of numerous observations. They do not, however, in all cases exhibit the actual temperature of the surface ; for, in order to show their relations, and render them comparable with each other and with similar lines in other parts of the world, it is necessary that the observed temperatures in elevated positions should be re- duced to that of the level of the sea ; and in the construction of this map, allowance has consequently been made for decreasing tempera- ture of one degree for every 333 feet of altitude. The map, there- fore, will present to the eye the lines along which the temperature of the air would he equal for the periods mentioned, were we to suppose the mountain ranges entirely removed and the air brought down to the level of the ocean. These lines, at a glance, exhibit remarkable curvatures, particu- larly in the western portion of the United States, indicating a great increase of temperature in this region beyond that of the eastern and middle portion. Let us first consider the black lines represent- ing the mean temperature of the year. These, and indeed all the lines, are given for each ten degrees of Fahrenheit. Too much complication would he introduced were lines drawn for intermediate degrees on so small a map, though they have been projected on a larger one from which this has been reduced. The first black line, beginning at the top of the map, is that of the mean temperature of 40°. It commences near the northern part of Nova Scotia, passes through Canada and the middle of Lake Superior, slightly diverging from parallelism with the line of 45° of latitude until about the 95th meridian, when it more rapidly curves northward and leaves the United States for the British pos- sessions at about the 103d meridian, passing out at the top of the map at the 110th. The next line of mean temperature is that of 50°. It commences a little south of Nantucket, passes almost directly west, nearly parallel to the line of the 40th degree of north latitude, to about the 95th meridian of west longitude, whence it curves more rapidly to the north, meeting the coast of the Pacific in about the48tn degree of north latitude, near Puget’s Sound. It thus exhibits the fact that the mean temperature of a point near