A careful examination of the highly interesting Army Meteorological Register, shows that the mean temperature of the spring months is an important element in the characteristics of climate. We subjoin a few extracts to illustrate this fact. "The principal lines of the Isothermal chart differ five degrees in temperature, and east of the meridian of 100° they divide distance on the meridian with great uniformity. On the Atlantic side, the range is 35° of temperature for 22° of latitude; or, excluding the lower part of the peninsula of Florida, 30° of temperature for 17° of latitude, which is very nearly a decrease of temperature of one degree for forty miles of distance northward. The same decrease is found in the Mississippi valley/'

Taking the mean temperature of the separate spring months, the mean temperature for April nearly represents the spring mean. Places having a mean temperature of 66° for May, have 55° in April, and 45° in March. The following table gives the mean temperature for March, and the increase of the mean temperature from month to month, until June.

The increase from March to April, and from April to May is nearly alike; while the increase from May to June is less - showing that the uniformity in the advance of the temperature belongs to a leas period than three months. "The period we designate as Spring, is, on the whole, too long for identification as a single quantity in the continental temperate regions of this hemisphere. The natural seasons are unequally divided in time; in truth the winter and summer being longer, and the spring and autumn shorter than ninety days. An admirable analysis of ten years observations at Albion mines, Nova Scotia, has been made by their author, Henry Poole, Esq., by which it appears that the seasons there are naturally resolved into periods of sixty-six and sixty-three days for spring and autumn, and 120 and 116 days for winter and summer. The winter minimum temperature is January 20th, or thirty days after the solstice, and the summer maximum July 22d, or thirty-one days after the solstice. The mean annual temperature is passed on May 1st, and November 1st, forty-one and forty-four days after the equinoxes respectively.

A table is given of the means and of the extreme variations of temperature for the three spring months for thirty-four years from 1820 to 1854, at Fort Columbus, near New York, Fort Gibson on the Arkansas, and Fort Snelling at the mouth of the St. Peters, on the Mississippi.

This table shows how irregular is our spring climate - how great are the oscillations of temperature - and that the greatest deviations are below and not above the mean. The extreme cold of March, 1843, was felt over the whole country. The extremes of temperature lessen as the spring advances. It is important to ascertain the districts in which the thermometer falls to the freezing point once or more in the course of a month.

"On the coast of California an examination of the minima for five years, affords but two instances of the observation of 32° in March; while, in the interior, and in Oregon, it may be anticipated several times in this month; though the lowest observed point at stations not much elevated, is 19°. In April it is never reached in California at the sea-ievel, or near it, and rarely in Oregon; at Puget's Sound, three times in six years. In May, there are no instances of its occurrence on the Pacific, except at stations elevated 2000 feet or more.

"At Fort Tuna, in the valley of the Colorado, the freezing point is never reached in spring.

"At all the stations in New Mexico, the temperature constantly falls below 32° in every month of spring, and at Fort Massachusetts and Fort Defiance, it usually does so in June.

"In Texas, there is no frost or ice in the lower Rio Grande Valley in these months, though it twice occurs at Fort Duncan, and the posts of that vicinity, in March. Perhaps a more extended series of years would give instances of severe frost in the principal portion of this valley in March, though there could be none in the following months. All the remaining portion of Texas has the occurrence of frosts in March regularly; in April for the lower districts very rarely, though they occur in half the years, or more, at the posts on the plateaux, elevated one or two thousand feet; but never in May, at any point not mountainous.

"In the principal area of the United States, eastward, the lower portion of the peninsula of Florida, below Fort Brooke, is the only portion not liable to frosts in March, in extreme years. From the year 1822, when observations were made either at that district, or so near it as to decide the point, twelve years occur in which the thermometer fell to 32°, or lower, as far south as Fort King, and, in two of these years, at least 1835 and 1843, it fell to the freezing point as far southward as Fort Brooke. In something more than half the years of the period now observed, the coast of the Gulf, and of the Atlantic to Charleston, experiences one or more instances of a temperature of 32° in this month.

"In April, the line of ice and frosts, or a temperature at or near 32°, recedes to Fort Monroe and Fort Gibson, and they are much more rare at either of these posts, than at Florida stations in March. The depressions of temperature within which they occur, are, however, frequently connected with falls of snow in the Atlantic States, and they usually affect the more elevated portions of all the States east of Alabama. In 1854, a heavy fall of snow occurred in the middle of the month in Virginia, and ice was formed in the vicinity of Charleston. Though frosts are quite frequent in this month at St. Louis, there are few instances of the formation of ice in the latitude of Fort Gibson; light hoar frosts occur in almost every year, however, and sometimes as far southward as Baton Rouge. These may occur at an air temperature of 43°, in the ordinary positions of the thermometer.

"In May, the line of ice formation rises to St. Louis, Cincinnati, Philadelphia, and New York, and, at these points, the temperature of 32° is not found in every year. Ice is formed during the first half of the month to this latitude, in the interior districts, however, quite regularly, and hoar frosts occur in the remainder, where the altitude is noticeable, and at some distance from the coast. At the close of this month, frosts disappear from all portions of the United States territory, except at the highest altitudes cultivated".