The contributions of this country towards the science of climatology and physical geography are matters of which we Americans may justly be proud. The Espyan theory of rain is the only one which possesses all the requisites of a law of nature. Lieutenant Maury's Charts of the winds and currents are of world wide fame. Professor Coffin, of Lafayette College, Pa., has contributed to the Smithsonian Institute, a memoir on the winds of the northern hemisphere, which is a fine specimen of laborious and philosophical investigation; and we have from the pen of Lorin Blodget, of Washington, two memoirs on the climate of the United States, which may rank with the best European reports on the subject of climate.

The first of these is contained in the Patent Office Report for 1853, and is a masterly discussion of the climatic conditions requisite for the successful cultivation of the great staples of our country - wheat, maize, the vine, tobacco, cotton and sugar.

The second is just published by the authority of government at Washington, in the large quarto volume entitled, "the Army Meteorological Register for twelve years, compiled from the observations made by the officers of the Medical Department of the army at the military posts of the United States".

These and other authorities have been most skilfully discussed and investigated, and their results are presented in a tabular shape, and in charts containing the regions of equal temperature and equal rains.

No country in the world possesses such facilities as our own for such an investigation. Extending over the whole breadth of the continent from east to west, and through 25 degrees of latitude in the southern portion of the temperate zone; the broad plains, the high table lands, the long ranges of mountain and coast, give us every variety of climate that can be found in our zone.

The following statements, compiled from the Hyetal or rain map of the U. S., will no doubt interest many of your readers.

The eastern half of the United States - that portion lying south of lat 48° and east of a waving line, the mean direction of which passes through the meridian 95° west long.: a region as large as all Europe this side of Russia, and south of the Baltic - is the most equably and copiously watered portion of the world of equal extent and compactness.

The southern part of this region - comprising the States of Florida, Georgia, South Carolina, Alabama, Mississippi, and Louisiana, and the greater portions of Arkansas, Tennessee, Kentucky, and North Carolina - forms a district in which fifty inches of rain fall in a year. In the southern part of Florida and along the coast from Pensacola to New Orleans, sixty inches fall annually.

On the rest of the Atlantic seaboard, and along a tract lying on the northern and western borders of the above, is the district of from 42 to 45 inches. The whole lake country has 30 inches, and the district of 35 inches of rain lies between the two last named.

When we compare this region with the western part of Europe, we perceive that its fall of rain is twice as great. Excepting the extreme western coasts, and the regions bordering on the Pyrenees, the Alps, and the Apennines, where 30 inches of rain fall - no part of the continent has more than 25 inches; the high plains of Germany have 20 inches, and the country east of a line passing through Berlin and Vienna has from 17 to 13 inches.

These numbers are the meant of the observations of many years, and although the whole subject of climatology is so new that perfectly reliable means are not yet obtained in the majority of cases, they are sufficiently so to give confidence to the general results.

These rains are distributed throughout the seasons, with great uniformity. Along the seaboard they are almost equally divided among the four seasons. In Florida and the valley of the Lower Mississippi, the winter rains predominate. In the Upper Mississippi and the lake country, the summer rains are in excess, and the winter rains are light.

The greatest quantity of rain falls in the United States on the Pacific coast, north of lat. 40°, where it amounts to 60 inches. One-half of this falls in the winter months, and two-thirds of the remainder in the autumn. It never rains in California, nor in the western part of Utah in summer, and the summer rains are very light along the whole region of the United States west of the Rocky Mountains.

The high table lands at the base of the Rocky Mountains and the great interior basin of Utah are very scantily watered, and many parts of those regions are dreary deserts. .

The distribution of temperature forms a very interesting portion of the Report, to which I will call your attention at another time.

Valuable as these observations are, they omit one element of climate of the greatest importance to the horticulturist. He wants to know not merely how much rain falls in his district, but what is the average moisture of the atmosphere. This can readily be learned from the wet-bulb thermometer, and ought always to be taken into the account in the description of climate.

It is understood that Lieut Maury means to extend his researches over the interior of our country, as well as over the ocean. If he will include among the elements of climate - the dampness of the air as well as the fall of rain, we think he will find zealous co-operators among our intelligent horticulturists.