orbit is an ellipse instead of a circle, while the sun occupies one of the centres or foci, the earth approaches considerably nearer the sun in one extremity of its orbit than in the other. The difference in the distances is about three millions of miles, while the mean distance, according to the late determinations, is ninety-two millions of miles. In consequence of the diminished distance of the earth from the sun at perihelion the intensity of the sun's rays is three and one-third per cent. greater than the mean intensity. At aphelion his intensity is three and one-third per cent. less than the mean. The mean tempera tained to be about 82°. The altitude of the sun varies also with the hour of the day, and the solar intensity varies accordingly. From sunrise to mid-day the intensity continually increases, and from mid-day to sunset it diminishes. The total heat of the day is the sum of all the intensities from instant to instant between sunrise and sunset. The value of this total depends both on the magnitude and, as we may express it, the number of the intensities during the day. In other words, the total amount of heat received during a day is determined both by the intensity of the solar rays and the length of the day. At the equator the length of the day is always twelve hours. In consequence of this, the total daily heat received at the equator is less than the total daily heat received at places in the northern hemisphere, where, though the solar intensity is less, the day is much longer. On the 15th of June, for instance, the diurnal intensity at the equator is 72°, while in the latitude of forty degrees it is 90.1°. At the north pole, where the day may be It is an interesting fact, and one of momentous consequences to our race, that the annual period of greatest intensity occurs during the winter of the northern hemisphere, and the period of least intensity during our summer. The effect must be to mitigate the extremes of both seasons. As the southern hemisphere experiences the refrigerating effect of diminished distance during its winter, the limits of the uncultivable and uninhabitable zone would be removed considerably further from the south pole than they are from the north pole were it not for the fact that the larger proportion of watery surface in the southern hemisphere prevents that hemisphere from accumulating or losing heat as rapidly as the broad continental surfaces of the northern hemisphere. In the course of some thousands of years, however, all this will be re-regarded as twenty-four hours long, the daily versed. The effects of such a cosmic change of climate upon the populations of the northern hemisphere must be literally of a revolutionary character. The foregoing considerations concern only the aggregate amount of heat and light received by the earth as a whole. The actual heating and illuminating effects of the sun at any particular spot on the earth's surface vary also with the angle at which the solar rays strike that spot. This angle varies with the seasons and the hours of the day. From whatever cause a variation in the altitude of the sun is produced, his heating power is always proportional to the perpendicular let fall from the sun upon the horizon. intensity on the 15th of June is 97.6°. The amount of heat received at the pole is in excess of that received at a point on the equator from May 10 to August 3-a period of eighty-five days. On the parallel of forty degrees the excess of diurnal heat extends from the 24th of April to the 20th of August-an interval of one hundred and eighteen days. These contrasts, however, it must be remarked, apply only to the upper stratum of the atmosphere. The sun's intensity at the earth's surface is materially diminished by atmospheric absorption, and this effect is peculiarly experienced by the slanting rays of the polar regions. So far we have considered the temperature Every one knows that the mid-day sun is of a locality only in its relation to astronomical less vertical in winter than in summer. There conditions. The normal astronomical temperis always some latitude, however, at which the ature is almost always disguised by numerous mid-day sun is exactly in the zenith. About perturbating influences of a local character. the 21st of June it is the tropic of Cancer. The influence of winds and moisture upon From this time the sun recedes toward the sensible, and also upon actual, temperature south, becoming vertical at the equator about has already been mentioned. There are oththe 21st of September, and reaching the tropic er local conditions, however, which exert a perof Capricorn about the 21st of December; pour-manent and more important influence. The ing his vertical rays upon that tropic at about the time when, from our increased proximity to the sun, they possess the greatest inherent intensity. The equator, being the half-way station in the annual journey of the sun from tropic to tropic and back again, enjoys a greater average verticality of the solar rays than any other parallel. The mean heat produced at the equator by the sun's influence has been ascer most efficient of these are altitude above the sea level and proximity to great bodies of water. It is well understood that the temperature falls as we ascend above the level of the ocean. The rate of diminution of temperature varies with the hour of the day, the season, and the latitude. In temperate latitudes it may be taken at one degree for every 333 feet of ascent. Lake Superior, being 627 feet higher than the Atlantic, must experience a diminution of tem- | zone are westerly. Those localities, therefore, perature of nearly two degrees. At the level of Lake Michigan, whose altitude is 587 feet, the temperature should be one and three-fourths degrees less than at the sea-level. As the mean height of the lower peninsula of Michigan is about 750 feet above the sea-level, its mean temperature is diminished two and one-fourth degrees. which lie upon the eastern shores of the oceans experience more the ameliorating influence of situation than those upon western shores. The climate of Western Europe is accordingly less subject to extremes than that of Eastern North America. Western Europe is more equable than Central and Eastern Europe; as our Pacific shores possess a less rigorous climate than our Atlantic States in the same latitudes. Of all local influences affecting climate none are more efficient or more interesting to study Were we to run a line westward from New than the relations of a locality to extensive con- York through all the places which have the tinental areas, to oceanic currents, and to large same mean winter temperature as that city, we bodies of water. The ocean is the great equal- should find that in receding from the coast it izer of temperatures. By a Providential ar- would gradually deflect southward. Toward rangement, watery surfaces absorb and radiate the centre of the continent the amount of the solar heat less rapidly than land surfaces. Con- deflection would be considerable; but in aptinental areas, consequently, become more heat-proaching the Pacific coast we should observe ed in summer and in tropical latitudes, and a very remarkable deflection toward the north. more refrigerated in winter and in arctic latitudes, than the oceanic areas in the same seasons and latitudes. These unequal temperatures affect unequally the superincumbent masses of atmospheric air. From this source arise movements of the air, which, combined with the rotation of the earth on its axis, generate trade-winds and the other prevailing winds of different regions. Prevailing winds moving over the surface of the sea set its waters in motion. Thus ocean currents are established, which, reflected northward and southward by continental shores, serve to transfer tropical warmth to the polar regions, and polar cold to the tropical regions. From these causes it happens that in tropical latitudes the open sea is cooler than the land, while in polar latitudes it is warmer than the land. In the tem- The climatic influences of vast bodies of saltperate zones the temperature of the sea ex- water, like the Atlantic and Pacific oceans, ceeds that of the land in winter, and falls below have long been understood. The effect of it in summer. Winds blowing from the sea small inland bodies of fresh-water in averting upon the land carry with them somewhat of the early autumnal frosts has also been generally retemperature of the water. At Boston, conse-marked. But, as before intimated, meteoroloquently, or at New York, or Savannah, a sea-gists do not seem to have observed, till recently, breeze exerts a cooling influence in summer and a warming one in winter. In the elevated regions of the Alleghany and Rocky mountains would, indeed, interpose the disturbing effects of increased altitude, so that our isothermal line would be abruptly deflected southward in passing both these mountainous belts, but would turn northward again to its normal position after passing them. The winter isothermal of 30° passes through New Haven in latitude 41° 18'. In Kansas this isothermal is as far south as Fort Riley (39°), whence it bends northward to beyond the latitude of Fort Laramie (42° 40′). Experiencing then a sudden southward flexure to Santa Fé (35° 30′), in crossing the Rocky Mountains, it then resumes its northward trend upon the Pacific slope, and reaches the Pacific shore only within the limits of Alaska. that great lakes, like Lake Michigan and Lake Superior, exert an influence in deflecting the isothermal lines which is quite comparable with that exerted by the great oceans themselves. The amount of equalizing influence exerted by the ocean must obviously depend on the proximity of the water, and the relative amount These lakes, in truth, are no inconsiderable of wind blowing from the water over the land. representatives of the ocean. Lake Superior The interior of large land areas, like North is 460 miles long and 160 broad, with a mean America, Europe, or Australia, must preserve depth of 988 feet. It has a superficial area of nearly the temperatures due to the common as- 32,000 square miles. The State of Massachutronomical conditions, and the capacity of the setts might stretch herself out at full length land alone to absorb and radiate solar heat. and bathe in its waters. Even then there Hence the British Islands have a more equable would be room enough for Rhode Island at her climate than Russia. The winters of New York feet and Connecticut at her head, with Verare less severe than those of St. Louis, though mont stretched along her right and New Hampthe latter is nearly two degrees further south; shire on her left. You may take all New Enand the summers are also less excessive. But gland, excepting Maine, and hide it bodily bethe direction of the prevailing wind is a circum-neath the waters of this single lake. Lake stance of the utmost importance. A location by the ocean's shore would experience extremely little of the equalizing influence of water, if the movement of the atmosphere were always from the land. Now it results from the rotation of the earth that the prevailing winds in the temperate Michigan is 360 miles long and 108 broad, with a mean depth of 900 feet and a superficial area of 20,000 square miles. You could sink in this lake the three States of New Jersey, Delaware, and Maryland. Lake Huron, with a length of 270 miles and a breadth equal to that of Lake Superior, has a mean depth of 300 feet, a su- | would bring us a very considerable increase of perficial extent equal to that of Lake Michigan, warmth. Upon the land the influence of cliand would swallow up the whole kingdom of matic changes does not extend, on the average, Denmark, including the duchies. to a greater depth than eighty feet. Beneath You may embark upon a sea-worthy steamer this we experience an increase of temperature at Chicago and travel for thirty hours without amounting to one degree for every forty-five a sight of land; and after having passed the feet of descent. According to this law the terStraits of Mackinac, and entered Lake Supe- restrial temperature at the bottom of Lake rior, you may steam for two days more without Michigan should be increased eighteen dereaching Superior City or Duluth. The voy-grees. Were there no mingling of the deep age from Buffalo to Chicago around the lakes er and shallower strata of the water this inis a thousand miles; from Buffalo to Duluth is crease would exist. This amount of heat, eleven hundred miles, or three-fifths the dis- nevertheless-with some abatement to which tance from Newfoundland to Ireland. The majesty of the tempest is little less on the lakes than on the Atlantic, and the low perpetual moan of the breaking waves along the beach transports the imaginative listener to Long Branch or Nahant. During a summer day they breathe, like the ocean, a cooling atmosphere on every shore, while at night the direction of the breeze is frequently reversed. These are our interior land and sea breezes. To complete the analogy our great inland seas exhibit the fluctuations of a diminutive but genuine lunar tide. it is not necessary to refer-distributed through the entire depth of the water, must produce no inconsiderable elevation of temperature in the general mass. During the winter, therefore, Lake Michigan may be regarded as a great natural stove holding and slowly radiating the heat absorbed during summer from the solar fires, eked out by an unfailing accession of heat from beneath yielded by the reservoir of igneous force imprisoned within the earth. When, on a stinging wintry morning, we behold the steam ascending from the whole surface of the placid lake, we witness an analogy to the vessel of water steaming over our household fires, which is more literal and more striking than we had dared to imagine. tinents, rescuing broad areas from the waste supremacy of summer heats and wintry frosts, seem like interpositions of Providence to adapt the world to the bodily necessities of its inhabitants. Such beneficent equalizers are all great lakes; and such, not less strikingly, are those vast seas strewn through the midst of the lands which were the home of the earliest rep the Black, and Caspian seas. It is impossible that such enormous masses of water should be materially elevated above the mean temperature of the year by three months of summer weather, or depressed materially below it by three months of winter. Such vast and efficient compensators of cliThe land surfaces in the same latitudes at-matic extremes, situated in the interior of contain far greater extremes of cold and heat than the lakes. Two reasons exist for this: First, watery surfaces absorb and radiate more slowly; and secondly, the continued stirring of the waters by the winds mixes the surface temperature through a depth of several hundred feet, while, on the land, the entire effect is confined to a superficial zone of about seventy to ninety feet. The normal mean annual temper-resentatives of our race-the Mediterranean, ature of the land in the neighborhood of Milwaukee is 44°, and this should be about the mean temperature of the water of Lake Michigan. In summer the Milwaukee mean rises to 67°, while in winter it sinks to 22°. The water of the lake, meanwhile, rises in summer only to 46°, and sinks in winter only to 40°. Winds from the lake, therefore, partaking largely of the temperature of the water, must exert a material influence in equalizing the land temperatures of summer and winter. Still more, in cases of extreme weather, when the land temperature rises to 95° or sinks to 30° below zero, must the ameliorating influence of such a vast body of water, holding itself steadily at a somewhat uniform temperature, be most conspicuously and most beneficently experienced. It will interest the reader to understand more definitely and more in detail what is the precise effect of our great lakes upon the climate of the regions contiguous to them. With the view of furnishing these details we have constructed a series of isothermal charts, two of which are here reproduced on a diminished scale. These charts have recently been constructed from a new and original discussion of meteorological data, most of which have never heretofore been employed in any such attempt. For the purpose of exhibiting the climatic effects of the great lakes in a striking light we have selected for presentation the charts of isothermals for January and July. These being generally the coldest and warmest months of the year, the contrasts between the land and water temperatures are greater during those months than at any other periods. The isothermal lines, therefore, must suffer in January and July the greatest deflections from their general course. There is one cause of the mild temperature of deep lake waters during the cold season, which, probably, has been very little considered. Lakes Michigan and Superior are nearly a thousand feet in depth. They reach down toward the internal fires a distance which, if Turning our attention first to the chart of measured through the solid crust of the earth, isothermals for July, we witness a series of 1 lines drawn through localities of equal mean nental conditions. The first thing which im presses us is the extreme southward deflection of all the lines in the vicinity of Lake Michigan, and a similar, though less abrupt, deflection in This summer, which conditions the growth and health of most of our perennial exotics, as peaches, apples, and grapes. Glancing at the chart of January isothermals, the eye is first arrested by the general northward deflection of the lines in the vicinity of Lakes Michigan and Huron. direction is the reverse of the July inflection. The isothermal of 23°, for instance, which passes through Peoria, Illinois, enters the southern extremity of Lake Michigan and passes directly to Northport, at the mouth of Grand Traverse Bay. It thence sweeps southward to Lansing, when it returns northward, under the influence of Lake Huron, to Thunder Bay Island, and finally bends eastward, passing forty miles south of Penetanguishene, in Canada. the vicinity of Lake Huron. Tracing, for in- | ity of our winter climate, rather than that of stance, the line of 70°, we find it entering the limits of the chart on the 48th parallel of latitude. Its course is southeast as far as Fort Ripley, in Minnesota, whence it passes nearly eastward to the valley of the Menomonee River. Here it comes under the decided influence of Lake Michigan, and rapidly bends southward, passing through Green Bay and Milwaukee, in Wisconsin. Reappearing at Grand Haven, in the lower peninsula of Michigan, it trends almost directly northward to Traverse City, whence it arches across the peninsula till, coming within the influence of Lake Huron, it bends southward again and passes into Canada near the southern extremity of that lake. It passes thence in a northeasterly direction to Penetanguishene, on Georgian Bay. This isothermal is deflected, through the influence of the lakes, to the extent of five degrees of latitude, or 350 miles in a straight line. The general course of all the isothermals from 67° to 75° is extremely similar to that just traced. It follows, from these indications, that an almost identical July temperature stretches along the two shores of Lake Michigan from Chicago to Mackinac. It appears, however, that the immediate western shore is somewhat more cooled than the immediate eastern. This results, as a careful investigation has shown, from a slight preponderance of winds, in July, from points east of the meridian. At Chicago this preponderance is as 60 to 33; at Milwaukee, as 48 to 37. But at Milwaukee and northward, northerly and even northwesterly winds feel the influence of Green Bay. Further inspection of these isothermals discloses the fact that the July temperature of the lower peninsula of Michigan is about the same as that of the interior of Wisconsin in the same latitudes; but the heat of the Mackinac region is considerably less than that of Wisconsin and Minnesota on the same parallels. This accounts for the popularity of Mackinac as a place of healthful summer resort. On the contrary, the heat of the central and southern portions of the peninsula is equal to that experienced through the northern half of the States of Indiana and Ohio, two or three degrees further south. The July temperature of Marietta, Ohio, is 734°, which is the same as that of Flint, and less than that of Grand Rapids, Michigan. Similarly, the isotherm of 27° sweeps from Southwestern Michigan through Springfield, Illinois, and thence to Fort Riley, in Kansas, near the latitude of 39°. Eastward, the same isotherm strikes through Central Indiana and Ohio. The January climate of New Buffalo is as mild as that of Cincinnati. Traverse City corresponds in this respect with Omaha, Muscatine, Ottawa, and Aurora. Mackinac and Marquette compare with Green Bay, Fort Winnebago, and Prairie du Chien. The isotherm of 22° is deflected by the influence of Lake Michigan over a belt of four and a half degrees. This is more than 300 miles in a straight line, and is equal to the distance from Mackinac to Fort Wayne. Another fact strikingly exhibited is the difference between the January temperatures along the opposite sides of Lake Michigan. The mean at Chicago is 22°, while that of New Buffalo, directly opposite, is 30°. The mean of Milwaukee is 2040, while that of its vis-à-vis, Grand Haven, is 25°. The mean of Green Bay is 19°, and that of Appleton 15°, while that of Traverse City is 22°. Greatly as the January climate along the western shore is ameliorated by the influence of the lake, that along the eastern shore is still further ameliorated to the extent of four to seven degrees. This contrast results from the prevailing direction of the cold winds, which, in the Northwestern States, is from the west and southwest. A careful investigation of the data accumulated by observations, aggregating eleven years at Chicago, shows that, in January, the winds from the west of the meridian are to those from the east as 72 to 5. At Milwaukee, for thirteen 60 to 18. At Manitowoc, for eleven years, the westerly winds are to the easterly as 67 to 11. These results embody all January winds except those directly from the north or south. Another effect of the perturbating influence of the lakes, reacting upon topographical and continental relations, is to cause certain iso-years, the westerly winds are to the easterly as thermals to divide and, by reuniting, to inclose detached areas, which stand like islands of cold or heat. An example of the former is seen in the lower peninsula of Michigan, and one of the latter in Iowa. The greater part of Ohio, however, seems to constitute an island of uniform temperature in July, since from Cleveland to Marietta and Portsmouth the mean is not far from 731°. The distribution of the January isothermals possesses still greater interest. It is the sever At the same time the January climate along the eastern border of the lower peninsula of Michigan is not much more severe than that along the western, though the prevailing winds along the eastern shore, as in Wisconsin and Illinois, are from the west of the meridian, and carry the influence of Lake Huron away from |