The month of June is the only month in the year which resembles a spring month in the southern countries of Europe. The weather is then generally temperate, the sky is serene, and the verdure of the country is universal and delightful. The autumn is the most agreeable season in the year in Pennsylvania. The cool evenings and mornings, which generally begin about the first week in September, are succeeded by a moderate temperature of the air during the day. This kind of weather continues with an increase of cold scarcely perceptible, till the middle of October, when the autumn is closed by rain, which sometimes falls in such quantities as to produce destructive freshes in the rivers and creeks, and sometimes descends in gentle showers, which continue, with occasional interruptions by a few fair days, for two or three weeks. These rains are the harbingers of the winter; and the Indians have long ago taught the inhabitants of Pennsylvania, that the degrees of cold during the winter, are in proportion to the quantity of rain which falls during the autumn[31]. [31] I cannot help agreeing with Mr. Kirwan, in one of his remarks upon the science of meteorology, in the preface to his estimate of the temperature of different latitudes. "This science (says he), if brought to perfection, would enable us at least to foresee those changes in the weather which we could not prevent. Great as is the distance between such knowledge and our own present attainments, we have no reason to think it above the level of the powers of the human mind. The motions of the planets must have appeared as perplexed and intricate to those who first contemplated them; yet, by persevering industry, they are now known to the utmost precision. The present is (as the great Leibnitz expresses it) in every case pregnant with the future, and the connection must be found by long and attentive observation." The influence which the perfection of this science must have upon health, agriculture, navigation, and commerce, is too obvious to be mentioned. From this account of the temperature of the air in Pennsylvania, it is evident that there are seldom more than four months in which the weather is agreeable without a fire. In winter the winds generally come from the north-west in _fair_, and from the north-east in _wet_ weather. The north-west winds are uncommonly dry as well as cold. It is in consequence of the violent action of these winds that trees have uniformly a thicker and more compact bark on their northern than on their southern exposures. Even brick houses are affected by the force and dryness of these north-west winds: hence it is much more difficult to demolish the northern than the southern walls of an old brick house. This fact was communicated to me by an eminent bricklayer in the city of Philadelphia.