From the accounts which have been handed down to us by our ancestors, there is reason to believe that the climate of Pennsylvania has undergone a material change. Thunder and lightning are less frequent, and the cold of our winters and heat of our summers are less uniform, than they were forty or fifty years ago. Nor is this all. The springs are much colder, and the autumns more temperate than formerly, insomuch that cattle are not housed so soon by one month as they were in former years. Within the last eight years, there have been some exceptions to part of these observations. The winter of the year 1779-80, was uniformly and uncommonly cold. The river Delaware was frozen near three months during this winter, and public roads for waggons and sleighs connected the city of Philadelphia in many places with the Jersey shore. The thickness of the ice in the river near the city, was from sixteen to nineteen inches, and the depth of the frost in the ground was from four to five feet, according to the exposure of the ground, and the quality of the soil. This extraordinary depth of the frost in the earth, compared with its depth in more northern and colder countries, is occasioned by the long delay of snow, which leaves the earth without a covering during the last autumnal and the first winter months. Many plants were destroyed by the intenseness of the cold during this winter. The ears of horned cattle and the feet of hogs exposed to the air, were frost-bitten; squirrels perished in their holes, and partridges were often found dead in the neighbourhood of farm houses. The mercury in January stood for several hours at 5° below 0, in Fahrenheit's thermometer; and during the whole of this month (except on one day), it never rose in the city of Philadelphia so high as to the freezing point. The cold in the winter of the year 1783-4 was as intense, but not so steady, as it was in the winter that has been described. It differed from it materially in one particular, viz. there was a thaw in the month of January, which opened all our rivers for a few days. The summer which succeeded the winter of 1779-80, was uniformly warm. The mercury in the thermometer, during this summer, stood on one day (the 15th of August) at 95°, and fluctuated between 93°, and 80° for many weeks. The thermometer, in every reference that has been, or shall be made to it, stood in the shade in the open air.