William Temple Franklin British peace commissioners if something could be done for his father. He noted his father's steadfast defense of the Stamp Act, and hoped that the British government might award him a diplomatic post. During 1784, Temple went to London and reconciled with his father, lengthening his stay several times before returning to Paris at the end of the year. In January 1785, Temple received the first airmail in history when a letter from his father was brought across the English Channel by a hot air balloon flown by Jean-Pierre Blanchard and John Jeffries. When Benjamin Franklin relinquished his post and
Hot air balloon course) stated in the previous section. Liftoff would require a slightly greater temperature, depending on the desired rate of climb. In reality, the air contained in the envelope is not all the same temperature, as the accompanying thermal image shows, and so these calculations are based on averages. For typical atmospheric conditions (20 °C, 68 °F), a hot air balloon heated to (99 °C, 210 °F) requires about 3.91 m³ of envelope volume to lift 1 kilogram (62.5 ft³/lb). The precise amount of lift provided depends not only upon the internal temperature mentioned above, but the external temperature, altitude above