Th: Jefferson returns his thanks to mr Farrar for the No of the Boston Journal which he has been so kind as to send him. he finds in it several excellent papers and among these he is particularly pleased with mr Farrar’s ingenious proposition for determining the mean temperature of the air thro’ a given time by the vibrations of a pendulum varying in sympathy with the variations of the air. it will certainly give the mean with an accuracy to which the common method of telling a medium between the maximum and minimum of the 24. hours has no pretention. he salutes Professor Farrar with assurances of great respect and esteem.