314 APPENDIX. 



telescope till about ten minutes before three, when the person 

 who set it up observed it to sink very rapidly, after which it 

 was no more seen. 



At the time the balloon ascended, the mercury in the 

 barometer, 30 feet from the surface of the earth, stood at 30. 

 28. Thermometer (Farenheit) 57. Hyg. 0. 5. Wind 

 variable and very gentle: a few clouds in the sky of the 

 modification of cirrus. 



The air balloon fell at five minutes before five, the same 

 day at Wilbraham, near Cambridge. The sudden diminution 

 of the angle of its altitude, which has been called its sudden 

 descent, could not be occasioned by any rent in the balloon, 

 since it afterwards travelled nearly fifty miles. At ten 

 minutes before three it appeared in the telescope to be well 

 distended : it is therefore probable, that at that time it had 

 attained its greatest elevation. Its motion was, therefore, 

 horizontal ; and it being about twenty five miles in the hour, 

 and direct from the eye of the observer, it would, without 

 any descent of the machine, occasion a rapid alteration of the 

 angle subtended by the line of its perpendicular altitude. 

 The diminution of the angle being rapid in proportion to any 

 other observation, it was concluded that it must have been at 

 that time descending, because we could not at that moment 

 know the velocity of the current, which the time and place of 

 its descent have since proved to be very great. 



A small balloon launched the same day went uniformly in 

 the same current of air. Since the above, I have made up- 

 wards of thirty experiments with air balloons, some filled 

 with inflammable gas, and then with rarefied air. Some few of 

 them have gone uniformly with one direction, but most have 

 indicated four or five, and some seven or eight, different 

 currents of wind : the currents below, too, have several times 



