Sect. VI.] Pneumatics. 53 



ment is to be expected. That part of pneu- 

 matics, also, which relates to the construction of 

 Chimneys, the comfort of human habitations, and 

 the economy of fuel, has been, in modern times, 

 the subject of much inquiry, and very useful im- 

 provement, by Dr. Desaguliers and Mr. Anderson, 

 of Great Britain, and by the illustrious Americans, 

 Franklin, count Rumford, and many others. To 

 which may be added a number, almost countless, 

 of wind instruments and machines, which modern 

 ingenuity has invented, and which have grown 

 out of our increasing knowledge of the qualities 

 and laws of the important fluid in which we are 

 immersed. 



In this period, beyond all doubt, we are to place 

 the invention of Balloons. In 1729, Bartholomew 

 Gusman, a Jesuit, of Lisbon, caused an aerostatic 

 machine, in the form of a bird, to be constructed ; 

 and made it to ascend, by means of a fire kindled 

 under it, in the presence of the king, queen, and 

 a great concourse of spectators. Unfortunately, 

 in rising, it struck against a cornice, was torn, and 

 fell to the ground. The inventor proposed renew- 

 ing his experiment ; but the people had denounced 

 him to the Inquisition as a sorcerer, and he with- 

 drew into Spain, w^here he died in an hospital. 



In 1766, the Hon. Henry Cavendish discovered 

 that inflammable air (the hydrogen gas of the 

 French nomenclaturists) was at least seven times 

 as light as common air. It soon afterwards oc- 

 curred to the celebrated Dr. Black, that if a thin 

 bag were filled with this gaseous substance, it 

 would, according to the established laws of specific 

 gravity, rise in the common atmosphcn^j but he 



