ON THE HISTORY OF HTDRAUIICS AND PNEUMATICS. 365 



though they agree sufficiently well with the experiments, have not always 

 been reduced to the simplest and most convenient forms ; nor have they been 

 much improved either by Langsdorf or Eytelwein in Germany, or by Robi- 

 son in this country, who have gone over nearly the same ground with each 

 other, and have shown the way in which the results of Buat's investigations 

 may be applied to a variety of cases, which occur in hydraulic architec- 

 ture. 



One of the latest inventions, which require to be mentioned in speaking of 

 the history of pneumatics, is that of the aerostatic globe or air balloon. 

 The suggestions of Lohmeier, of Albertus, and of Wilkins, respecting the 

 various modes of passing through the air, had long remained disregarded as 

 idle speculations; and Rosnier, who, in the l/th century, descended ob- 

 liquely over some houses, by means of wings, was wholly unable to employ 

 them in ascending. Dr. Black had exhibited in his lectures a bladder fdled 

 with hydrogen gas, and floating in the air by means of its smaller specific 

 gravity, many years before Montgolfier conceived the idea of applying a si- 

 milar machine to the elevation of human beings into the aerial regions. It 

 was in 1783 that this project was first executed, and persons of a warm ima- 

 gination were disposed to believe that the discovery would be of great import- 

 ance to the convenience of mankind. But if we coolly consider the magni- 

 tude of the force with which the wind unavoidably impels a surface so large 

 as that of a balloon, we shall be convinced of the absolute impossibility of 

 counteracting it, in such a manner, as to direct the balloon in any course, 

 materially different from that of the wind which happens to blow. With 

 this limitation, the invention may still in some cases be capable of utility, 

 wherever we are only desirous of ascending to a great height, without re- 

 garding the place in which we are to descend : or where we wish to attain 

 only a height so moderate that the machine may be kept by ropes in the 

 situation which is desired. In France the balloon has lately been employed 

 with considerable success as a meteorological observatory ; Mr. Blot and Mr. 

 Gay Lussac having ascended to a height of above four miles, for the laudable 

 purpose of ascertaining some facts relating to the constitution of tlie atmosphere, 

 and to the magnetic properties of the earth. 



