396 Miscellanies. 



The vise of wings filled with gas, proposed by M. Chabrier, appears 

 impracticable, because the swiftness necessary to produce continued 

 motion by Happing, could not be given them. It appears that a man 

 supported by an aerostat, (balloon,) would act upon the air in a much 

 more advantageous manner, in turning wheels rapidly around with 

 oblique sails, arranged like those of a wind mill. AL Navier, author 

 of this report, has subjected this motion to calculation. It is evident, 

 that supposing the apparatus placed in a perfectly calm atmosphere, 

 a very small force only would be required; but the requisite force, 

 which is in proportion to the cube of the swiftness, would rapidly in- 

 crease with the motion impressed. The question then consists in 

 finding what velocity, an apparatus suspended to a balloon, might ac- 

 quire by the strength of a given number of men* The result of the 

 calculation, in which the aerostat is supposed to be spherical, is that 

 the velocity in question increases proportionally to the power | of 

 the radius of the aerostat; and if we attribute to this radius a value 

 of 10 metres, which is double of that which commonly occurs, we 

 find that the value of this velocity is about 2^ metres per second. 

 Consequently, the balloon could not be kept motionless against a wind, 

 whose swiftness is about 2^ met. per second, a very feeble motion, 

 since it is that w r hich is just enough to set a wind mill in motion. As 

 several elements which would have increased the necessary force, have 

 been neglected in the calculation, it appears, that notwithstanding the 

 advantage which might be gained by giving to the aerostat a better 

 form than that of a sphere, it may be concluded, that in the most com- 

 mon condition of the atmosphere, the apparatus will be the sport ot 

 the winds. No advantage, either, would be gained, by replacing the 

 strength of man, by that of steam, or of compressed air. Man is 

 still the mechanical agent, w r hich, under an equal weight, is capable 

 of producing the greatest possible continued labor. We therefore 

 think, says M. Navier, that the creation of the art of navigating the 

 air, in such a manner as to be really useful, depends upon the discov- 

 ery of some new motive power, whose action would be adapted to an 

 apparatus much lighter than any of the known powers. 



It does not appear that the views of M. Chabrier, present any 

 scheme, likely to attain the desired object. — Rev* Encyc. Sep. 1830. 



Formation of Hail 







Professor 



m . jow, has attempted to verify by experiment, 



the objections of Bellain against the theory of Volta, and especially to 

 explain the influence of evaporation on the temperature of liquids. 

 He employs for this purpose a thermometer whose tube is bent up- 

 wards at the base. The ball (which of course ascends} is indented at 



