452 ANNUAL KECORD OF SCIENCE AND INDUSTRY. 



Numerous prominent aeronauts have warmly advocated the 

 use of the hot-air balloon, the Montgolfier, and certainly 

 these do seem highly appropriate to a certain class of mete- 

 orological observations. Almost all the danger to the aero- 

 naut is presented at the moment of his descent, in conse- 

 quence of the difficulty of arresting the balloon without a 

 sudden shock, and a consequent rupture when the wind is 

 strong. Messrs. Sivel, Penaud, and others have, therefore, 

 made use of the friction of the anchor rope, which permits 

 the gradual diminution of the motion of the balloon up to 

 the moment when the anchor takes fast hold of the ground. 

 The question of directing the movements of the balloon has, 

 as for many previous years, been treated of by numerous 

 persons, but, in general, without any great advance toward 

 the desired end. It is but a step from the attempt to direct 

 the passage of the balloon to the attempt to imitate the flight 

 of birds, and in this branch of aeronautics there has been 

 witnessed a marked advance. Important memoirs on this 

 subject have been presented by Marey, Penaud, Pettigru, 

 and others. A remarkable apparatus has been constructed 

 by Grouchot for studying, by direct observation, the move- 

 ments of the wings of birds. La Aeronaute, 1875, 13. 



AERONAUTICS IN THE ARCTIC REGIONS. 



Sivel, in 1872, laid before the French Aeronautic Society 

 a proposition for an exploration of the North Polar regions 

 by means of balloons; and the idea has lately been treated 

 of by Martinet, who states that Sivel's original project was 

 the first that seemed to be worthy of serious attention, and 

 to present practicable features. Ilis idea was to make use 

 of a large balloon filled with hydrogen, and so constructed 

 as to remain for months in the air, to effect which latter de- 

 sirable object Sivel indicated the exact means in order to 

 keep the balloon at an altitude of about 2500 feet. Special 

 means were necessary to overcome the variable eflfect of so- 

 lar radiation, which, as is well known, produce variations in 

 the altitude of a balloon to the extent sometimes of more 

 than three thousand feet. Thus in the voyage of Janssen 

 on the 22d of December, 1870, they were forced to seek an 

 altitude of from nine to thirteen thousand feet, in order to 

 escape being plunged into the surface of the sea by the 



