488 Professor G. E. Bryan [Feb. 8, 



an hour, being sufficient to enable tbe machine to be driven against 

 the amount of wind encountered on a fairly calm day, and the machine 

 having been steered at will and brought back to the starting-point. 

 The only previous record of a similar kind is that of Messrs. Eenard 

 and Krebs, who, in 1885, performed a journey in their balloon ' La 

 France,' and returned to the starting-point again. But the speed of 

 that balloon has been variously described by writers as four and four- 

 teen miles an hour, and, unless the latter figure is the correct one, it is 

 certain that the balloon could never hold its own against the light 

 winds blowing even in ordinary calm weather. The recent experi- 

 ments of Santos Dumont have excited considerable interest ; but we 

 have not, so far, seen any records of performances by this machine, 

 beyond the maintenance, for half a minute, of a relative speed of seven 

 miles an hour in the face of a wind blowing at four miles an hour — 

 giving for this brief interval a forward velocity of three miles an 

 hour. 



The chief advantages of the Zeppelin balloon are (1) its division 

 into seventeen compartments, and (2) the distribution of the load at 

 two points instead of at the centre. The former feature has not only 

 the advantage of minimising the danger arising from escape of gas 

 — in particular as the result of bullet shots in times of war — but, 

 what is more important, it prevents the gas from " wobbling about " 

 (for no other phrase is so expressive) in the interior, an action which 

 would cause the envelope to flap, absorbing energy, and greatly in- 

 creasing the resistance of the air. The agreement between the speed 

 actually obtained and that previously calculated from theory was 

 very close indeed. From what has been said above, the balloon, 

 which carried a load of about ten tons, must have displaced a volume 

 of air somewhere about equal to the volume of water displaced by a 

 ship of 10,000 tons, and it is not difficult from the illustrations to 

 realise that such was the case. In ignorance of this simple property, 

 many prospectuses are issued of companies for promoting air-ships, 

 quite impracticable in reality ; and a diagram was exhibited on the 

 screen of a kind of aerial tramcar, filled with passengers, supported by 

 three cigar-shaped balloons smaller than the tramcar itself. Another 

 example of want of knowledge on the part of promoters of air-ship 

 syndicates was exhibited on the screen, in the form of a design of an 

 actual patent specification, drawn up not many years ago, for seats on 

 such " aerial tramcars," containing cavities filled with gas to help 

 raise the machine. Remembering that a cubic foot of air only weighs 

 about an ounce, the lifting power would only amount to roughly about 

 an ounce per cubic foot of cavity, and the diminution of weight would 

 be far less than that obtained by making the seats of light bamboo. 

 To obtain an appreciable effect, the cavities must be filled with what 

 does not exist, namely, " something which is lighter than nothing, and 

 has a tendency upwards." 



Passing from the mechanically-propelled balloon to the question 



