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POPULAR SCIENCE MONTHLY. 



would make it. The sketch presented herewith will give a fair 

 idea of the difference between reality and the general ideal, the 

 small car shown in solid lines being large enough to carry all the 

 passengers or freight that the balloon could sustain, and the one 

 in dotted lines about the size generally shown in illustrations of 

 air ships. The sketch is not above criticism, since it does not give 

 the location of the motor or any means for revolving the propel- 

 ler, but that is a peculiarity of the majority of air-ship pictures, 

 and the writer may be pardoned for following a common custom, 



Diagram showing Difference between Supposed and Actual Carrying Capaoitt 



OF Air Ships. 



especially as the object of the sketch is only to show the relation 

 between size and carrying capacity. 



That this sketch is not exaggerated can be easily shown. The 

 balloon is supposed to be one hundred and twenty feet long and 

 twenty feet in diameter, the taper at each end being forty feet. 

 From these dimensions it will be seen that the displacement is 

 about twenty-one thousand feet, and the sustaining capacity 

 about fifteen hundred pounds. Now, the first thing that any con- 

 servative engineer would admit would be that the apparatus 

 could not be constructed within this weight if the same factor of 

 safety were used as is customary in designing any ordinary struc- 

 ture ; hence, if any carrying capacity is to be obtained, the weight 

 and strength of every part must be reduced to a point not re- 

 garded as permissible in ordinary practice. Following this 

 course, we can assume the weight of the whole ship at one thou- 

 sand pounds, which would certainly be light considering its size; 

 we would then have a net carrying capacity of five hundred 

 pounds equal to, say, four men. The car is drawn four foot 

 square and six feet high, which is ample for four passengers. A 

 contemplation of the difference between the size of the balloon 

 and the car is enough to dampen the ardor of the most enthu- 

 siastic believer in the possibilities of aerial navigation. 



It may be claimed that by the use of aeroplanes the size can 



