148 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1909. 
The first quality which I mentioned is the faculty of ascending 
to the greatest possible height. The means for accomplishing this 
end are different, according to whether the machines are heavier 
or lighter than air. In the first case it is necessary to have at your 
disposal a motive power greater than that necessary to sustain and 
move the machine in a horizontal plane. It is therefore a question 
of the power of the motor. 
If, however, the air-ship is a dirigible balloon, the motor does not 
come into consideration. It is only necessary to throw off a definite 
weight of ballast, and the greater this quantity is for a given balloon 
the higher it will ascend. Besides the weight of the motor and the 
mechanism itself and the weight of the fuel and other supplies and 
of the passengers, arrangements must also be made for a supplemen- 
tary weight that can be sacrificed. It is not enough to increase the 
volume of the gas envelope in order to increase the dispensable bal- 
_last in the same proportion, for the altitude attained does not depend 
on the absolute amount of ballast thrown off but on the ratio of this 
weight to the volume of the balloon. If, for example, with a balloon 
of 1,000 cubic meters an altitude of about 2,300 meters should be 
attained by releasing 250 kilograms of ballast, to attain the same 
altitude with a balloon of 2,000 cubic meters capacity not 250 kilo- 
grams, but 500, must be thrown off. If the weight of the air-ship 
itself, the motor mechanism, the supplies, and the passengers 
increased proportionately with the volume of the gas envelope, we 
would always have the same proportion of ballast and could ascend 
no higher in one case than in the other. This, however, is not 
the fact, for large balloons can carry a larger proportion of ballast 
than small ones, and it is with these that high altitudes are most 
easily attained. The altitude is therefore to a great degree a question 
of volume. 
It may be remarked that if lighter motors for a given power are 
provided, .or greater power for a given weight—in other words, if 
the weight is reduced, there would be more dispensable weight, more 
ballast per horsepower, and, consequently, a greater capability of 
ascension. It is also evident that to attain an extreme elevation the 
weight carried should be reduced as much as possible. Thus the 
number of passengers should be reduced to a minimum and little or 
no extra material carried. By doing this, in the case of a dirigible, 
the dispensable ballast can be increased to the extent of the economy 
which has been realized in the rest of the equipment. In the case of 
an aviation machine if its total weight is diminished and, consequently, 
the expenditure of motive power necessary to sustain the machine, 
the excess power available for attaining altitudes is thereby also 
increased. To sum up, in all air-ships, of whatever kind, altitude may 
be attained with a facility corresponding to the power available for 
