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would slowly approach an finally reach the earth; for this would occur before so much hydrogen had transfused as to cause the balloon to collapse. The rate of leaking should be accurately ascertained before the construction was commenced. It is altogether probably that for a million dollars a balloon could be made in which people could comfortably live for many months,—long enough to read Sir Phillip Sydney's 'Arcadia,' a feat not otherwise likely to be performed.

1cβ. The air-shop with ascensional force and a mechanical motor has been made by Santos Dumont and well-discussed by Zeppelin.

1cγ. The air-ship without ascensional force but with a mechanical motor are advocated by Langley, Maxim, Bell, and others.

1cδ. The air-ship with neither ascensional force nor with a motor must be the air-ship of the future. This seems almost demonstrable. For an air-ship can never be used for the