nd, mounting once again
majestically skyward, submitted to be hauled down with all becoming
grace and ease. It is owing to their vagaries and want of manageability
that, as will be shown, "captives" are of uncertain use in war. On the
other hand, a free balloon is exempt from such disadvantages, and at
moderate heights not the smallest feeling of nausea is ever experienced.
The only unpleasant sensation, and that not of any gravity, ever
complained of, is a peculiar tension in the ears experienced in a
rapid ascent, or more often, perhaps, in a descent. The cause, which is
trivial and easily removed, should be properly understood, and cannot be
given in clearer language than that used by Professor Tyndall:--"Behind
the tympanic membrane exists a cavity--the drum of the ear--in part
crossed by a series of bones, and in part occupied by air. This cavity
communicates with the mouth by means of a duct called the Eustachian
tube. This tube is generally closed, the air space behind the tympanic
membrane being thus cut off from the external air. If, under these
circumstances, the external air becomes denser, it will press the
tympanic membrane inwards; if, on the other hand, the air on the other
side becomes rarer, while the Eustachian tube becomes closed, the
membrane will be pressed outwards. Pain is felt in both cases, and
partial deafness is experienced.... By the act of swallowing the
Eustachian tube is opened, and thus equilibrium is established between
the external and internal pressure."

Founded on physical facts more or less correct in themselves, come a
number of tales of olden days, which are at least more marvellous than
credible, the following serving as an example. The scientific truth
underlying the story is the well-known expedient of placing a shrivelled
apple under the receiver of an air pump. As the air becomes rarefied the
apple swells, smooths itself out, and presently becomes round and rosy
as it was in the summer time. It is recorded that on one occasion a
man of mature years made an ascent, accompanied by his son, and, after
reaching some height, the youth remarked on how young his father
was looking. They still continued to ascend, and the same remark was
repeated more than once. And at last, having now reached attenuated
regions, the son cried in astonishment, "Why, dad, you ought to be at
school!" The cause of this remark was that in the rarefied air all the
wrinkles had come out of the old man's fa