The same principle, though not the same form, is found in Nature.
There are certain tiny spiders called Gossamers, which have a curious power of floating in the air. They have been seen on the tops of lofty spires, and they are sometimes so numerous that the air is full of their floating webs, and the ground is white with those that have descended.
Their mode of ascent is this. They climb to the top of some elevated object, if it be only a grass-blade. They then pour out a tuft of long, slender threads, which shortly begin to tend upwards. As soon as the Spider feels the pull, it crawls upon the web, and sails away into the air. The duration and height of the ascent depend much on the wind and character of the atmosphere.
The web ascends because it is for the time lighter than the atmosphere. But, as it gradually becomes laden with the moisture that more or less fills the air, it becomes heavier than the atmosphere, and gently sinks to the ground.
What may be the object of these aërial voyages no one knows. They may be for the purpose of capturing minute insects, or they may be for mere amusement. But in either case they are highly instructive, as showing the principle on which the balloon was framed.
The little Gossamer Spider is shown on the left hand of the illustration, clinging to its floating web. I believe that the Gossamer is not a single species of Spider, but that there are many species which deserve the name, being able to float in the air when they are small, but losing that capacity as they increase in size and weight.
Now we come to another branch of the same subject, namely, the safe descent from a great height by means of the Parachute.
On the right hand of the illustration is the ordinary Parachute as it appears when open and closed, in either case having somewhat the appearance of a large umbrella. It is hung to the balloon in its closed state, and when detached it falls rapidly for a yard or two with startling rapidity. The pressure of the air thus forces the ribs open, and gives sufficient assistance to the atmosphere to insure a gentle fall.
On one memorable occasion, when the late Albert Smith was in the car of a balloon upwards of a mile from the ground, the balloon burst. Fortunately it burst so completely, that the silk was driven into the closely meshed netting, and formed an extemporised parachute, which took the voyagers to the earth with safety, except some rather severe bruises.
Children often amuse themselves with miniature parachutes. They take a square piece of thin paper, tie threads to the four corners, and then bring the ends together, a cork taking the place of the car. They then launch it from a high window, and should there be a favourable breeze, it is wonderful how far it will be carried before it comes to the ground.