Popular Science Monthly/Volume 27/September 1885/Correspondence

CORRESPONDENCE.
 

AERIAL NAVIGATION.

Messrs. Editors:

SIR: The writer of the paper in the July Monthly on aërial navigation is certainly mild in his predictions of success, and still he is much too sanguine, as it seems to me. Besides the employment of a new motor, the recent French experiments have accomplished nothing not done before. If anything, they have emphasized the difficulties long recognized by aëronauts, without bestowing an iota of anything valuable toward their solution.

An enormous gas-bag is employed to encounter atmospheric resistance, and then to overcome that resistance a motive power is employed. It is the old way. One would think that effort would stop in this direction. It seems to be an infatuation similar to the "perpetual-motion" craze, just as persistent and just as hopeless.

As long as atmospheric resistance on any sort of a gas-bag is so much greater than the power developed by any known motor it is capable of carrying, the task of making a practical air-traveling machine is an impossible one.

It is the humming-bird process, and seems unfitted to man's use. Why not try the albatross or condor method, where gravity is the motive power, all active mechanism being dispensed with, and shape and position brought into prominence as the factors of success?Respectfully,

I. Lancaster.
335 Wabash Avenue
Chicago, June 29, 1885.
 

 
HOW THE LOCUST LAYS ITS EGGS.

Messrs. Editors:

Dear Sir: During the appearance of the so-called seventeen-year "locust" (Cicada septendecim) at this place in 1868, the commonly accepted account of the manner in which the female deposited her eggs in the twigs of trees included the statement that a transverse incision was made by the insect below the place where the eggs were deposited, causing the twig to break off and hang by the bark only. This was supposed to serve an important purpose in the hatching of the eggs, and was regarded as a remarkable exhibition of instinct on the part of the insect. The fact that the whole woods became brown with dead twigs seemed to give color to the statement. But, having carefully observed the process during the present appearance, it is very clear that the breaking is accidental, and disastrous to the eggs, rather than premeditated and beneficial. No incision is made, other than those in which the eggs are placed. Only a small part of the twigs break, and they without any regularity as to the place of fracture.

Another erroneous statement, which is frequently made, is that the eggs are laid in parallel furrows. The incisions in the wood are V-shaped, starting from a single small hole through the bark at the angle of the V. The furrows are sunk deeply into the hardest part of the wood, the eggs placed in the bottom, and left thickly covered with the hair-like fibers of the wood displaced in making the trench, and left attached at one end. The form of the incision seems to be due to the necessity of placing the eggs in solid wood, avoiding the pith. In a number of instances where the incision had accidentally penetrated the pith, the furrow was left incomplete, and no eggs were deposited.

As may be supposed, ovipositing is attended with great labor on the part of the female. Each thrust of the ovipositor requires a severe and prolonged struggle; each furrow, judging by the number of displaced fibers, must require from twenty-five to forty thrusts; and each female makes many separate furrows.

Charles B. Palmer.
Yellow Springs, Ohio, July 7, 1885.