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Suspension of Flies,

[Book [I.

and for other surgical operations. Posslbly they might be applied withsome advantage to the soft and yielding skulls of infants, in Order to pro-duce those eminences upon which (aocording to phrenologists) the habitsand character of individuals depend, as by means of them the most desira-ble organs of thought and passion might be developed, and the oppositeones depressed.

The prinoiple of atmospheric pressure has been introduced by thegreat Parent of the universe into every department of animated and in-animate nature. Not only does it perform an important part in thevegetable kingdom, but the movements of innumerable animals, on landand in water, depend upon it; while others are enabled by it to proteetthemselves from enemies, and to secure their food and their prey.There is something inexpressibly pleasing in examining even the meanestspecimens of the Creator’s workmanship, (if such an expression may beallowed) and what is singulär, the more closely we search into them, themore proofs do we meet with that the most elaborate and the most effi-cient of our devices are but rough copies of natural ones, which the loweranimals Vary and apply, according to circumstances, with inimitable dex-terity. Some of these will be noticed here; others will be more appro-priately introduced in subsequent chapters.

The feet of the common house-fly are constructed like the suckers abovenamed ; and hence these insects are enabled to run along, and even sleep,on the ceilings of our rooms, with their bodies hanging downwards.When in an inverted position they place a foot on an object, they spreadout the sole, to make it touch at every part, so as to exclude the air frombetween; and when the weight of the body tends to draw it away, thepressure of the external air retains it; until the fly, wishing to move,raises the edges by appropriate mechanism, and destroys the vacuum.

There is not a more interesting subject for the contemplation of mecha-nics than the movements of these active little beings. To behold themrunning not only along the under side of a plate of glass, but also up, andmore particularly down a vertical one, with such perfect command overtheir motions, is truly surprising. In the latter case, from the rapidity oftheir movements, and the fact that part only of their feet are in contactwith the glass at the same time, one might suppose the momentum of theirmoving bodies would carry them over the objects they intended to reach;instead of which, they dart along with a precision and facility as if impelledby volition alone. It is Strange, too, how they are enabled to producea sufficient vacuum between their tiny feet and the asperities on an ordi-nary wall or ceiling! And with what celerity it is done and undone!How wonderful and how perfect rqust be the mechanism of these naturalair-pumps ; and how harmonious must that machinery Work by which theenergy of the insect is transmitted to them ! Their movements when onthe wing present another source of pleasing research. Let any ingeniousperson witness, without admiration if he can, a few of them in a door-wayopen to the sun: one or two will be found floating in the centre, as if atrest, until disturbed by the near approach of another, when they dart uponit, either in play or in anger, and drive it away; then resuming their sta-tions, they remain as guards upon duty, tili called to eject other intruders.In these combats they vary their movements into every imaginable direc-tion ; they trace in the air every angle and every curve, and change themwith the velocity of thought. As they are not furnished (like most fishesand birds) with rudders in their tails, to assist in thus changing their posi-tions, but effect it by modifying the action of their wings, how energeticmust be the force that works these ! And what perfect command must