Because the _greater friction_ of air acting upon them, opposes the progress of that part of the arrow in a greater degree than it does the other portion. The effect is, _to keep the point of the arrow forward_, and in a straight line with its opposite extremity. If the arrow were shot the reverse way from the bow, it would _turn round_, in the course of its flight, in consequence of the friction of the air, offering greater resistance to the progress of the feathered end. [Illustration: Fig. 38.--BOW AND ARROW.] [Illustration: Fig. 39.--JEW'S HARP.] 851. _Why does a Jew's harp give musical sounds?_ Because the _vibrations of the metal tongue_ are communicated to the ear. 852. _Why will not the Jew's harp produce loud sounds unless it is applied to the mouth?_ Because the vibrations are not very intense, but when it is blown upon by the breath, the air is pressed upon it, and the vibrations are thereby rendered more powerful. 853. _Why does the alteration of the arrangement of the mouth, affect the formation of the sounds?_ Because it sends the air to the tongue of the harp in _a greater or lesser degree of compression_. [Verse: "Hear, ye children, the instruction of a father, and attend to know understanding."--PROVERBS IV.] 854. _Why does the pressure applied to the handle of an air pistol propel the cork?_ Because, between the cork A and the air-tight piston C, there is a _closed chamber of air_ B. When the handle D, which moves the piston C, is rapidly pushed in, it _compresses the air_ until it is so much condensed, that it forces out the cork A. [Illustration: Fig. 40.--AIR PISTOL, OR "POP-GUN."] 855. _Why must the handle be drawn out, before the cork is placed in?_ Because otherwise a partial _vacuum_ would be formed between A and C, and there would not be sufficient air to force out the cork by the return of the piston C D. 856. _Why does water rise in a syringe when the handle is drawn out?_ Because the pressure of the air on the water outside of the syringe, forces it into the space vacated by the drawing up of the handle, and where, otherwise, a _vacuum_ would be formed. [Illustration: Fig. 41.--SYRINGE, WITH JET OF WATER.] 857. _Why does not the water run out when the syringe is raised?_ Because the pressure of the air upon the small orifice resists the weight of the water. 858. _Why does the water leak out, but not run?_ Because water has a tendency always to _move to the lowest point_, but as the air does not enter freely the water cannot escape. It therefore _drops_, as small portions of the air enter. [Verse: "Remember now thy creator in the days of thy youth."--ECCLESIASTES XI.] 859. _Why cannot the handle be pressed in, if the finger is applied to the orifice?_ Because water is not _compressible_, like air; it must therefore escape before the handle can be pressed in. Air may be forced into a much smaller compass than is natural to it; but it is impossible to _compress water_ in any great degree.