Scientific amusements . Fig. 108.—The DdubleMarble. ball cannot be touched at the same time by the exteriorsof two fingers of the same hand. When we cross ourfingers, however, the normal conditions are changed, butthe instinctive interpretation remains the same, so muchsp that the frequent repetition of the experiment does not 138 MECHANICAL TOYS, ETC. confirm the first impressions. In fact, if the experimentbe frequently repeated the illusion will become less andless marked. EXPERIMENT IN SOUND—ACOUSTICS. Sound is a sensation which affects our ears ; it is pro-duced by a cause exterior to the
Scientific amusements . Fig. 108.—The DdubleMarble. ball cannot be touched at the same time by the exteriorsof two fingers of the same hand. When we cross ourfingers, however, the normal conditions are changed, butthe instinctive interpretation remains the same, so muchsp that the frequent repetition of the experiment does not 138 MECHANICAL TOYS, ETC. confirm the first impressions. In fact, if the experimentbe frequently repeated the illusion will become less andless marked. EXPERIMENT IN SOUND—ACOUSTICS. Sound is a sensation which affects our ears ; it is pro-duced by a cause exterior to the organ itself—generallyby vibration of a body. This vibration is transmitted bythe medium serving as a means of communicationbetween nerves of hearing and the object vibrating. There are three different ways of producing sound,—by percussion, when objects strike each other ; by rubbing,. 109.—Wooden Whistle, which a Lad may make for Himself. as when a bow of a violin is drawn across the strings ;and by twanging the strings of an instrument. It is easy to prove that sound is transmitted in aperceptible space of time from one place to at a distance we see a man hammering a nail,we perceive that the noise occasioned by the strikingof the object does not reach our ears until some secondsafter the moment of contact. We see the flash of acannon before we hear the sound of the discharge, andlightning before thunder. We need not give any particular experiments here save MECHANICAL TOYS, ETC. 139 6ne—the Wooden Whistle, a toy much in vogue amongstschool-boys. Take a piece of lilac or willow-wood, and cut the barkround it with a penknife in a circle. Moisten the bark,and then beat it on your knee with the handle of theknife. Then hollow out the pith, and you will havean ordinary whistle, as in a key. A, or by cutting the
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