. The art of projecting. A manual of experimentation in physics, chemistry, and natural history, with the porte lumière and magic lantern. his double line of light. //. Overtone. If the fork be struck about midway ofits length, a much higher sound will be heard alongwith the fundamental. Let the mirror be turning whenthe fork is struck, and the large sinuous line seen be-fore will now be seen covered with ripples due to theovertone. III. Interference. In the place of the mirror at m,place the second fork so that the beam of light fromthe first will fall upon it, and be reflected to the middleo
. The art of projecting. A manual of experimentation in physics, chemistry, and natural history, with the porte lumière and magic lantern. his double line of light. //. Overtone. If the fork be struck about midway ofits length, a much higher sound will be heard alongwith the fundamental. Let the mirror be turning whenthe fork is struck, and the large sinuous line seen be-fore will now be seen covered with ripples due to theovertone. III. Interference. In the place of the mirror at m,place the second fork so that the beam of light fromthe first will fall upon it, and be reflected to the middleof the screen, having both forks to vibrate perpendicu-larly. Now load the shorter fork with slides until it isnearly in unison with the long fork. When they areboth made to vibrate, the line of light upon the screenwill be seen to lengthen and shorten with regularity;at the same time beats will be heard corresponding withthe lengthening of the line. These beats may be madeto vary in frequency by moving the slides. If the beatsare as many as five or six a second, or more, and thesecond fork be swung upon its vertical axis, the inter-. rig. 4J. ference may be noted (Fig. 49); the swellings corres-ponding to the periods of coincidence, and the con-traction to the periods of interference. If the forks are now brought to unison and struck,the resultant figure will depend upon their relativephases. If they have like phases, so that each onereaches its limit at the same instant, the line of lightupon the screen will be much elongated, the amplitude 72 THE ART OF PROJECTING. being equal to the sum of the two amplitudes. If theirphases are opposite, so that one reaches its upper limitat the same instant that the other reaches its lowerlimit, then the spot of light will not be drawn out into aline at all, but will remain quiescent. These variousrelative vibrations can only be obtained by trial, butusually in four or five strokes one will develop such aphase as he requires. IV. Resultant
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Keywords: ., bookcentury1800, bookdecade1870, bookpublisherbosto, bookyear1877
