A Trick in the Sunshine
This trick can only be done on a sunny day, for a reason which will be very evident to those who try it.
Obtain a clear glass bottle, in the cork of which stick a hooked pin. By means of a piece of thread hang a small weight from this pin within the bottle, as in [Fig. 37], and then request some one to cut the cord without drawing the cork.
Fig. 37.—Sun’s rays focused on weighted thread.
All that is necessary to do this is a magnifying glass which is placed between the bottle and the sun at the right distance to focus the rays of the latter upon the cord. In a few seconds the heat of the converging rays will burn through the thread, and the weight will fall to the bottom of the bottle. In the same way you can