One may also place a piece of money at the bottom of a basin, and then stoop down gradually, until, the edge of the basin intervening, the coin is lost to view. If an operator then fills the basin with water, the piece of money appears as though the bottom had been raised. The glass lenses used by professors may be very well replaced by a round water-bottle full of water. A candle is lighted in the darkness, and on holding the bottle between the light and a wall which acts as a screen, we see the reflected light turned upside down by means of the convergent lens we have improvised (fig. 90). A balloon of glass constitutes an excellent microscope. It must be filled with perfectly clear, limpid water, and closed by means of a cork. A piece of wire is then rolled round its neck, and one end is raised, and turned up towards the focus; viz., to support the object we wish to examine, which is magnified several diameters. If a fly, for instance, is at the end of the wire, we find it is highly magnified when seen through the glass balloon (fig. 91). By examining the insect through the water in the balloon, we can distinguish every feature of its organism, thanks to this improvised magnifier. This little apparatus may also serve to increase the intensity of a luminous focus of feeble power, such as a lighted candle. It is often employed in this manner by watchmakers. If a bottle full of water is placed on a table, and exposed to the rays of the sun, the head of a lucifer match being placed in the brightest centre of light caused by the refracted rays, the match will not fail to ignite. I have succeeded in this experiment even under an October sun, and still more readily in warm weather. [Illustration: Fig. 91.—A simple microscope formed with a glass balloon full of water.]