9 8 



SCIENTIFIC RECREATIONS. 



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. 



In the Conservatoire des Arts in Paris a visitor will always notice a 

 number of people looking at the mirrors in the " optical " cabinets. These 



Fig. 91. A simple microscope formed with a glass balloon full of water. 



mirrors deform and distort objects in a very curious manner, and people find 

 much amusement in gazing into them till they are " moved on " by the 

 attendants. Such experiments create great interest, and a very excellent 

 substitute for these may be found in a coffee-pot or even in a large spoon, 

 and all the grotesque appearance will be seen in the polished surface. The 

 least costly apparatus will sometimes produce the most marvellous effects. 

 Look at a soap-bubble blown from the end of a straw. When the sphere 

 has a very small diameter the pellicule is colourless and transparent ; but 

 as the air enters by degrees, pressing upon all parts of the concave surface 

 equally, the bubble gets bigger as the thickness decreases, and then the 

 colours appear, feeble at first, but stronger and stronger as the thickness 



