It may be well to add that astronomical telescopes show the image inverted; this is done to save the use of erecting glasses which absorb light, and consequently make the image faint. If you wish to make yours useful for terrestrial purposes, you must insert in front of the field lens, and about four inches from it, a lens of the same focal length; this will turn the image right way up. The blurring of the image is sometimes caused by the two lenses composing the eye-piece not being at the distance apart proper for their focal lengths.
CHAPTER XL.—The Kaleidoscope, and How to Make it.
By W. J. Gordon.
The kaleidoscope is the most successful scientific toy of modern times. Immediately after its patenting by Sir David Brewster over three hundred thousand were sold in three months. Essentially it consists of a couple of mirrors arranged at an angle forming some even sub-multiple of three hundred and sixty. The angle usually chosen is the sixth, or sixty degrees.
Before proceeding to make a kaleidoscope for home use, it would be well to try a few experiments with two common pieces of looking-glass. Arrange them as in the diagram ([Fig. 1]), and placing an object at A, or standing them on a piece of colour work, notice the beautiful geometrical pattern formed by the various reflectors. Having experimented with various articles at the angle given, try the effect at another angle, and note how the slightest change affects the design.
Having grasped the general principle you can proceed to make one of the commoner varieties of the instrument as usually sold. These have three mirrors.
Fig. 1.
Fig. 2.