A convex lens is fitted in the other end of the collimator, or first tube, so that the light after passing through the slit will then pass in a beam through the prism. The other tube--the one you look through--is called a _telescope_ and in this one is fitted a convex object glass and an eyepiece which magnifies the spectrum made by the prism. When a camera is used to photograph the spectrum the eyepiece is taken out of the tube of the spectroscope and a little camera is put in its place. In this way the camera and the spectroscope are combined and this helps chemists to compare the _spectra_ of different burning substances far better than they could do with the naked eye alone. To photograph the spectrum of the Sun the eyepiece of the big telescope is taken out and the end of the tube of the spectroscope with the slit in it is fitted in its place. In making a photograph of the spectrum of a star the slit is not needed, for the light of the star itself is but a mere point. In photographing the spectrum of the Sun and stars three wonderful instruments are combined, namely, the _telescope_, the _spectroscope_ and the _camera_; perhaps I should have said four wonderful instruments, for without the _brain_ of a genius using them the Sun and stars never would have given up their secrets. APPENDICES APPENDIX A According to the official _Handbook of the Boy Scouts_, if you are a Scout and want to win a merit badge for starcraft, you must (1) _Have a general knowledge of the nature of the stars and planets._ (a) By the nature of the stars and planets is meant their colors and what they are made of. Their sizes and their distances from the Earth in a general way may also be included. (b) It is easy to tell the color of both the stars and the planets by looking at them, or by looking them up in the foregoing chapters. (c) The spectroscope shows that the stars are made of metals and gases and other substances which we have on Earth. The planets are probably made of the same kinds of metals, gases and substances as those which form the Earth, but there is no way of proving this, for the planets shine by reflected light, and in this case the spectroscope is of little use. (d) The stars are known to be suns as large or larger than our Sun; while the planets are about as large as our Earth--some smaller and some larger. (e) All of the planets are within 2,800 millions of miles of the Earth, while the nearest star, except our Sun, is 25 trillions of miles from the Earth, or 8,000 times as far away. (2) _Have a general knowledge of the movements of the stars and planets._