The lightning bugs or fireflies which are seen so often on summer evenings in the country and among the trees in the parks of the city, are similar to the species of beetle called the glowworm in Great Britain, although the glowworm there does not give as much light as the firefly in America. In reality it is only the female which is the lightning bug, for the male is not equipped with any lighting power. He has the bad habit of going out nights, and so the female has had to make use of her ability to make part of her body shine with a sort of a phosphorus green light in order to show him the way home, very much as a dweller in a poorly-lighted street keeps a light in the window or on the porch to guide visitors or the late home-comer to the proper house. She seems to possess the power of moderating or increasing the light at will. The most brilliant fireflies are found only in the warmer regions of the world. The ordinary firefly to which we are accustomed gives off a very much brighter light if placed in warm water. Fine print may be read by the light of one kind which is found in the West Indies; in Cuba the ladies have a fashion of imprisoning them in bits of netting or lace of a fine texture and wearing them as dress ornaments, and in Hayti they are used to give light for domestic purposes, eight or ten confined in a vial emitting sufficient light to enable a person to write. The Story in the Making of a Picture[10] Let us suppose, for the purposes of explanation, that as far as _seeing_ goes, any object is made up of countless infinitesimal points of light, and that the business of the eye is to gather them in and spread them out at the back of the eye in exactly the same relation they bore to each other on the object. The points of light, so duplicated, would thus form the image of the object. The camera works very much the same way. The lens at the front of the camera is the eye, and the plate or film at the back of the camera corresponds to the back of the eye. The lens collects all the points of light of the object we wish to photograph, and directs them to the plate or film in such fashion that they occupy exactly the same relative position that they did before. An image of the object is formed. Now if we could look inside the camera and the image were visible, we would see that it was upside down. The reason for this is very simple, as the accompanying diagram shows. The ray of light from “A” at the bottom of the object passes through the lens at an angle, and continues in a straight line until interrupted by the film or plate. It started at the bottom of the object and ended at the top of the image. The position of all the points of light is just reversed, although their relative position remains the same. [Illustration: SHOWING INVERSION OF THE IMAGE] “Then here,” you say, “is where your analogy between the camera and the eye falls down.”