The advance of photography : its history and modern applications (1911)

324 THE ADVANCE OF PHOTOGRAPHY viewed through the eye-piece, again magnified so that a still greater image S' R is produced. It will be seen from the figure that rays of light from r, after passing through the lens a b, converge to R. R is therefore the image of r as formed by lens a b ; similarly the light from s converges to form an image at S, and so with all points, between r and s. Again considering the rays from r, it will be seen that they diverge after passing R, and that as the result of these diverging rays passing through the lens c d it appears to the eye, behind that lens, as if these rays actually proceeded from R\ Thus $' R' is the apparent image of the object s r as seen by the eye after the light has passed through the lenses a b and c d. Camera Attachments. — Since microscopic work forms such an important ll part in biological studies, special camera attachments for microscopes are now made, as it is much more convenient to obtain a photograph of a preparation, and from this make a lantern slide, which can be projected so as to be visible at the same time to a larger number of persons than it would be possible to allow to separately view the image as formed in the microscope. Again there are instances where the object under observation is undergoing change so rapidly that it would be impossible to keep a good record of its varying appearances by any other process than the photographic. Of course direct representation of the object on the screen by micro-attachments to the lantern are to be preferred when possible, but this process reachesa practical limit when the strong light required for the Fig. 135.