The Optical Magic Lantern Journal (July 1890)

12 The Optical Magic Lantern Journal and Photographic Enlarger. There are several methods of toning slides, but I have not tried any of them, for I much prefer the rich brown, or even the black tone of the ordinary photograph, to the red or other tints that may be obtained by toning : and I believe there is considerable risk of a toned slide fading away. When the film is thoroughly dry it is ready for: mounting for the lantern. I am sorry to say there is often very little care exercised with this part of the | work. and many an otherwise good slide is completely spoiled by the careless and slovenly way in which it is mounted. The photograph and cover glasses should be absolutely clean. and free from all dust and finger marks. And here } would say a word as to the thickness of the cover glasses. Very thick glass adds much to the weight of the slide, as you will find to your cost if you have them to carry far. The extra chin covers are the Nicest: but unfortunately they soon break when using the slides ; even the pressure of the fingers will do this. Therefore I would say use a medium thickness of | glass. and take care to have it free from scratches and air-bubbles. The paper mask to be placed between the photograph and the cover glass should be of suitable shape, and carefully adjusted to the size of the photograph; on ~ no account . se the circular masks. as this shape is most inartistic, and frequently quite spoils the picture. The masks havin one white side and the other coloured are the best, as the white side is an indication to the lantern operator as to the side of the photograph to be placed next the light, and it also enables the name of the slide to be written upon it. The binding strips should be neatly put round the : edges of the slide and two white or coloured discs placed on the two top corners of the front of the slide, to show ata glance which is the top ofthe view. Then. carefully remove all finger and gum marks, and the slide is complete. GODFREY BINGLEY. Experiments with the Optical Lantern. (Continued from page 6.) THE demonstrations in spectrum analysis and the decomposition of light are almost endless ; these we must leave for your own experiments. Removing the slit, and replacing it by a plate with a small hole in, we get a small beam of light, with which immense numbers of experiments may be made. We will show you the vibrations of a sheet of paper pasted on the end of a | tube, these vibrations being shown by a tiny mirror of , thin microscope glass silvered, which reflects the ; beams. Similar experiments may be made with tuning forks, vibrating rods, &c. Before leaving the simple adaptations, we will show ; you the geometric pen on the screen. It is arranged , as an ordinary slide, and the patterns which can be obtained are endless. These are not only pretty in themselves, but are useful in the lantern kaleidoscope, which we shall show you, and also for the production of diffraction spectra, a subject hardly suited for | demonstrations in a large room. If we remove the | ‘objective and put in its place a box which has a hole | in it, opposite the condenser. fixing the objective in this box as nearly opposite the opening as possible, we get a picture of any solid object. thrown backwards, and by turning the lantern nearly round we get the picture on the screen. ‘This is known as the aphengoscope, and with it sketches. photographs, pictures in books, watch movements, &c.,can beshown. What you have seen is only a small part of what you can yourselves easily do with a little trouble and the expenditure of a few pence on an ordinary lantern. We will now leave the simple arrangements, and turn to those which require special additions. which cannot be made by an amateur. First. we will take the lantern microscope. which is an arrangement taking the place of the objective. In this the ordinary microscope objectives and slides are used. and in the ordinary form both light and heat are concentrated that the micro slides would be destroyed if the heat were not stopped by a glass tank filled with a concentrated solution of alum. Mr. Furnivel has made for me a lantern microscope, which you see on the screen, and which has the special advantage of focussing the : heat rays and the light rays in different places. and the result is that no alum screen is needed, the slides remaining quite cool under the most intense beams of light. We will now show you the kaleidoscope, which also goes in the place of the lantern objective. the best objects for this being bits of lace, asparagus leaves, designs made with the geometric pen. and similar objects, the lace, &c.. being cemented on a circular glass plate which fits into a chromotrope frame. We expected the pleasure of the assistance of Dr. Sidebottom, of Hyde, to give us a demonstration on polarized light, but he is not well enough to come. In one respect this is fortunate. as we hope to be able to persuade him next session to give us one evening devoted entirely to polarized light, a subject he has made peculiarly his own. When light is reflected at a certain angle, or passed throurh certain substances, ‘it is split up into two parts, which have each very | Curious properties. The effect of this we will show you on the screen by passing it through various objects. I will not attempt any explanation, as the subject is too great to be treated. in a cursory manner, and we must hope for a future.and more perfect demonstra ; tion by Dr. Sidebottom, if we can get him next | session. I may conclude with again saying our object to-night is to give information, and that any questions will be answered, and the apparatus used, which is almost ‘entirely made by Mr. Furnivel, is open to your inspection, and that any information or facilities for copying any or all of the apparatus will be given either by Mr. Furnivel or myself. THOS. FLETCHER. 10; Enlargements. (American Journal of Photography.) IT is much more desirable to have large pictures than it is to make them, and if it is practicable to make small original negatives, and obtain enlargements from them which shall be as sharp and full of detail as the prints from the original negatives, much labour and trouble in the field would be avoided. In order to consider the question of the value of an