The Optical Lantern and Cinematograph Journal (Nov 1904-Oct 1905)

Record Details:

Something wrong or inaccurate about this page? Let us Know!

Thanks for helping us continually improve the quality of the Lantern search engine for all of our users! We have millions of scanned pages, so user reports are incredibly helpful for us to identify places where we can improve and update the metadata.

Please describe the issue below, and click "Submit" to send your comments to our team! If you'd prefer, you can also send us an email to mhdl@commarts.wisc.edu with your comments.




We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.

Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.

174 THE OPTICAL LANTERN AND CINEMATOGRAPH JOURNAL. A great deal of most excellent work has been done on stereoscopic vision by Dr. Pulfrich, of Jena, and will be found in his various papers. Among other uses he has applied it to surveying work, two photographs of the same landscapes being taken, at a considerable distance apart, to increase the stereoscopic effect. (The AstronomerRoyal at the Cape has also worked on this line.) The Zeiss Stereoscopic RangeFinder also is principally due to him. One of the most beautiful uses made of Stereoscopic Vision is in astronomical work, and is described in a paper by Dr. Pulfrich, read before the Astronomical Convention at Gnttingen in 1902. Photographs of the same region of the sky are taken at a suitable interval, which may be years apart, ard viewed stereoscopically. Any stars that have moved during the interval parallel to the line joining the eyes stand out in front of the plane of the others, or retire behind that plane, and are spotted instantly and with certainty. This is the very finest stereoscopic effect that we can ever hope to get. Suppose we take two photos at a year's interval in a direction at right angles to the line of the sun's motion in space, that motion being about 35,000,000 miles per year, when we put the two in a stereoscope we get the effect of a stereoscopic base of about 70,000,000 miles, and as photos are now taken continually, we shall steadily enlarge that base year by year, and century by century. Dr. M'Kenzie Davidson has used stereoscopic vision for X-ray work. An X-ray photo of a leg, for example, is taken; the tube shifted a few centimetres to one side, and another photo taken. When the two photos are viewed in a stereoscope, instead of having a mere flat diagram, all the bones stand out in perspective, and any foreign bodies such as bullets, needles, etc., can be exactly localised. He has gone further. Two tubes, a little distance apart, are worked alternately. A vibrating shutter in front of the right eye is open when the left tube is one and vice versa. A perfect stereoscopic effect is thus obtained. Incidentally the two photos need not be equal ; one may be so bad as to give an extremely weak picture, and yet the stereoscopic effect will be perfect. In the same way a man may have one eye very defective indeed, and yet have good stereoscopic vision. It was mentioned above that an exceptionally good man will appreciate as little as 2 to 3 sees. Of course, when working with rods as described, there is a feeling that the readings may have been assisted by shadows, or in some way unconsciously "cooked." The figure is, however, confirmed by tests with the Forbes' Range-Finder. Now in this case no such chance of error can arise, as there is no question of judging by anything but stereoscopic vision, pure and simple. The instrument is fairly well known, but a few words of description may be given. The object is viewed through a prismatic binocular. In the focal plane of the object-glasses of the two sides are two absolutely similar photographs of a balloon on clear glass. The two appear as one by stereoscopic vision. If they are both at the centre of the field they appear at the same distance as an object at practically infinite distance, say, the moon. One of them can be brought towards the other by a micrometer screw, and the eyes must converge a little to still see them as one object. The balloon then appears at the same distance as an object on the landscape, on which the eyes have to converge at the same angle. By moving the screw the balloon can be made to appear to approach or recede till it appears the same distance as any particular object ; the range of the latter is then shown on the perfectly divided screw-head. With the ordiary binocular of eight magnifying power, and about 3 in. eye-distance, the range that can be taken to one or two per cent, is limited to about 120 yds., but by adding an arrangement of prisms on a base 6 ft. long, the same effect is produced as if the eyes were 6 ft. apart, and distances twenty-four times greater — say 3,000 yds. — can be taken. The pointer on the scale can be set autonomously, if one may be allowed the expression, i.e., without reference to any known distance. A reading is taken of any object at suitable but unknown distance, first with the binoculars alone, then with the based added. From these two readings an accurate setting of the pointer can be made. Very numerous trials have been made with this instrument, both in the Army and Navy and with civilians. The sailor might have been expected to have come out far better than the soldier, owing to his having to exercise his sight more, but there is no noticed difference. The common private in the Army can almost always after half-an-hour's instruction— often, indeed, after only five minutes — take a range of about 2,000 yds. accurate to 20 yds. This with a 6 ft. base and eight magnification power is equivalent to 17 ins., and in a very few hours he will be taking 3,000 yds. accurate to about 30 yds. As might be expected, some men are better than others. One or two skilled Army sergeants give very good results ; but this may in some cases be due to other marked causes — general smartness — rather than really better stereoscopic power. But there is one observer we have come across who has distinctly greater stereoscopic power than the average. The first time he saw the instrument was at Bisley. He then looked through it at a target distant some 1,140 yds., and ranged it within 2 yds. first shot. There are two of his readings that may be mentioned. A tower of Holloway College, at Egham, was