The Alaska daily empire., 1915-05-24
HISTORY OF TBE PER-
 lscoPE

Reading of modern submarine war. fare one often notes some particular mlntion of the marine'sf dread of the f1eriscope-that symbol Of destruction which is instantaneous. that fatal warning Of the explosion which fol- lows a few seconds iater and shatters Go atoms floating fortress of sup. posed imprognabAity It is the circle of death from the which the submar- inc commander may view the whole horizon and arrange his deadly aim.
 The modern submarine, which has developed into one of the most DO. tent factors of destruction in the Eur opean war recalls the history of the periscope which is the Keynote Of submarine successes. The trench per. iscope was described by Helyellius in the seventh gentry and intended for military purposes. This instrument was called the 'polemoscope, " and in its simplest forms consisted of two mirrors with their reflecting surfaces parallel to each other and inclined at 45 degrees to the directions of the incident light These mirrors were mounted in a tube and separated a convenient distance from each other.
 From this polemoscope was deyel- oped the optical perfection and elab- orati0n Of che modern periscope, that is derived from the Greek words peri and looking around In modern submarines the tube has a length of rom 16 to 20 feet tho diam eter is from six to nine Inches while the field view is about 65 degrees, and in ordor that objects shall look their real size it Is necessary to give a magnificent of one and quarter Co one and a hah
 In the Gesselschaft. 1914. Georz peo- pie Of Berlin gave description of the periscope made by them in which three telescope systems are employed ! This telescope includes fixed eye piece and prism, so arranged that the observer looks horizontally at the ob iect. At the focus of the eyepiece are placed a scale and pointer to show .he bearing of tAe object sighted and ? ruling to allow this distance to be estimated when the size of the object 3 known. By Che aid of a subsidiary 'ystem special parts of the field can 'e further magnifed
 The field Of view of the modern ,erisoope is stiil limited and scicn- ists are working to overcome this Huicuity An improvement recently made consists of the use Of ring re- Hector which gives a view of the whole horizon at one time. The image .ormed by the ring is very distorted. put when picked up on tue surface 'i the sea 1t can be examined more perfectly by means of the ordinary op- ical system.
 The successful use of the periscope n modern submarine depends very much upon the conditions of lighting, or it is difficult to distinguish ob- ects, especially when there is 8 mist .r spray so that effective use of .eriscope requires considerable skill md training
 The continued use of this instru aent even for modern trench warfare 8 very trying to the eyes, so that de- ices have been used to throw the mage upon ground glass screen. ,ither in land warfare or from un- CT the sea 1t is absolutely necessary hat mirrors should be fixed at thc orrect angle and that there should e no doubling or distortion of the mage.
 The optical periscope, which con { ists of two telescopes, one of them eing reversed. was first introduced y Sir Howard Grubb an English op- elan. in 19Ol