Previous to 1900 there was no instrument which would give through a long tube normal vision and a correct idea as to distance. At this time I took up with various opticians the question of producing such an instrument. They all contended that it was impossible to produce an instrument that would give through a long tube a field of vision equal to the natural eye or that would convey a correct idea as to the distance of an object when viewed through a long tube. The camera lucida which Mr. Holland and others had used in the earlier submarines simply threw a picture of the object on a bit of white paper, usually located on a table. This did not give to the observer any more idea of the correct distance of an object than a photograph would. Believing, however, that a solution could be found, I then purchased a variety of lenses and started making experiments. Without any special knowledge of optical science, one day quite by accident I secured the desired result and found that it was possible to secure practically normal vision through a tube of considerable length. About the same time, Sir Howard Grubb, of England, brought out an instrument in which he accomplished the same result. I then continued in my experimental work and brought out an instrument which was designed to give a simultaneous view of the entire horizon. This instrument was called an "omniscope." It was first called a "skalomniscope," which was a word coined with the idea of describing the function of the instrument and which, translated, means "to view and measure everything." A scale was used in connection with this instrument which would convert it into a range finder by measuring the image of an abject of known dimensions, such as the length of a ship or the height of its smokestack, and give simultaneous reading as to its distance. For a time it was necessary for us to manufacture our own sighting instruments, but later, when the optical houses understood the principle of the periscope, they took up the matter of manufacture and have so greatly improved them that it is now possible to secure instruments of great accuracy and fine definition. The periscope, however, is faulty, in that it is only an instrument for day use. As soon as dusk comes on the periscope becomes useless. The passing of the image down the tube and through the various lenses and prisms reduces the brilliancy of the image to such an extent that, even though it is finally magnified to above normal, the image is so thin at night that it cannot be seen. This forces the submarine to become vulnerable in making an attack at night, as it is necessary for the conning tower to be brought a sufficient distance above the surface of the water to permit the commanding officer to secure natural vision. With the powerful searchlights and rapid-fire guns, the submarine would have little opportunity to approach a surface war vessel at night without great danger of being discovered and destroyed.