The Signal Corps has purchased many samples of field glasses from various manufacturers with a view of testing their suitability for the military service. These samples may be examined by officers of the army at the signal office in Washington. Among these samples there are many excellent glasses especially suitable for the military service, but the higher grades are too expensive for general issue to line organizations in large quantities. Officers desiring an especially fine field glass should inspect the samples referred to; these, however, are not for sale by the Government, but information will be supplied concerning dealers and cost. No advice or fixed rule can be stated as to what constitutes the most suitable characteristics of a field glass. No single field glass can furnish maximum results under all conditions on account of varying conditions of the atmosphere. A high-power glass is unsuitable for use at night, hazy atmosphere, or for use of a mounted man where the glass can not be rested against a firm support. A low-power glass with large object lens to permit as much light as possible is a necessary condition for use at night. The double power glass which is issued as a part of the visual signaling outfits was designed for the military service as a compromise for conflicting conditions. A brief description of the field glasses issued by the Signal Corps, together with the cost of the same, is given below. Type A: This glass is the current result of the efforts of the Signal Corps to provide a field glass that will meet the greatest variety of conditions, and insure efficient service to the greatest number of military observers. It is really two glasses in one--a _day_ glass of medium power, and a _night_ glass of low power. [Illustration: FIG. 31.--Type A. Showing the field glass and case with sling cord, shoulder straps, belt loops, and compass.] It is to be clearly understood that while this glass is considered superior for moderate ranges, it does not replace, under special conditions, for long ranges, either the porro prism glass or the telescope. When held as shown in figure 32 with the tubes drawn out about 1 inch to secure proper focus, the glass has a power of about 5.6 diameters, and a field of about 5.4 degrees. [Illustration: FIG. 32--Signal Corps field glass, Type A.]