The most powerful glasses are therefore to be used for minute observations on the clearest days, or where there is a strong light upon the observed object. When the light is fading, or there is little light upon the observed object, the clearer view will be had by those glasses of low magnifying power. When telescopes are fitted with a double adjusting focus, the short focus is to be used, where the light is dim, the long focus where the light is strong. Old newspapers furnish the best material with which to clean lenses. The pieces to be selected, should be free from grit or anything to scratch the glass.
Soft paper is better than chamois skin.
The telescope glasses ought to be kept scrupulously clean. If the glass is to be carried in the rain, a leather cap must always cover the eye-piece end. Without this precaution, the glass will be filled with water, and may be ruined. They are for use in observation of extensive movements, where large tracts of country must be taken in one field of view, or in sweeping the landscape in view, to find the tents of the enemy, his wagons, etc., or other objects to be afterwards more closely examined with the telescope. They are employed on ship board, or in boats, where the rolling motion interferes with the use of the telescopes.