The combination of glasses which enabled me to inspect the above details may be stated briefly thus: In the place of my astronomic eyepiece, I use an elongator (obtainable of opticians) to increase the power. Into this I place my terrestrial tube, retaining only the field glasses, and using a microscopic eyepiece of seven eighths of an inch in diameter. Over this I slide a tube containing my colored glasses, one dark blue and two dark green, placed at the outer end of the sliding tube, one and a half inches from the eyeglass. The colored glasses are three quarters of an inch in diameter, and the aperture next the eye in diameter half an inch. The power which I usually employ magnifies but one hundred and fifty diameters; and I use the entire aperture of my object glass. This combination of colored glasses gives a clear dead white to the sun, the most desirable for distinct vision, as all shaded portions, such as spots, however minute, and their underlying dusky penumbra, are thus brought into strong contrasts. FOOTNOTES: [11] Imagine an immense sphere enclosed within two contiguous and equally thin envelopes, and yet sufficiently thick to show their edges distinctly when broken; the outer, a photosphere, having an intensely bright surface, and the inner, or penumbra, of a dull gray surface; while the enclosed hollow space is all dark, with the exception of an occasional fleecy cloud, floating within, and contiguous to the inner envelope. Now remove a large irregular piece from the outer, and a smaller piece from the inner envelope, and you have an exact idea of the appearance of a spot; contrasting the comparative brilliancy of the photosphere with the penumbra; their relative thickness; the intense blackness within, and occasional cloud stratum floating beneath the opening, as seen, under the most favorable circumstances, with a good telescope. FOOTNOTES: [12] The Nasmyth willow-leaf appearance, I think, is either the result of imperfect vision, defective instruments, or unfavorable state of the air, distorting the unvarying result of my observations, as above described, which have been a thousand times repeated in our clearer atmosphere, both on the coast and interior mountain regions. My observation of a general pore-like character, over the whole surface of the photosphere of the sun, is, I think, corroborated by considering the spots, as usually known and visible with ordinary instruments, as merely greater pores of the same general character. AN ARMY: ITS ORGANIZATION AND MOVEMENTS. _FOURTH PAPER_. In previous papers we have briefly related the history of the art of war as now practised, stated the functions of the principal staff departments, and mentioned some of the peculiar features of the different arms of military service. It remains to describe the operations of an army in its totality--to show the methods in which its three principal classes of operations--marching, encamping, and fighting--are performed.