=Appearance of the Earth from the Plane.=—The view from the ordinary two-seater is greatly restricted by the engine in front and by the planes to either side and below (Figs. 7, 8, and 9). By craning his neck over the side, or by looking down through an opening in the floor, the passenger has an opportunity to learn the general appearance of the subject he is later to devote his attention to photographing. Perhaps the most striking impression he receives will be that of the _flatness_ of the earth, both in the sense of absence of relief and in the sense of absence of extremes of light and shade. The absence of relief is due to the fact that at ordinary flying heights the elevations of natural objects are too small for the natural separation of the eyes to give any stereoscopic effect. The absence of extremes of light and shade is in part due to the fact that the natural surfaces of earth, grass and forest present no great range of brightness; in part to the small relative areas of the parts in shadow; in considerable part to the layer of atmospheric haze which lies as an illuminated veil between the observer and the earth at altitudes of 2000 meters and over (Figs. 10 and 11). Due to the combination of these factors the earth below presents the appearance of a delicate pastel. As the gaze is directed away from the territory directly below, the thickness of atmosphere to be pierced rapidly increases, until toward the horizon (which lies level with the observer here as on the ground) all detail is apt to be obliterated to such an extent that only on very clear days can the horizon itself be definitely found or be distinguished from low lying haze or clouds (Fig. 4). [Illustration: FIG. 7.—The view ahead.] [Illustration: FIG. 8.—The view astern.] =Airplane Instruments.=—Mounted on boards in front of the pilot and observer are various instruments to indicate the performance of engine and plane (Fig. 2). Those of interest to the photographic observer are the _compass_, the _altimeter_, the _air speed indicator_, the _inclinometers_. [Illustration: FIG. 9.—The view between the wings.] [Illustration: FIG. 10.—Appearance of the earth from a low altitude—3000 feet or less.] The _compass_ is usually a special airplane compass, with its “card” immersed in a damping liquid. Like most of the direction indicating instruments on a plane its indications are only of significance when the plane is pursuing a steady course. On turns or rapid changes of direction of any sort perturbations prevent accurate reading. The _altimeter_ is of the common aneroid barometer type. On American instruments it is usually graduated to read in 100-foot steps. While somewhat sluggish, it is quite satisfactory for all ordinary determinations of altitude in photographic work. Were primary map making to be undertaken, where the scale was determinable only from the altitude and focal length of the lens, the ordinary altimeter is hardly accurate enough.