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UNITED STATES COAST AND GEODETIC SUR VE Y.

At e and g, fig. 113, are two stops representing the ends of the photographie field ezg, which is identieal with the horizontal angle commanded bv each plate. 1

The lever h, fig. 112, serves to locate the principal point /, fig. 113 ; when the edge of the ruler LL abuts against the upturned lever h, and the principal ray zf (bisecting the angle ezg) inay be drawn npon the plane-table sheet.

With reference to fig. 112 : b = rubber bnlb for operating the pneumatic shutter of the caméra. t = head of pinion which serves to elevate or depress the caméra lens, the change from the normal position of the lens being read on a scale with vernier. n — spirit level, two being provided (at right angles) for adjusting the instrument. R = movable plate carrier. LL = lever for moving the plate carrier R forward (toward the lens) until the sensitive surface of the plate is brought into contact with the graduated métal frame vv.

The horizon and the principal line may be located upon the perspectives by means of the centimètre graduations on the inner edges of the métal frame vv, or two fine wires may be attached to the corresponding points of the graduation.

The caméra is supported by the three leading screws s, their upper ends resting in three slots of the lower face of the caméra box. The latter is firmly united with the tripod head by means of a central clamp screw with spiral spring. T=graduated horizontal circle with clamp screw. It serves to enable the observer to turn the caméra by an equal amount in azimuth after each expos-ure. xx^=-correction screws to adjust the graduated métal frame vv to bring the principal point into the optical axis of the caméra lens.

The plane-table M, with alidade K, serves to locate the caméra station in both the vertical and horizontal sense. If the caméra stations are not very close together, the plane-table may also serve for the location of tertiary points and for the sketching of details.

This photographie plane-table is well suited for topographie reconnaissance surveys. The results obtained by means of the same may not be as précisé as those obtained with the more complieated and refined phototheodolites, but it is more easily transported, is very simple in manipulation, and the adjustments are not liable to be easily disturbed. The instrument is compact, well conceived, and excellently executed.

The size of the photographie plate is 12 by 16 centimètres, giving an effective picture within the graduated margin of 10 by 14 centimètres.

The cube shaped caméra has sides of 21 centimètres length, and weighs 3*5 kilograms. The packing case, including the entire outfit and stout tripod (three folding legs), weighs only 11*5 kilograms. The cost in Yienna of the complété instrument is 400 florins.

V. PANORAMIC CAMERAS.

The lenses of the older surveying caméras gave correct perspectives only for small angles, rarely exceeding 30°, and Martens, in Paris, was probably the first to devise a so-called panoramic caméra to photograph larger sections of the horizon on one plate, even with lenses that ordinarily would cover but a small angular field.

If the objects to be photographed are far enough distant to permit the use of a constant focal length of lens for the picture, and if the lens may berotated about a vertical axis passing through the second nodal point of the lens System, such panoramic views may be obtained upon a sensitized surface bent into a half cylinder whose radius equals the constant focal length of the lens and whose axis coincides with the vertical axis of rotation of the caméra lens.

The topographie cylindrograph of R. Moessard.—The foliowing-described apparatus has been devised by It. Moessard (commandant du Génie, attaché au service géographique de l’armée), of St. Cyr, France.

The hemicylindrical caméra box, fig. 114, rests upon a tripod, with three leveling screws to adjust the verticality of the axis of révolution aa of the caméra lens O, which axis coincides with that of the half cylinder formed by the sensitized surface of the film. The latter may be replaced by a half-cylindrical ground-glass plate.

The caméra lens O may be rotated by hand about aa, using the sight ruler 8 as lever. By viewing the landscape through the sights PP' of the lever 8, the proper timing for the exposure

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