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UNITED STATES COAST AND GEODETIC SURVEY.

These leather sacks hâve métal slat arrangements, and the transfer of the plate from the sack to the caméra is made by hooking the sack with its mouth to the upper edge of the rear caméra side. While holding the bag in a vertical position the slats are opened and the plate is allowed to slide from the sack mto the carrier to be exposed.

Springs are provided at the back of the caméra box to check against a sudden dropping of the plate into the métal carrier, to avoid a breaking or cracking of the plate by striking the closed lower métal slide of the plate carrier too hard. These springs also serve to press the plate, when in position for exposure in the carrier, into perfect contact with the graduated métal frame at the back of the caméra box.

By withdrawing the upper curved handle, flg. 99, at the back of the caméra, the tension of the springs may be reduced and the plate glides into position to be exposed. After exposure the lower slide is withdrawn and the plate will slip into the empty sack B, which had been hooked to the lower edge of the caméra back for this purpose, as illustrated in fig. 99.

The eccentricity of the center of gravity, by applying the weight of the sack and plate to one side of the caméra, does not affect the adjustments of the instrument sufficiently to throw the photographie plate out of the vertical plane in which the exposure should be made. This caméra théodolite is accurately balanced when no sack is attached, in which form it is used to measure the angles that may be needed to locate the caméra station (geographically, and also in the vertical sense) with reference to surrounding trigonométrie signais.

In order to convert this caméra into a théodolite (with centrally located telescope), the back of the caméra is provided with a telescopic eyepiece JE7, of a magnifying power of from 7 to 8. This eyepiece is adjusted to form a surveying telescope with the caméra lens O as objective. It is provided with cross wires or webs, and a shutter affords the means to shut out the light when the instrument is used for photographing.

The caméra lens (objective of “caméra telescope”) being movable in the vertical sense within a range of 100 millimétrés, ail objects falling within a range of ± 17° may be bisected with this telescope. The définition of points to be bisected, when above or below the caméra horizon, would be very poor if the eyepiece E were rigidly fixed in the horizontal position, but by means of the métal arms NN the eyepiece may be revolved about a horizontal axis in such a way that it will always be directed to the center of the caméra lens.

With the double anastigmat of Gorz, which produces a perfectly fiat picture (with neither spherical, chromatic, nor astigmatic aberration or distortion), a change in the focus of the eyepiece will rarely be required.

Horizontal angles may be observed directly by means of a horizontal circle of 120 millimétrés diameter, which is provided with two verniers reading to single minutes. A sériés of experimental tests has proven that horizontal angles observed between points of considérable différence in altitude may be obtained within a limit of error of 0*4'. This instrument, therefore, gives results sufficiently accurate to locate the caméra station trigonometrically with reference to surrounding fixed points of «known positions, if they are not too far distant to be defined with this low-power telescope.

Yertical angles, however, can not be obtained directly. Still, by means of a scale and vernier attached to the camera-lens slide (or front board) the change of the caméra lens from its central or normal position (that is, a value directly proportional to the tangent of the vertical angle) may be read to 0*05 millimétré. The slide motion of the front board is accomplished with a rack and pinion, and expérience has proven that the observations may be obtained within a limit of error (converted into arc measure) of 1 minute.

The three rods, designated by h in fig. 99, are each 100 millimétrés long. They serve to elevate the instrument support and the three leveling screws 8 sufficiently high above the tripod to allow full play for the leather plate holders B, when they are placed in position to reeeive the exposed plate. The tripod legs may be folded together to one-half their length.

No ground-glass plate being provided, a spécial finder has been devised correctly showing the field controlled by the plate for any position of the caméra lens. (See Zeitschrift fur’Instru-mentenkunde, October, 1895.)

(3) Photo-theodoUte for précisé worlc, by O. Ney.—This instrument has been patented in the

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