708

UNITED STATES COAST AND GEODETIC SURVEY.

photo théodolites and other photogrammeters, to corne upon a great number of types in which the many difficultés hâve been overcome, more or less successfully, by various devices.

We may flnd: A large-sized théodolite with a small caméra, placed centrally between the Y supports, after removal of the telescope from the latter, both being interchangeable;

A large caméra mounted upon the horizontal circle with a telescope and vertical circle attached eccentrically (at either side of the caméra);

A large centrically located caméra, the lens of which serves at the same time as objective of

the telescope, the correspond-ing eyepiece being at the een-ter of the frame that ordinarily supports the ground glass plate (in this form the caméra itself is the telescope) ;

Instruments where the board of the plane table has been replaced by a surveying caméra, the upper face of which receives and supports the plane-table sheet and plane-table alidade; also various other combinations (some with compass attachments).

This class of instruments has been in use for large scale surveys and where the instrumental outfit could readily be brought very near the stations to be occupied by convenient means of transportation, the instruments rarely being sub-jected to such primitive and rough methods of transportation over long distantes, as it generally has been the case on our continent when surveying caméras hâve been used.

(1) The new Italian photo-theodolite, devised by L. P. Paganini. — Paganini’s model of 1884 has been described in Appendix No. 3, United States Ooast and Geodetic Siîrvey Report for 1893.

The following description of Paganini’s new phofcotheod-olite, model of 1890, has been extracted from L. P. Paganini’s “Nuovi appunti di fototopograûa,” Roma, 1894:

The general form and the dimensions of the caméra box of Paganini’s new phototheodolite remâin about the same as with the older model, the principal change resting in the omission of the eccentric telescope which has been replaced by the centrally mounted caméra, which may, at will of the observer, be converted into a telescope. ,

The télescopes which we generally flnd attached to surveying instruments consist of a tube, slightly conical in shape, having a positive lens or a System of convergent lenses at one end (the “objective”) which produce within the telescope a real and inverted image—the same as the caméra lens—of any object toward which the lens may be directed. The other, smaller end of

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