REPORT FOR 1897--PART II. APPENDIX NO. 10.

711

(2) Photogrammetric théodolite of Prof. 8. Finsterwaider.—This phototheodolite (manufac-tured by Max Ott (A. Ott), of Kempten, in Bavaria) was devised by Dr. Finsterwalder after many years of practical work and expérience incidental to his Alpine surveys and studies of glacial motion. Tbis expérience taught bim tbe desirability of producing a caméra compactly built, ngidly constrncted in ail îts parts, and yet baving a minimum of weight. To avoid tbe extra weigbt wben transporting a separate théodolite (witb tbe surveying caméra) for tbe trigonométrie location of tbe stations occupied witb the caméra, be provided tbe surveying caméra with tbe means for observing horizontal and vertical angles.

Professor Finsterwalder’s phototheodolite is illustrated in fig. 99. The entire outfit weighs 10 kilogrammes, wbicb weigbt is distributed as follows:

Kilogrammes.

The instrument per se.................. 2-7

Carrying case for same................ 2-4

The tripod ............................ 1*7

One dozen leather plate holders, including

the twelve plates.................... 2’5

Packing case for the latter............ 0-7

Professor Finsterwalder has used a double ana-stigmat of Gorz and later an anastigmat of Zeiss, witb a constant focal lengtb of 150 millimétrés. Witb this fôcus tbe lens will photograpb perspectively correct a plate of 160 by 200 millimétrés. Tbe plates hâve a size of 120 by 160 millimétrés and tbey command an effective horizontal fleld of 53°, enabling the observer to cover tbe complété panorama witb seven plates.

For tbe central or normal position of the objective the caméra commands an effective vertical fleld of ± 20°.

This range would often be insufficient, particularly wben photographia g mountainous terrene of an alpine cbaracter, therefore it was deemed advisable to mount tbe objective on a slide, wbicb will permit a considérable change in the vertical sense. Owing to this de-vice, objects subtending an angle of dépréssion of 35°, togetber witb otbers subtending an angle of élévation of 5°, may still be photograpbed on tbe same plate, giving a vertical control of 40° in ail.

In extreme cases, wben it sbould become désirable to pbotograpb objects subtending angles of + 35° and of —35°, or 70° in ail, Professor Finsterwalder recom-mends tbe exposure of two plates in succession, com-manding the same (identical) horizontal angle, exposing one witb the maximum élévation of tbe objective slide and tbe other witb tbe maximum dépréssion of tbe lens.

Tbus, inclined pictures are not only avoided, but tbe effective surface of tbe plate is utilized to the best advantage, and tbe weigbt of glass to be carried is reduced to tbe minimum.

In order to obtain uniformly accurate results witb tbe relatively short focal lengtb (maintaining a constant distance between tbe lens and tbe sensitive surface of

tbe plates), the plates are not inserted into plate holders (where tbe variable tbickness of tbe glass would affect tbe so-called “constant focal lengtb”), but tbey are pressed directly against a métal frame, wbicb forms tbe back of tbe caméra box, very similar to tbe arrangement described for Cap-tain Deville’s (Canadian) caméra. To do this, use bas been made of Dr. bTeuhauss’s leather plate holders, formed like a sack B, fig. 99. Tbe inner edges of the métal frame are graduated in order to locate the principal and horizon lines upon tbe négatives.

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