This slide shows the Peoples Building of the Carl (Fig. 7) Zeiss Foundation in Jena. The ground plan was plotted from two sets of stereophotos. This Zeiss establishment is a rather socialistic affair. Once a workman is in its employ for two years he cannot be discharged for any reason unless given a sum equal to a certain number of years'

full pay. Its officials are employed for life. They also cannot be discharged, although they may leave if they wish to. Among these officials are a number of scientific co-workers of the first rank as investigators, such as, to mention only a few of the forty or more, Dr. Schott, to whom the world is indebted for the celebrated Jena glasses, known to astronomers, oculists, microscopists and chemists; Dr. Siedentoph, whose origination of the ultra microscope has made vis ble and almost measurable the ultimate atom of matter; Dr. Pulferich, who has developed these photo theodolites and related instruments and many more. This establishment justly prides itself on having proven the baselessness of the oft repeated assertion that socialistic co-operative work must lack the incentive to be found in the prospective greater gain of individualistic effort. From the Zeiss establishment has come much of the advance in its field of optics and optical apparatus and out of its portals issues the best of work, in some details unequalled work; it is but fair to the far-sighted projector of the enterprise, Dr. Abbe, who placed it on its communistic basis, to believe with him, that the inherent tendency of man to do the best work that is in him would be furthered rather than held back, by placing mankind under conditions where it could concentrate on its work rather than on the questions of next day's or next year's means of living.

You will recognize the main portion of this picture as a portrait. (Fig. 8) It was drawn by the laying down of contour lines from a set of stereo photographs, all determined by exactly the same methods in use for topographical surveying. The field here is a portrait bust of Moltke and the topographical levels differ by fractions of an inch only. A portrait bust was selected as a test specimen because it permitted of accurate measurements by other methods. No errors exceeding 1-32 in. were found. Note the profile at the side and the horizontal sections at nose and forehead levels. Dr. Pulferich showed me a portrait bust that he himself made of Mrs. Pulferich in almost life size. As I was told by others also that his lady was satisfied with it, that satisfaction would be accepted by your wives and sweethearts as fair evidence of the quality of the work. The method followed is the building up of the entire bust from profile planes and fairing these by filling in the steps. A process very similar to that followed by the builder of ships models from horizontal and transverse section contours.

A pantographic apparatus carrying milling cutters and guided by the stereophotographs is, I believe, in contemplation for portrait. sculpture. When it is out, we will all be able not only to "kodak" our nearest and dearest, but to "stereoscope" them as well.

FIG. 8.

The camera required does not differ in principle from the c stereoscopic camera; naturally it is constructed with far gr cision. To go into the details would lead us too far.

The Stereo-Comparator, however, with which the pla

plored and the survey measurements made on these plates is probably of sufficient novelty to earn me your pardon for taking up a little more of your time.

N

This slide illustrates two stereograms of a building. (Fig. 9) The horizontal line crossing both establishes the altitude base line. Some of you have your surveying days so far behind you that you may need a little freshener as to such terms as "altitude." The latest definition is brought down to the understanding of the youngest Junior before me, proud of the first pinfeather pricks on those lips that let us hope are as virginal as those of the erstwhile prophet Dowie's unkissed son. It was at an aviation meet that a youngster athirst for knowledge addressed to the blue-coated guardian: "Say, is it the altitude prize they're trying for now?" "Altitude, hell! It's the height prize." But to return to our slide: The vertical lines are a distance apart equal to the distance between the centers of the two lenses. Thus they represent vertical planes in parallel lines of sight placed edgewise and normal to the base line.

E

00000000

B

E,

6000 10000

FIG. 9.

AP2

Now note the tower points p1 and p2. They are at different distances from the reference verticals. This difference is proportional to their distance from the observing station. The geometry is made clear by an inspection of the horizontal plane diagram. I and II are the two lenses or observing stations, N M N is the distant plane in which the tower lies, ff are the parallel lines of sight and P is the tower point; t1 and to are the two photographic plates on which appear reduced images of the field of view, in this case the building. A line of sight from I to the tower in the distant field NN will intersect the