The University of Arizona and Smithsonian Astrophysical Observatory are jointly undertaking the development of the concept of a multiple-mirror telescope for astronomical uses. The system consists of six 1.8-m-aperture cassegrainian telescopes combined to produce a common focal surface in the center of the telescope. The early form of the telescope will provide for automatic alignment of the six independent systems. The telescope will be constructed to facilitate later extension of the alignment subsystem to include aperture synthesis (phasing) by methods proposed by Meinel and Shannon. The light-gathering power of the combination is equal to a standard telescope of 180-in. aperture, but the construction will cost very much less. The mounting will be of the alt-azimuth type. The telescope will be located at an elevation of 8,600 ft at the SAO's Mt. Hopkins Observing Station near Tucson.

The most common method of surface evaluation in optical production uses optical test plates. The main objections to test plates concern the possibility of damage to the surface through contact and the need for a different test plate for every different surface. A surface measuring interferometer is described which is capable of measuring the radius of curvature and the surface irregularity independently. The process of evaluating surface irregularity is simplified since all power error can be nulled out. Other useful applications of the interferometer are also described.

This paper describes a new method of holographically recording photogrammetric stereo-models. A twin projector system is used to form a stereomodel on a rear-projection screen. The two individual projections on the screen are recorded in a hologram independently by using two different reference beams. The holographic record of the stereomodel is viewed either through selective polarization of the reconstructing beams or through selective illumination of the hologram. A review of factors essential to the production of an accurate high resolution stereomodel indicates that "speckle" limits the resolution. For performing stereo presentation of photogrammetric data, holographic stereomodels have definite advantages over other types of synthesized 3-D holograms.

The rapid and intensive development of the field of electro-optics over the last decade has resulted in the production of a wide range of sensitive, photoelectronic imaging devices for applications in astronomical research. It is five years since Livingston) reviewed the applications of image intensifiers to astronomy but since that time existing devices have been further developed and new devices have been introduced. A wide range of devices is currently in use-this review will describe those devices which have found a wide measure of acceptance amongst observational astronomers and will mention some recently developed devices which show considerable potential.

One of the good things that could come out of the hard times of the past few years is the coalescence of several of the smaller technical societies, to form larger groups that can more effectively serve the interests of related fields. Such associations can benefit a field in several ways.

This volume is a popular account of the subject that appears to have been written in late 1968 or early 1969. Hence while a number of current topics of interest are discussed they are not done so in the kind of detail that the reader might expect.

Optical sensors for detecting obstacles on the guideway of a high speed transportation system were investigated experimentally and analytically. Both approaches are described in this paper. The performance of the optical sensor is dependent upon the extent of ray bending caused by solar heating of the air immediately above the guideway. The effect of ray bending is presented in terms of a relationship between obstacle size and length of the optical path.

The relation is shown between the two-dimensional chromaticity diagram, and the three-dimensional region of realizable colors in tristimulus space. Among the figures included is an artistic rendering of the boundary of this region in CIE coordinates. The CIE chromaticity diagram, much used in color photographic technology, is a planar system derived from three-dimensional coordinates. As part of a recent talk, the author had occasion to explain the way in which the diagram is formed. For this purpose, a series of illustrations was produced. Since it is more explicit and complete than what we have encountered in the literature,1 we present it here with some explanatory material. To the best of our knowledge, the inclusion of a view of the three-dimensional spectrum locus is unique. The chromaticity diagram is shown in Figure 1. as it is ordinarily used. Figure 2 is a perspective view in a coordinate plane of the overall tristimulus space. For the figures which follow, it is more convenient to view toward the origin from a point in the all-positive octant. The spectrum locus is shown from this view, in Figure 3. Chromaticity coordinates X, Y and Z satisfy the relation: X+Y+Z=1. This equation holds (only) for points in the "unit" plane, which intersects the coordinate axes as shown in Figure 4. The chromaticity diagram can be regarded as the projection vertically downward, from a corresponding region in that unit plane, as shown in Figure 5.

A Hasselblad camera has been used during all NASA lunar landings from Apollo 11 through Apollo 16. A few basic changes make it different from Hasselblad equipment used in previous space flights