【正文】 vements of the carriages l and 2. The extent of movement of the carriages l and 2 is closely controlled by an interferometer 10 mounted thereon. The interferometer includes a source of monochromatic light, such as a cadmium vapor discharge tube 11 coupled with a narrow band filter 12. The near monochromatic light issuing from filter 12 is passed through a collimating lens 13 which directs a column of light into a dividing prism 14, prising tw0 306090 degree prisms 15 and 116 cemented together. Significantly, at least one of the prisms 15, 16 is aluminized at their union face 17 so that equal amounts of light will be reflected and transmitted by the plane of union, the reflected light being designated by the arrows R and the transmitted light by the narrows T. From the dividing prism 14 the reflected and transmitted light R and T pass into tetrahedral or corner prisms 18 and 19, respectively, which characteristically reflect light back along a path parallel to its path of entry, even though the prism is displaced in any direction transverse to such path of entry. After being reflected from their respective tetrahedral prisms l8, 19, the reflected and transmitted light R and T return to the dividing prism 14 where each is again divided by the plane of union 17. Here we are concerned with the transmitted ponents of the originally reflected light R and the reflected ponents of the originally transmitted light T both issuing from prism 14 along the lines R T toward a lens 20 which controls the diameter of the column of light impinging upon a shield or mask 21 having an annular aperture 22 there through which permits only a ring of light coincidental there with to pass and impinge upon a photoelectric cell 23 which converts pulses of light into electrical pulses. It will be noted that all ponents of the interferometer 10 are mounted on one carriage l except only one of the reflectors or tetrahedral prisms 18 which is mounted on carriage2 to move therewith. As is well known in interferometers, relative movement between the reflecting prisms 18 and 19 will vary progressively the phase relationship of the light reflected therefrom and reunited in its exit from dividing prism 14. That is, a prism movement of onehalf wave length will increase the distance traveled by the light over both the paths of incidence and reflection of one full wave length. Consequently, after a relative movement of onehalf wave length, the originally reflected and transmitted light waves R and T will exit toward shield 21 in phase again. By the same token, a relative movement of onefourth wave length will cause the reflected and transmitted light R and T to exit from prism 14 in interference, . onehalf wave length out of phase. Consequently, 濟(jì)南大學(xué)畢業(yè)設(shè)計(jì) 外文資料翻譯 5 continuous movement through the maximum light of phase coincidence and the darkness of interference produces a successively light and dark fringe pattern which from the collimated light l emitted from lens 13 is in the form of concentric rings moving outwardly from or inwardly toward the center, depending upon the direction of relative movement between reflecting prisms 18 and 19. As each ring of light in the fringe pattern produced assumes a diameter wherein it coincides with the annular aperture 22 of shield 21, a pulse of light impinges upon the photoelectric cell 23 to be converted into a pulse of electricity fed by conductors 23a to an electronic counter arid control circuit 24 for counting such pulses. Thus, relative movement between the reflecting prisms 18 and 19, and hence carriages l and 2, can be indicated by electrical pulses in increments of onefourth wave length of the monochromatic light emitted from source 11. Of particular significance is the capability of my apparatus to extend this indication or measurement of minute increments over a total travel of the carriages l and 2 limited only by the length of the ways 5 and 6. The electronic counter and control circuit 24 functions to control the speed of the carriages l and 2 and the operation of electrical switches in accordance with the receipt of given numbers of electrical pulses. Through such switches, a source of alternating current 25 may be varied and selectively connected through conductors 26 and 27 to motors 7 and 8, respectively, driving carriages l and 2. For example, when the carriages l and 2 are in the position shown, a signal produced the counter and control circuit 24, will close an appropriate switch to direct current from the source 25 to the motor 8 for driving the leading carriage 2. During this movement intermittent fringes impinge upon photoelectric cell 23 to produce electrical pulses to be counted by control circuit 24. When a predetermined number of pulses have been counted, the circuit of motor 8 is opened to stop further movement of the carriage 2. The number of pulses measuring this movement is determined by the effective range of the interferometer 10. That is, the relative movement of this and, in fact, all interferometers must be within a range wherein the fringe pattern produced thereby is sufficiently sharp and brilliant to effect reliable functioning of the photoelectric cell 23. Therefore, assuming that the reflecting prisms 18 and 19 as illustrated in FIG. 2 are within the usable range, the carriage 2 may be moved until prism 18 has moved from the left of prism 1939。 of metal, glass plastic or the like. The grid blank 30 may be held stationary by any conventional fasteners, clamps or other holding means and disposed as shown with its longitudinal axis parallel to the ways 5 and 6 and its transverse axis perpendicular to the plane of the carriages 1 and 2. On the adjacent surface of the grid blank 30 is a coating 31 of a light sensitive emulsion requiring the maintenance of controlled conditions of area illu