This invention relates to dual slide projectors for projecting images of picture slides onto a viewing screen, wherein the two projector units receive slides in alternating succession from a single slide magazine, and more particularly relates to feeding or indexing mechanism for moving the magazine in the proper sequence of steps so that the picture slides may be taken out of the single magazine in succession, in the same order in which they have been placed in the magazine, for delivery alternately first to one and then to the other of the dual projector units, and then may be placed back into the magazine in their original order so that they do not have to be rearranged before being again projected at another viewing event. 
Dual projectors receiving slides from a single magazine are known in the art.  One example is Carrillo U.S. Pat.  No.  3,093,030, issued June 11, 1963.  In this patent, however, the slides are not returned to the magazine after being projected, so that there is no provision for moving a magazine with the alternating two steps forward and one step backward (known as a "pilgrim step" movement) which would be necessary if the picture slides were to be returned to the magazine in proper order or sequence. 
Another example of a dual projector fed from a single magazine, is my own Sobotta U.S. Pat.  No.  3,847,472, dated Nov. 12, 1974.  In this patent, the pilgrim step movement of the magazine is accomplished, but it requires specially designed levers, guides, springs, and cam disks, so that it is somewhat complicated. 
Other examples of the prior art which may be considered in this connection are Floden U.S. Pat.  No.  3,462,215, dated Aug. 19, 1969, and the closely related Jackson U.S. Pat.  No.  3,501,232, dated Mar. 17, 1970; also the British patent of Grenier, No.  1,158,150, published July 16, 1969. 
An object of the present invention is the provision of an improved and more satisfactory mechanism for accomplishing the desired forward and backward "pilgrim step" movements of the magazine in a more efficient, simple, sturdy, and economical manner, as compared with the prior art. 
Another object of the invention is the provision of magazine feeding mechanism which is comparatively simple and inexpensive to construct, sturdy and reliable in use, and not likely to get out of order. 
A further object is the provision of such magazine feeding mechanism in a form which will perform the necessary special steps required for the commencement of a projection sequence when a magazine is first inserted into the projector, and the special steps required for returning the last slides to their proper positions at the end of the magazine when the projection sequence is completed, all without requiring any special attention or manipulation on the part of the operator. 
A still further object is the provision of magazine feeding mechanism which will operate independently of the slide transfer mechanism which takes slides from the magazine and places them in the respective projection gates of the projector units and then takes the slides back from the projection gates to the magazine, thereby providing magazine feeding mechanism of universal applicability, adaptable to any dual projector regardless of the form of the slide carrier or slide transfer means employed in the projector, and regardless of whether the magazine is arranged at the center between the two dual projector units or whether the magazine is at the outside of one unit, as in my prior patent above mentioned, and regardless of the direction in which slides are removed from and returned to the magazine, and regardless of whether the projector does or does not provide for axial movement of the slide holders or projection gates.