That is what L. Jackson Bulliet, of 7609 Fourth Avenue, Brooklyn, N. Y. had in mind when he submitted to us a memorandum containing an idea which he wishes to present for all and sundry to wrestle with.

"The following discussion," Mr. Bulliet writes, "is concerned with a device to eliminate the necessity for an observer giving constant attention to the guiding of a photographic telescope. It is believed that such a contrivance would not only save the photographer from an exceedingly tedious job on long exposures, but would also result in better pictures. The reason for expecting better pictures is that this device should respond at once to a drift so slight that it would not be noticed by a human observer. Thus, corrections would be more frequent than with the method now used, resulting, in effect, in a steadier position of the image on the plate.

''Considering Figure 1, the reader is looking into the top of a round light-tight metal box B. This box is divided, for its entire depth, into quadrants by the exceedingly thin opaque partitions P and P'. It may be well to make the actual partitions of glass, with one side of each coated with a thin opaque film. The films may then be regarded as the partitions here referred to. In each quadrant is mounted a photo-electric cell R, R', D and D'.

"Suppose now that this box is affixed to the eye end of the guide telescope of a photographic telescope in such a manner that the top of this box coincides with the focal plane of the telescope. The connection to the telescope must be light-tight, so that no light may reach the photocells except through the object glass of the guide telescope. The top edges of the opaque partitions now correspond to the cross-hairs of the guide telescope. The box is oriented as indicated by compass points on the sketch. That is, the cross-hairs (partitions) lie NE, SW, and NW, SE, with respect to the telescopic field. At the intersection of the cross-hairs (partitions) is an opaque disk M, slightly larger than the image of the object to be guided upon. This disk would actually be a spot on a removable glass cover or slide over the box, so that different sized disks could be used for different sizes of images. If the field of view included objects other than the one to be guided upon, an opaque diaphragm (not shown) with a center opening somewhat larger than the disk M, would have to be provided to keep the light from the other objects from reaching the photocells.

"So long as the object is centered on the cross-hairs (partitions), no light can reach any photocell because of the disk M. But any drift will cause the image to creep off the edge in some direction so that light will fall into one or two (if over one of the thin partitions) of the compartments where it can affect the cells in them. This effect could be greatly enhanced by fitting a triangular mirror into the corner of each quadrant, to reflect the light directly into the cell. The apex of the mirror would be at the top and the base at the bottom of the box, so that the four mirrors would form a pyramid. Perhaps a better arrangement would be to leave out the partitions entirely, and place in the center of the box a square based pyramid of optical glass with its faces silvered and with its apex just under the disk M. This pyramid would be oriented as indicated by dotted lines in the figure. The rest of this discussion will continue to refer to the partitions and the rest of the arrangement as first described, but the argument would not differ essentially in the pyramid scheme.

"Referring now to the wiring diagram. Figure 2, it is seen that each photocell feeds through an amplifier into a relay. The relays associated with the cells R and R' control a reversible electric motor C, which drives the regular slow motion screw on the right ascension axis, or a special screw provided for the purpose. Likewise, the cells D and D' control the similar motor C', on the declination screw.

"Should the image in question drift toward the northward with respect to the cross hairs (partitions), the cell D would function to start the motor C' in proper; direction to compensate for the drift. Similarly, a drift to south would start the same motor in the opposite direction; and the same reasoning applies to drifts in right ascension. The more general case, of course, is that in which the drift is in some direction other than the cardinal compass points. The light would probably fall in only one quadrant in this case but, the correction being in a cardinal direction, the light would fall into another quadrant before it got back to the center. Thus the correction would be brought about by motions in right ascension and declination successively or simultaneously (the latter when the image falls on a cross-hair).

"It will be noted that the circuit to start a motor includes contacts of both relays associated with that motor. Thus the operation of one relay will not start the motor unless the other relay of the pair is unoperated. The idea here is that in time of poor seeing the image might become fuzzy and larger than the disk M. In that case. both cells associated with each motor would be energized. Neither motor, however, would start, due to the relay circuit. In other words, any anomalous condition tending to bring about directly opposing corrections would cancel out.

"Another possibility in times of poor seeing would be rapid shifting of the image in random directions. This would tend to bring about incessant efforts to correct for erratic motions for which corrections are inherently impossible due to inertia of the telescope mechanism. By using relays of the type which have a slight lag in their operation, these rapid shimmerings would not operate the relays and so not start the motors. Only the drift would be corrected for."

WE passed this communication to Mr. Alan R. Kirkham of Tacoma, who commented as follows:

"The photocell tracking device interests me. As a radio nut, the thing looks OK, except for the terrible cost, and awful difficulties of making large amplifiers work. The worst bug I see is this: the gadget that splits the rays is much larger than a star image. The prism, for example, cannot be made with edges good enough. The size of a star in the focal plane of a very good 12-inch telescope runs from 1/2000 to 1/10,000 inch in diameter, depending on the focal length."

The above comment was relayed back to Mr. Bulliet, who replied:

"As I wrote the paper, the apex of the pyramidal prism was to be placed exactly in the focal plane of the guide telescope objective. Now, as Mr. Kirkham points out, the said apex would necessarily be somewhat larger than the image of the star on which we are to guide. Hence the star may drift more than its own diameter before light will have a chance to strike one of the sides of the prism and be reflected into a photocell, That would, of course, be an intolerable drift. But suppose we introduce a convex lens or lens-system between the focal plane of the objective and the prism and put the prism back far enough so that it will be in the plane of the new image (equivalent of using eye-piece and eye and putting the prism at the retina of the eye). Now the drift will be greatly magnified (assuming proper placing of the new lens) but the dimensions of the prism have not changed. Also, if we are dealing with a star, the actual image of the star will not be increased. It seems to me that the new arrangement should work all right because the secondary image of the star will move several times the width of the prism point before the primary (photographic) image has moved a perceptible distance."

Well, there you are, folks, just as these two left it-probably in a pretty raw stage at present but ready to be improved and made to work. Somebody ought to derive some fun perfecting this thing-not to speak of the fame.

SEVERAL workers have inquired about making rifle telescope sights, and we have advised them that we had no data but to go ahead and see what they could finally work out and then make their findings available to the rest of the amateur telescope-making fraternity who might have similar interests. An effort of this kind is being made by Harry A. Peck of 205 Kenmore Avenue, Youngstown, Ohio, who is also making a rifle-barrel, receiver, bolt and all-while he is at it. He says the telescope sight will cost him around 35 dollars, not to mention his time. Those who may be interested in this endeavor might well pool their knowledge with Mr. Peck.

LAST month we omitted a credit line and we hope we can make amends by saying here more than the credit line could have said, had we not plain forgotten it. On page 28 of last month's number there: was a short article about Professor R. W. Wood and his original inventions, including infra-red photography, and one illustration used with that article showed the Empire State Building in New York, taken from a distance of 18 miles ( Paterson N. J.) with a six-inch telescope, by infrared photography. What was omitted, Professor Wood tells us, was the photographer's name, Mr. Garret Hobart, Jr. We don't knowingly suppress such things but we do sometimes unknowingly forget them. Taking that picture was quite a feat.

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