We have two major comments concerning this possibility. The first has to do with the kind of optical image that could be produced purely by a "pressure mark" caused by a "foreign particle trapped between two layers of the film on the supply spool," in the words of Dr. Bruner. If the particle merely produced a dimple in the unexposed film and then came off the film prior to exposure then one would not expect such a highly geometric pattern of light and dark regions produced by the incoming rays from ground-reflected sunlight. It is also unclear how such a film deformation could occur without leaving an oval-shaped region of deformation in both the size and spatial distribution of the film grains in that region. A careful examination of the second generation negative shows no such grain deformation. Second, if the particle somehow remained attached to the unexposed film as it rapidly spooled forward within the camera, it would have had to be located on the lens side of the film so its shadow could have differentially exposed the film. Subsequently, as the roll of continuous film spooled on top of itself on the take-up reel, it would have produced another (smaller) dimple there on adjacent film. It is likely that this secondary dimple would have produced a slight physical (and optical?) distortion either on preceding and/or following frames in an equivalent position on the film. The linear distance between these successive dimples would be approximately the same and a function of the circumference of the film reel at that point. Linear distances between successive dimples would range from 9.42" to 14. 1" corresponding to take-up reels with film having diameters of from 3" to 4.5", respectively. A careful examination of frames 299 and 301 show no areas of distortion at the same distance from the edge of the film and between 9.42" and 14. 1" on either side of the disk's image position.
In order for thickness variations of an adhered particle to account for the present disk image detail the particle must remain stuck to the film during its initial exposure and must possess a highly geometric pattern of light transmission. While this is possible, it is considered highly unlikely.
If the particle somehow shifted position it would have to have occurred during the optical exposure period of 1/500th second. Several issues arise: (a) Why isn't there a set of double edges on the opposite side of the disk as well? (b) Also, the disk's off-optical axis location on the film would have produced a continuous differential density within the two boundaries on the easterly side of the image rather than only a set of two darker lines with lighter region between them. (c) Finally, a differential blur of these two lines should occur at intermediate points around its circumference. There does not appear to be any such blur.
Dr. Bruner's suggestion to examine the original negative using oblique illumination is an excellent one. However, her suggestion that the disk is due to an optical effect produced by an adhered foreign particle is not supported by a careful analysis of the negative that is in our possession. We are continuing to try to obtain the original negative for further study.
