that the object is partially submerged so that the water interface produced an irregular boundary.
• Her comment that one would expect more light diffusion or halation around the bright disk than is found here is interesting and raises a number of technical questions that requires far more space than is available to discuss. Suffice it to say that there are several other objects in the field of view that are brighter than the disk which possess extremely sharp edges (viz., roof tops of various buildings). In none of these regions is there significant light spillover from the roof area onto darker, adjacent areas of the film.
       The absence of a shadow from the disk remains a puzzle to us. As stated in our article, an obvious explanation is that the object is at the surface of the earth where no shadow would be expected. Another possibility is that the object is opaque, small, and much nearer the airplane so that its shadow's reduced size and darkness would be difficult or impossible to locate on the ground.

• Her reference to light areas on the negative, that is, "the 'portholes' on the positive image" is unclear. We did not use the term "porthole" or "portholes" and do not refer to any such areas. Perhaps she is referring to the single circular shaped region at the approximate center of the disk which is a good deal lighter than the average luminance of the disk (on the negative). That particular region is approximately the same density as is the surface of the lake surrounding the disk.

We have two major comments concerning this possibility. The first has to do with the kind of an 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