canal at Summit, Ill., and running up the canal 5 miles to the northeast, to the first bridge.
At the beginning of the line of experiments, a target 22 inches in diameter was fixed upon a staff
Under the bridge from which the above observations were made, two large targets (one 21x27, the other 26x38 inches) were fastened side by side so that the lower edge of each was 7 inches above the water. The paper of which they were made was white, and they were placed in the sunshine directly beneath the bridge. When the boat was rowed three miles on the return trip, observation was made with the telescope 12 inches above the water; the entire surface of the targets was plainly visible above the water. Upon returning to the first target, 5 measured miles from the bridge, the boat was anchored; the sun was shining brightly upon the paper targets under the bridge; the targets were visible at this distance to the unaided eye of each observer in the boat, the eye being about 30 inches above the water. The canal was quiet and still, with scarcely a ripple on its surface; the conditions were the best and most favorable for the final tests and observations of these experiments. A particular observation was made without the telescope. As the eye came within 15 inches of the surface, the targets became invisible; upon raising the eye again they came into view. Repeatedly the eye was lowered, but each time the targets could not be seen. The result of the comparison of the conditions of observation with the accredited convexity is the same as in the case of the first target from the view under the bridge, with the instrument 6 inches above the water. The tops of the targets, if the water were convex, should have been 9 feet 10 inches below a direct line extending from the eye over the apex of the bulge to the terminus of the five miles. The accompanying diagram illustrates what would be the conditions and relations of the eye, the line of sight to the occulted objects, upon the basis of the calculated convexity. T represents the telescope, 6 inches from the surface; A, the apex, ¾ of a mile distant; S, the