In the last four sets of observations the speed was lowered from 256 turns to 192, 128, 96, and 64 turns per second. The results with these speeds were the same as with the greater speed within the limits of errors of experiment. Bias. Finally, to test the question if there were any bias in taking these observations, eight sets of observations were taken, in which the readings were made by another, the results being written down without divulging them. Five of these sets are given in the "specimen," pages 133-134. It remains to notice the remarkable coincidence of the result of these experiments with that obtained by Cornu by the method of the "toothed wheel." Cornu's result was 300400 kilometers, or as interpreted by Helmert 299990 kilometers. That of these experiments is 299940 kilometers. Postscript. The comparison of the micrometer with two scales made by Mr. Rogers, of the Harvard Observatory, has been completed. The scales were both on the same piece of silver, marked "Scales No. 25, on silver. Half inch at 58° F., too short .000009 inch. Centimeter at 67° F., too short .00008 cm." It was found that the ratio .3937079 could be obtained almost exactly, if, instead of the centimeter being too short, it were too _long_ by .00008 cm. at 67°. On this supposition the following tables were obtained. They represent the value of one turn of the micrometer in millimeters. Table 1 is the result from centimeter scale. Table 2 is the result from half-inch scale. Table 3 is the result from page 31. It is seen from the correspondence in these results, that the previous work is correct. (1) (2) (3) From 0 to 13 .99563 .99562 .99570 25 .99562 .99564 .99571 38 .99560 .99572 .99576 51 .99567 .99578 .99580 64 .99577 .99586 .99585 76 .99582 .99590 .99592 89 .99590 .99598 .99601 102 .99596 .99608 .99605 115 .99606 .99614 .99615 128 .99618 .99622 .99623 140 .99629 .99633 .99630 End of the Project Gutenberg EBook of Experimental Determination of the Velocity of Light, by Albert A. Michelson