through the two positions of the same object, we get the direction of the motion. Now, look to the right and we see a protuberance with a triplicate form. Here, then, the telescope must have received two blows; and by drawing a line along the top of the three figures, we get the direction of the motion, or disturbance; and on looking at the different directions of the two motions, we see that the telescope moved two ways at once, and also, that one part of the plate was disturbed once, whilst another part of the same plate was disturbed twice--which is absurd; and lastly, Mr. Vail who had not seen the photograms when he wrote his report, gives a description of certain lines and cracks that are to be seen in the negatives when they are examined by a lens. How is it possible to get over this? Here, an American gentleman sees with a telescope exactly what is photographed. But this is negative testimony; I will now prove, conclusively, giving geometrical evidence, that Mr. De la Rue has made an egregious misstatement. The reader will have it in his power to corroborate this testimony. Place a piece of paper behind the photograms III. and IV. (taken in the principal focus), and with a needle make holes in four or five different places, taking care not to mark the bottom of a protuberance, which is a notch, but where you can see distinctly the limb of the moon; then remove the paper and find the centre of three holes, and draw a circle through them; and if it passes over the other holes, you have positive proof that the centre did not move during the exposure. Now, look at the lithograph, and you will see a circle drawn through five marks made upon the limb of the moon of No. III., and through four marks made upon the limb of the moon of No. IV.--_Q. E. D._ [Photograph: IV.] Having proved that the very remarkable photograms taken at Jefferson are correct representations of the phenomena seen at that place, I will proceed to describe the details of the four negatives that are to be seen when examined with a lens.