DR. FERCIVAL LOWELL, of the Lowell Observatory at Flagstaff, Ariz., has been finally successful in obtaining photographs of Mars, which establish beyond a doubt the reality of the canals of Mars. Heretofore, the value of the photos obtained by him in 1907 was questioned, on account of their minuteness, being compared in size to the head of an ordinary pin. Doubts were expressed as to the amount of detail which could be seen on so small a scale, and magnification, it was said, only increased the difficulty by enlarging the silver particles upon the plate, wherever its sensitive surface had been exposed to the light. With regard to photographs of Mars obtained October 11th, 1911, with the Lowell refractor, 24 inches aperture, the images made at one minute intervals of exposure, each of three seconds, Dr. Lowell writes as follows, in a letter dated November 9th, 1911: “The following, therefore, will interest you and the public generally—the magnification used for the photographs is now 178 diameters. This on a disk of twenty-four seconds of arc which Mars presented at the last opposition gives for the photographic images a diameter 2.3 times that of the Moon to the naked eye, and a superficies of over five times that presented by our satellite to naked eye vision—rather a surprising revelation this as to the size of our photographs. “Believe me, yours very truly, "(Signed) PEECIVAL LOWELL." The diameter of Mars at the last opposition was twenty-four seconds of arc less than now. Superficies, in the above letter, means surface of original photographic images which then covered an area over five times that presented by the full Moon to the naked eye, the telescope magnifying one hundred and seventy-eight diameters. While the canals are plainly visible on the photographic plate, they will not bear printing processes. On examining the enlarged image through a screen by a stereopticon an immense amount of elaborate detail appeared, several of the canals being plainly in evidence. As these photographs were taken a month or so before Mars had reached its nearest to our planet, we may look forward with interest to those which will be obtained on the date of nearest approach.
This article was originally published with the title "The Latest Photograph of the Planet Mars" in Scientific American 105, 23, 495 (December 1911)