Free Astronomy Magazine January-February 2020

10 JANUARY-FEBRUARY 2020 HISTORY a 5-inch refractor, but on the 440 plates exposed for about 3 hours each there was no suspicious ob- ject. The only result of that first survey was the alleged discovery of two comets, which turned out to be non-existent, adding dis- credit to the figure of Lowell and his observatory. After the setback, the search for Planet X resumed with greater vigor when the observatory was equipped with a new 42-inch re- flecting telescope that greatly accelerated image acquisition (seven minutes instead of three hours), but that, on the other hand, compared to 5-inch refrac- tor, covered areas of the sky ten times smaller. Considering that any possible positions of Planet X provided by Lowell were approxi- mate (to say the least), it was necessary to expose many hundreds of plates in large re- gions of the zodiacal constellations to have any hopes of a discovery. Comparing the positions of the stars contained in these plates to find suspicious movements would have been a very hard task without the invention (in 1904) of a new lab- oratory instrument − the blink com- parator, a kind of microscope that allowed one to observe in rapid and continuous succession two photo- graphic plates, highlighting, in the form of a flickering, every stellar- looking object that had moved in the interval between the exposures. Lowell bought the blink from Zeiss in 1911 and the observatory team used it with plates taken by the 42-inch scope up until the following year without discovering anything partic- ularly interesting. Wanting to try new solutions, Lowell borrowed a 9-inch astrograph from the Sproul Observatory (Swarth- more, Pennsylvania) in 1912, hoping that the large field of that instru- ment would serve as a turning point in the hunt for the elusive planet. This third research campaign ended on November 12, 1916 with the death of Lowell, who therefore did not see his dream realized. In actual- C lyde Tombaugh (second from left) at harvest time on the Tombaugh family farm in Kansas. Left to right: Charles, Clyde, Adella, Roy, Anita, Robert, Esther, Patsy. Beside, the young amateur astronomer next to the 9-inch tele- scope he built in 1928 at the age of 22. [Lowell Ob- servatory Archives]