Memoir on a Trans-Neptunian Planet.


LOWELL, Percival. ‘Memoir on a trans-Neptunian planet.’ Offprint from Memoirs of the Lowell Observatory, Vol. 1, No. 1. Lynn, Mass.: T. P. Nichols & Son, 1915.

First edition, the most desirable possible presentation/association copy, of Lowell’s prediction of the existence of a planet beyond the orbit of Neptune, which initiated the search that culminated in 1930 with the discovery of Pluto at Lowell Observatory by Clyde W. Tombaugh (1906-97): this copy is signed both by Lowell and Tombaugh. “Clyde Tombaugh’s February 18, 1930, discovery of Pluto concluded a three-stage search at Lowell Observatory in Flagstaff, Arizona, spanning 25 years. What started with Percival Lowell’s musings about a theoretical ninth planet led to mathematical and photographic studies that survived Lowell’s death and set the stage for Tombaugh’s eureka moment … The first phase of Percival Lowell’s hunt for Planet X ran from 1905 to 1909 … Lowell and his small team of ‘computers’ – led by head computer Elizabeth Williams – carried out a series of calculations based on the observed perturbations of Uranus, pinpointing likely locations for the new planet … [In 1910] Lowell redoubled his mathematical efforts by incorporating the latest technology …With new calculations and improved equipment, Lowell estimated locations of Planet X and published his findings in the 1915 Lowell Observatory publication, Memoir on a Trans-Neptunian Planet. Unfortunately, Lowell died the following year, before he had a chance to complete a photographic search in the targeted area of the sky. Eleven years after Lowell’s death, the final phase of the Observatory’s search for Planet X commenced … Abbott Lawrence Lowell, Percival's younger brother and president of Harvard University, gave $10,000 for the construction of a new telescope, a 13-inch photographic instrument usually referred to as an astrograph. To operate the telescope, director V. M. Slipher hired a young man from Kansas of ‘the self-made type,’ Clyde Tombaugh. Tombaugh arrived in Flagstaff in 1929 and soon took over the systematic search for Planet X, examining the area of sky Lowell had indicated in Memoir on a Trans-Neptunian Planet. The 13-inch telescope was ideal for the search, and Tombaugh had the patience and attention to detail necessary for the work. On February 18, 1930, he discovered what would soon be named Pluto, completing the search begun by Percival Lowell 25 years earlier” (Schindler). “More than any other astronomer of his generation, Percival Lowell (1855-1916) had a profound influence on the general public. His thesis that the planet Mars was the abode of intelligent life continued to excite the public mind decades after his death … Lowell’s name is also forever linked with Pluto; although he did not live to see that distant planet, there is no doubt that his inspiration advanced the date of its detection by many years” (DSB).

Provenance: Percival Lowell (signed book label on half-title); Clyde W. Tombaugh (signature on half-title).

A member of the distinguished Lowell family of Massachusetts, Percival Lowell devoted his early years to literature and travel. Beginning in the winter of 1893–94, inspired by Giovanni Schiaparelli’s discovery of ‘canals’ on Mars, Lowell decided to dedicate himself to the study of astronomy, founding the observatory at Flagstaff, AZ, which bears his name. In 1904, Lowell received the Prix Jules Janssen, the highest award of the Société Astronomique de France, the French astronomical society. For the last 23 years of his life astronomy, Lowell Observatory, and his and others’ work at his observatory, were the focal points of his life.

“As early as 1902, Lowell was lecturing and writing about his conviction that a planet existed beyond the orbit of Neptune. He had studied the orbits of a number of comets and had noticed gaps and groupings which he felt were significant. In 1905, the first of his two extended searches for ‘Planet X’ began. This phase lasted until 1909, and was essentially carried out by Lowell, a trio of graduate assistants and William T. Carrigan, a ‘computer’ from the US Naval Observatory’s Nautical Almanac Office in Washington DC. Lowell employed Carrigan to perform a number of calculations on the orbits of Uranus and Neptune. Lowell was interested in ‘residuals,’ differences between the calculated positions of the planets and the positions which were actually observed.

“Lowell’s second search spanned the years 1910-1915. This search was based upon calculations using the formulae of celestial mechanics. In essence, it was similar to the predictions of Adams and Le Verrier [for the orbit of Neptune], but using residuals which were much smaller. The calculations, thus, were much more difficult and involved. This search culminated in the publication entitled ‘Memoir on a Trans-Neptunian Planet,’ in Memoirs of the Lowell Observatory, vol. 1, 1915” (Bakich, p. 299).

“Lowell himself recognized the difficulty of the problem he was trying to solve. In his 1915 paper ‘Memoir on a Trans-Neptunian Planet,’ he pointed out: ‘We cannot use Neptune as a finger-post to a trans-Neptunian as Uranus was used for Neptune because we do not possess observations of Neptune far enough back.’ (In fact, Galileo had unknowingly observed Neptune, on at least two and possibly as many as four occasions, from late December 1612 into early 1613. These observations might have helped Lowell enormously; however, Galileo’s observations of Neptune were not recognized until 1979, in work by Stillman Drake and Charles Kowal.) Lowell further noted that in 1845, when Adams and Le Verrier used the residuals in the orbit of Uranus to predict the existence of Neptune, the difference between the predicted and observed positions of Uranus sometimes amounted to 133 seconds of arc. In contrast, after accounting for the gravitational influence of Neptune on Uranus, the remaining residuals in the orbit of Uranus never exceeded 4.5 seconds of arc.

“Lowell used the tried-and-true mathematical methods of Adams and Le Verrier – examining the apparent residuals in the orbit of Uranus – and an assumption that the semi-major axis of [the orbit of] Planet X would be close to 47.5 AU, to work out his initial prediction for the location of Planet X. He apparently started his calculations with an assumption akin to the Titius-Bode rule: the relative distances of all planets were determined by a not-as-yet-understood physical principle that forced the ratios of orbital periods of neighboring planets to be close to ratios of small integers … Lowell asserted that because the ratio of the orbital period of Neptune (164.8 years) to that of Uranus (84.0 years) is very nearly two, the ratio of the orbital period of Planet X to that of Neptune also should be nearly two. According to Kepler’s third law, if Planet X were in an orbit with a semi-major axis of 47.5 AU, it would have an orbital period of 328 years, which is almost twice the orbital period of Neptune …

“From 1906 through 1916, Lowell directed a photographic search of the sky for Planet X. Amazingly, two of the photographic plates obtained at Lowell Observatory in 1915 contain images of Pluto, but because Lowell was looking for a much brighter object, his sought-after Planet X slipped through his fingers.

“When Lowell died in 1916, his hypothesized Planet X remained hidden in the darkness of the outer solar system. It would take the better part of a decade after his death for the finances of Lowell Observatory to get sorted out, but by 1927 the observatory, newly under the leadership of Percival Lowell’s nephew Roger Lowell Putnam, decided to launch a new search for Lowell’s planet and to hire an amateur astronomer to assist in the program” (Weintraub, pp. 133-136).

“Plans were formulated and money was secured for a new photographic telescope to better continue the hunt. The 33cm A. Lawrence Lowell Astrographic Telescope took its first exposure in the hunt for the trans-Neptunian planet on 6 April 1929. It was an hour-long exposure centred on the star δ Cancri. The man at the telescope was Clyde Tombaugh.

“Tombaugh had been corresponding with Vesto Melvin Slipher, Director of the Lowell Observatory, during 1928. Early in 1929, Slipher offered Tombaugh a position to work with the 33cm Astrograph. Tombaugh traveled from Burdette, KS, to Flagstaff, AZ, arriving at Lowell Observatory on 15 January 1929, with absolutely no idea he would be conducting a search for a new planet.

“Tombaugh exposed more than 150 plates before his epic exposures on 23 January 1930 and 29 January 1930. Even then, the discovery was not immediate. To examine the plates, Tombaugh used the observatory’s blink comparator, where first one plate is illuminated and then the other. A small portion of the plates is studied with a microscope incorporated into the apparatus. The necessity of blinking other plates meant Tombaugh did not examine the exciting pair until several weeks after they were first exposed. Then, according to Tombaugh’s notes, on 18 February 1930 at 4pm, Planet X was discovered on the comparator.

“V. M. Slipher was a cautious man. He wanted confirmation that the object identified by Tombaugh was indeed Percival Lowell’s long-anticipated Planet X … But Slipher also wanted the opportunity for Lowell Observatory to observe the newest addition to the solar system for as long as possible without competition.

“Finally, on 13 March 1930, on what would have been the seventy-fifth birthday of Percival Lowell, the announcement was made. It is interesting to note that this was also the date of the first planetary discovery since antiquity, by Sir William Herschel, 149 years earlier. The Lowell Observatory’s reputation was secure, and Clyde Tombaugh – who less than two years before his discovery was a farmboy on the plains of Kansas – was assured a place in history” (ibid., pp. 299-300).

The announcement in the Lowell Observatory Circular read: “Systematic search begun years ago supplementing Lowell’s investigations for Trans-Neptunian planet has revealed object which since seven weeks has in rate of motion and path consistently conformed to Trans-Neptunian body at approximate distance he assigned. Fifteenth magnitude. Position March twelve days three hours GMT was seven seconds of time West from Delta Geminorum, agreeing with Lowell’s predicted longitude.”

“Mrs. Constance Lowell naturally felt she had some say in the matter of naming the planet her husband had sought after for so long. She first suggested Zeus, then decided that ‘the gods of the past are worn out.’ She tried Percival, after her husband, then Constance, after herself, but these were politely turned down, or ignored altogether. Many others suggested Percival or Lowell, but the astronomers at the observatory were in favor of a classical name.

“The name Pluto was first suggested by Venetia Burney, an 11-year-old schoolgirl in Oxford, England. She had been studying Greek and Roman mythology in school, and felt that the planet, being far from the Sun in its own dark world, should be named after the Greek god of the underworld. The observatory officially proposed the name Pluto on May 1, 1930, with the symbol being PL, the first two letters of Pluto and coincidentally the initials of Percival Lowell” (

In 2006, the International Astronomical Union voted to strip Pluto of its planetary status, making it the first member of a new class of objects called ‘dwarf planets.’ This decision has proved controversial, among both professional and amateur astronomers.

E. Bakich, The Cambridge Planetary Handbook, 2000; P. M. Sadler, ‘William Pickering's Search for a Planet Beyond Neptune,’ Journal for the History of Astronomy, Vol. 21 (1990), pp. 59-64; K. Schindler, ‘Percival Lowell’s three early searches for Planet X,’, May 14, 2015; D. A. Weintraub, Is Pluto a Planet? A Historical Journey through the Solar System, 2014.

Offprint from Memoirs of the Lowell Observatory, Vol. 1, No. 1, 1915. 4to, pp. 105 with nine plates (two double-page). Original printed wrappers (offsetting on wrappers probably caused by storage in corrugated cardboard, otherwise a fine copy).

Item #4725

Price: $3,500.00

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