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The Implications Of Percival Lowell’s Theory-laden Observations Of Mars

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A recurring debate in scientific research is the effect of theory-laden observations. Scientific observation is regarded as theory-laden when one’s beliefs, assumptions, or expectations are used to interpret observations. When investigators observe a distant world, everything that their senses convey is interpreted by the observer through cognitive processes that consider their prior training, cultural factors, and environment. In this way, the investigator tries to identify and organize the impression based on prior knowledge and preconceptions.

In his scientific structure Thomas Khun, philosopher of science, argues that theories and observation have an intimate relationship as the investigator is unable to possess a neutral perception. Observations are filtered through the beliefs that occur as a result of theory, therefore observations can only have meaning in relation to the theory influencing the investigation. (Khun, 1970) Theories help to understand what the senses are conveying while preconceptions point the observer to a conclusion.

The term theory-laden literally means loaded with theory, although it refers to the observations or perceptions made by the investigator rather than referring to actual theories, and it applies to both naked eye and equipment-based observations. Theory-laden observations begin during childhood when experiences and cultural influences are shaping a child’s understanding of their environment with the process continuing throughout the individual’s lifetime.

One of the best examples of this interdependent relationship of theory and observations is the study of the planet Mars.

Canals on Mars

During the summer of 1877 as Mars was reaching opposition with Earth, Giovanni Schiaparelli (1835-1910), Italian astronomer at the Brera Observatory in Milan, began mapping the planet using an 8 ¾ inches aperture telescope. He observed separate light and dark areas on the surface which he designated as continents and seas or terrae and maria. Schiaparelli also observed glimpses of vast and intricate streaks in the dark shading of the continents which he named canali. (Fig. 1) This directly translates to the word “channels” in Italian. The term had already been used in the 1850’s by Father Angelo Secchi, who had observed a vague streak in one of Schiaparelli’s continents and designated it a canale.

The Italian astronomer was wary of drawing conclusions as to what the lines were or what their purpose might be. He noted that the canali were often difficult to detect and appeared to have varying degrees of shading which could have been due to the visibility and the red colour of the planet’s continents. (Sheehan, 1997) The fact that he was colour blind and myopic, or severely near-sighted, may have been a contributing factor in his observations as well. However, Schiaparelli was adamant that the lines were not an optical illusion and that he believed them to be real features of the Martian landscape.

While observing Mars in 1879 during the spring opposition, Schiaparelli began to distinguish double lines appearing in the canali. He attributed this “gemination” as he called it, to the seasonal changes of Mars, as observations in 1877 had not produced any doubling. Further observations during the January and February 1882 opposition only produced further gemination which furthered his theory that it was seasonal.

As Schiaparelli’s maps of the lines criss-crossing Mars began circulating, the term canali was almost predictably translated into the word canals. Around the world, astronomical and public interest in Mars heightened as people began to debate whether the lines were indeed real or rather just an optical illusion. Later drawings in which Schiaparelli included the doubling of the canals only furthered the debates with many astronomers weighing in on the topic. The idea that there could be such numerous and complex canals on a distant world hinted at the work of intelligent lifeforms. While many astronomers were sceptical of this some, like the French astronomer Camille Flammarion, were more open-minded to the idea of an inhabited Mars. Flammarion pointed out that the canals could be a network of waterways while conjecturing that there may be seas and shorelines that would make it an agreeable place to live for any inhabitants. He noted, “Yet we hope that, because the world of Mars is older than ours, mankind there will be more advanced and wiser.” (Hoyt, 1976, p.7)

Schiaparelli likely did not believe that the Martian lines were canals. He went back and forth fluidly in describing them as canali and fume or river, while assigning the names of Earthly rivers to each streak. (Sheehan, 1997)

As the interest in Mars and its canals began to gain momentum in the late 1880’s creative novels and magazine articles began appearing which resulted in a surge of Mars interest with the public. Although Schiaparelli was the only person at that time to have observed the canals, the idea sparked fresh interest in Mars planetary observation within the astronomical community. New telescopes were being built at well-known observatories for studying the Martian landscape. The 30.3-inch refractor was built in Nice in 1886, the 36-inch refractor at the Lick Observatory in 1888 and in 1893 Percival Lowell completed the Lowell Observatory in Flagstaff, Arizona.

Mars Mania

No individual better demonstrates theory-laden observation than Percival Lowell. Picking up where Schiaparelli left off, Lowell almost single-handedly brought the Mars momentum to its peak. Lowell was born into a wealthy and prominent family in Boston in 1855 and educated at Harvard in 1872 where he took mathematics and physics and was elected to the Phi Beta Kappa. After graduation, he frequently travelled to Europe and the Far East and wrote books on his travels. His writings displayed a clear talent for captivating and colourful storytelling which undoubtedly helped him win over the public imagination in his future Mars writings. During his last trip to Japan in 1892, Lowell brought along his six-inch telescope to observe the planet Saturn and his friend George Russell, a scientist from Boston. It was then that he was made aware that Schiaparelli had given up his planetary mapping due to his worsening Myopia. Lowell came back from Japan with a sudden and firm determination to build an observatory before the next Mars opposition in 1894 in order to pick up where Schiaparelli had left off. According to Hoyt:

“The fundamental motivation underlying Percival Lowell’s seemingly impulsive resolve early in 1894 to turn his energies, talents, and resources to planetary astronomy and specifically to the problem of Mars appears to have been an intellectual fascination with the possibility of the existence of extra-terrestrial life.” (Hoyt, 1976, p.55)

As Lowell was financially independent the Lowell Observatory was able to be completed less than a year later in time for the opposition. Though he was not a trained astronomer, Lowell was very thorough in his observations of Mars with a strict nightly observational routine. He kept a careful record of each observation and often published his results publicly as well as academically. He also produced a very large number of drawings of Mars with 917 of them completed in just the first year. It was during the first year as well that Lowell began recording and sketching observations of canals on the Martian surface discovering around 726 canals including geminated lines and round spots, or oases, that appeared to connect the network of canals at intervals. (Fig. 2) (Hoyt, 1976, p. 63) Interestingly very few others were able to see the canals during their observations with some of the exceptions being Lowell’s assistants at his observatory.

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Most writings about Percival Lowell, including Hoyt and Sheehan, stress that he had embarked on his study of Mars after he had already drawn positive conclusions regarding intelligent life on the planets. (Hoyt, 1976, p.68) It’s hardly surprising then that Lowell was able to find the evidence that he required in order to support his theory. Lowell’s observations of the physical conditions of Mars built the foundation that he required for canal building. He deduced that Mars had an atmosphere and that although the planet was extremely arid that it’s white polar caps must be made of water ice, although most astronomers of the time believed the caps to be made of frozen carbon dioxide.

As Schiaparelli’s and Lowell’s Martian observations had both noted seasonal changes in the Canals, and later in Lowell’s oases and polar caps, Lowell naturally concluded that as the polar caps warmed during Mars’ summer the meltwater would be channelled through the canals. The fact that the canals and the oases began to appear darker as spring swept across the planet brought him to believe that it was not the waterways themselves that were being observed but in fact the vegetation that would naturally grow to either side.

Once Lowell had established that the physical conditions on Mars were capable of sustaining life, he introduced his most remarkable theory, that that planet was inhabited by intelligent beings that were far more advanced than Earthlings. As these beings were living on a dying planet, they were engineering the canals in order to draw water from the polar caps to sustain crops and vegetation.

“That Mars is inhabited by beings of some sort or other we may consider as certain as it is uncertain what those beings may be.” (Lowell, 1906 p.376)

Once Lowell had established his formal theory, he set to work writing magazine articles and publishing books in exhaustive detail, lecturing, and giving public talks on the matter. His natural gift of storytelling, along with his charismatic personality was highly effective in capturing the imagination of the general press and public. As interest in the theory grew Mars mania exploded into the mainstream culture around the world with Martins becoming a popular theme in books and radio programmes, such as works by H. G. Wells and E.R. Burroughs.

The view taken by astronomers though was far more sceptical. Edward S. Holden, astronomer at Lick Observatory, noted: “…the conclusions reached by Mr. Lowell at the end of his work agree remarkably with the facts he set out to prove before his observatory was established at all.” (Hoyt, 1976, p.90)

Theory-laden or Neutral Observations

It is known today from NASA missions to Mars, including the Mariner Flybys and the many Mars rovers and landers that Mars does not have an intricate network of canals on its surface nor are there any signs of life, intelligent or otherwise. So, what were Schiaparelli and Lowell seeing?

Although Lowell’s canals of Mars turned out to be nothing more than fanciful conclusions, he was by no means a crackpot scientist. His observations were structured and rigorous scientific investigations. His work on spectroscopy was ground-breaking and paved the way for today’s planetary observations while his theory on the importance of atmospheric conditions in observations is now well established.

Both Schiaparelli and Lowell were probably seeing an optical illusion caused by a combination of low magnifying powers and chromatic aberration with their equipment, observing through the atmospheres of the combined planets, and the raging dust storms that are now known to envelop Mars. (Sheehan, 1998) It’s important to note that Schiaparelli was reluctant to draw any conclusions from the canals as to whether they were natural or artificial but simply recorded what he was observing, even after Lowell published his claims of extra-terrestrial life. Though they may have both observed the canals as an optical illusion it was Lowell’s interpretation of the observations that caused the Mars mania.

[bookmark: _Hlk4247371]It would be easy to argue that theory-laden observations should not be acknowledged in legitimate science, but it should be considered that theory-free or neutral observations might not progress scientific knowledge. Percival Lowell almost certainly saw what he wanted to see when observing Mars causing interest in the planet that was not necessarily there before on that level. This, in turn, increased the observations of the planet as other investigators set out to prove or disprove the existence of the canals and it brought further knowledge into the scientific community. It should also be considered that a theoretical construct may turn out to be correct.

Scientific investigation is a continuous process during which theoretical claims can be challenged.

As long as new observations are being made and new evidence is being established then the theoretical constructs are being continuously challenged or defended which will be advancing the knowledge in the scientific community. If an investigator is not pre-disposed and is solely depending on raw data or theory-free observations, then they would lack any theoretical framework in which to interpret the data or observation. Observations themselves can have little meaning or shed little light on the phenomena being observed and investigators must fall back on prior knowledge or theories in order to interpret the data. There is no one scientific method that is superior to another however and the scientific process itself shouldn’t be characterized by theory-laden or theory-free observations. Investigators should draw upon their training and knowledge of the theoretical scientific framework in order to interpret their observations and data and to distinguish which aspects of the investigation are significant.


The implications of Percival Lowell’s theory-laden observations of Mars were made clear in his books and writings. Without any formal training in astronomy, planetary observations, or the theoretical scientific framework, Lowell unknowingly allowed his social and cultural experiences to vastly influence his data and observations. Although investigators may fall back on prior knowledge or theories in their interpretations of data, without structured training and guidance it would be easy to apply one’s beliefs or prior assumptions to observations. Schiaparelli and Lowell both observed the canals on Mars but Schiaparelli, a trained astronomer, interpreted the lines as channels and chose not to speculate about their origin, while Lovell unwittingly chose to interpret the data as canals built by beings of intelligent design.


  1. Hoyt, W. G. 1976, Lowell and Mars, The University of Arizona Press
  2. Kuhn, T. 1970, The Structure of Scientific Revolutions. Chicago; The University of Chicago Press
  3. Lowell, P. 1906, Mars and it’s Canals, The Macmillan Company, Reprint 2009, Cornell University
  4. W. Sheehan. (1997). Giovanni Schiaparelli: Visions of a colour-blind astronomer. Journal of the British Astronomical Association. Vol. 107 (no. 1), p.11-15.
  5. W. Sheehan, 1998, Planets and Perception: Telescopic Views and Interpretations; 1609-1909, The University of Arizona Press

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