The
Ramanujan–Soldner constant and the
Soldner coordinate system are named for him. The latter was used until the middle of the 20th century in Germany. In 1809, Soldner calculated the
Euler–Mascheroni constant's value to 24 decimal places. He also published on the
logarithmic integral function. ;Light bending Soldner is now mostly remembered for having concluded — based on
Newton's
corpuscular theory of light — that light would be diverted by heavenly bodies. In a paper written in 1801 and published in 1804, he calculated the amount of deflection of a light ray by a star and wrote: "If one substitute into tang ω the acceleration of gravity on the surface of the sun, and the radius on that body is set to unity, one finds ω=0,84". Soldner already noted that if it were possible to observe fixed stars in close distance to the Sun, it might be important to take this effect into consideration. However, because (at that time) such observations were impossible, Soldner concluded that those effects can be neglected. Soldner's work on the effect of gravity on light came to be considered less relevant during the nineteenth century, as "corpuscular" theories and calculations based on them were increasingly considered to have been discredited in favour of wave theories of light. Other prescient work that became unpopular and largely forgotten for similar reasons include possibly
Henry Cavendish's light-bending calculations,
John Michell's 1783 study of gravitational horizons and the spectral shifting of light by gravity, and even
Isaac Newton's study in
Principia of the gravitational bending of the paths of "corpuscles", and his description of light-bending in
Opticks.
Albert Einstein calculated and published a value for the amount of gravitational light-bending in light skimming the Sun in 1911, leading
Philipp Lenard to accuse Einstein of
plagiarising Soldner's result. Lenard's accusation against Einstein is usually considered to have been at least partly motivated by Lenard's
Nazi sympathies and his enthusiasm for the
Deutsche Physik movement, although it must be pointed out that Nazis were not around in 1911. At the time, Einstein may well have been genuinely unaware of Soldner's work, or he may have considered his own calculations to be independent and free-standing, requiring no references to earlier research. Einstein's 1911 calculation was based on the idea of
gravitational time dilation. In any case, Einstein's subsequent 1915
general theory of relativity argued that all these calculations had been incomplete, and that the Newtonian arguments, combined with light-bending effects due to gravitational time dilation, gave a combined prediction that was twice as high as the earlier predictions. ==References==