When Wilder Observatory was built in 1903, its telescope was one of the largest telescopes in the world at 18 inches (0.46 m). It remains one of the world's largest refractors. Built by Alvan Clark & Sons, the instrument was shipped to Chile in the summer of 1907 to observe the planet Mars when it was at opposition, a position that occurs approximately every twenty-six months. Because the Mars opposition of 1907 placed the planet low over the southern horizon from North America, it was deemed advantageous to ship a large instrument to a point south of the equator, where Mars would appear directly overhead allowing for some then state-of-the-art pictures of the red planet to be taken. Because of the extremely dry climate of the Atacama Desert, the telescope remained set up for the three-week period encompassing the opposition, without a shelter such as the dome under which it would normally be housed. Following the opposition, the telescope was then returned to its observatory at Amherst.
The objective glass blank was made by Feil-Mantois and was figured over 18 months by Carl Lundin of Alvan Clark & Sons. The dome was built by W.N. Kratzer Structural Steel of Pittsburgh, Pennsylvania. The pier and German equatorial mount was constructed by Warner and Swasey of Cleveland, Ohio. The total cost of the telescope in 1903 was $12,000, and of that the objective itself was $5,000. The observatory building was designed by the architectual firm of Mckim, Mead & White and was restored along with the telescope in 2001.