The 30-Inch Refractor

Abstract

After Otto’s death, his friend and long-time colleague Magnus Nyrén wrote of him to the effect that he had taken his father’s creation (i.e. Pulkovo) and raised it to a double height.¹ In one respect this was literally true: Wilhelm had endowed Pulkovo with a 15-inch refractor, Otto provided it with one of 30 inches aperture. At the time of the celebration of Pulkovo’s fiftieth anniversary, Otto wrote an official description of the acquisition of this large telescope.² His letters to Newcomb, Gill and Abbe provide a less formal account and allow us to follow the development of the project with the many difficulties that Otto encountered at the time. Newcomb’s influence was particularly important --he himself claims to have suggested that the firm of Alvan Clark and Sons might grind and polish the great lens- and Otto made clear from the beginning that Newcomb’s opinion carried great weight with him. Otto first broached the matter to Newcomb in a letter written in March 1879. He explained that it had been Wilhelm’s deliberate policy to provide Pulkovo with the most powerful refractor in the world --just as earlier he had done for Dorpat. The original 15-inch had been equalled by Harvard, however, and now surpassed by Washington. Indeed, an equal to the Washington telescope was even then under construction in Vienna. It troubled Otto that Pulkovo should thus be dethroned from the position his father had envisaged for it, but he made no approach to the government until after the end of the Russo-Turkish war of 1877-8, when he proposed the construction of a refractor of 30 to 32 inches aperture for Pulkovo because

…according to an investigation by Mr. Simon Newcomb these dimensions form nearly the limit beyond which not considerably more for “space penetrating power” [English phrase in a German letter] can be obtained. Of this your speculation, unfortunately nothing else is known to me than what is said in a notice of your Popular Astronomy in the Monthly Notices (I have not yet set eyes on the book itself). It would interest me much, therefore, to learn whether even now you are still of this opinion.⁴