putedly a model for the Lick telescope, was used photographically. This 

 instrument was in use by the summer of 1894. 157 



Hoping to confirm the revelations of the 1894 Martian opposition, 

 Percival Lowell planned to observe the next close approach of Mars 

 under even more favorable conditions. Accordingly, he ordered a 24-inch 

 equatorial refractor from the Clarks. Because of the astronomical dead- 

 line this instrument was constructed in less than a year. Nevertheless, 

 this last large and complete telescope built by Alvan Graham was ex- 

 ceptionally perfect. When the lively aspects of the planets seen through 

 it by the Lowell observers, and unconfirmed elsewhere, led E. S. Holden 

 to suggest the Lowell lens was improperly held in its cell, Alvan Graham 

 publicly defended the perfection of the telescope. 158 The glass discs, 

 cast by Mantois, were particularly pure. To figure them the Clark 

 opticians used glass forms- — or tools — rather than the customary metal 

 ones. 159 The result was such that, according to Dr. Hartmann himself, 

 the elimination of the residual spherical aberration was more complete 

 than in any lens yet tested. 160 The Bumham-type micrometer showed 

 uniformly bright threads against a perfectly dark field. And the mount 

 was said to be "by far the heaviest and strongest ... of any telescope 

 of this size in the world." 161 



In 1909 Carl Lundin, then of the Alvan Clark & Sons Corporation, 

 figured a 42-inch Newtonian reflector for Lowell. The mirror was in 

 continuous use for half a century, until it was broken while being con- 

 verted to a Cassegrain. 



Percival Lowell seems to have been a friend as well as a customer of 

 Alvan Graham's. In December 1895 the two men went together to Paris 

 to visit astronomical acquaintances. 162 The following July they went 

 together to Arizona to set up and test the 24-inch telescope. And a week 



157 Andrew E. Douglass, "The Lowell Observatory and Its Work," Popular 

 Astronomy, vol. 2 (1894-1895), pp. 395-397. 



158 Alvan Graham Clark, letter to the editor, Science U.S., vol. 5 (1897), p. 768. 



159 "Another Large Telescope," Scientific American, vol. 73 (1895), p. 230. 



i6o v. M. Slipher, "The Lowell Observatory," Publications, Astronomical Society of 

 the Pacific, vol. 39 (1927), pp. 144-145. See also Gerhard R. Miczaika and William 

 M. Sinton, Tools of the Astronomer (Cambridge, Mass., 1961), p. 61. 



161 Thomas J. J. See, "A Sketch of the New 24-inch Refractor of the Lowell 

 Observatory," Popular Astronomy, vol. 4 (1896-1897), pp. 297-300. 



162 A. Lawrence Lowell, Biography of Percival Lowell (New York, 1935), pp. 92-95. 



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