found a suitable pair of optical discs in New York. He figured both pairs, 

 and with them he discovered eight new double star systems. 59 He brought 

 both finished objectives and one equatorial mount with him when he 

 visited Dawes in 1859. 60 Both objectives were so fine that Dawes was 

 puzzled to decide which to keep. 61 He finally sold the 8-inch aperture 

 American glass, with the equatorial mount, for £500, and the Clarks sent 

 him another mount for the 8j4-inch lens. The 8*4 -inch was sold, in 

 1864, to Rev. R. E. Lowe (q.v.), who, seven years later, sold it to J. M. 

 Wilson of Rugby School, (q.v.). The definition of this object glass was 

 declared, by Otto Struve, to be superior to that of the Dorpat and Pul- 

 kowa instruments. 62 



Heretofore Dawes had known the Clarks only as opticians and astro- 

 nomical observers. His decision to replace his Munich equatorial mount 

 with one made by the Clarks was prompted by the Bonds" enthusiastic 

 report of the performance of the new clock drive they had made for the 

 Harvard equatorial (q.v.). 63 



The Clarks' cast iron mount was so firm, compact, and elegant Dawes 

 thought fit to describe it to the Royal Astronomical Society. 64 The tube 

 was supported by the open ends of a movable arc structure which served 

 as the polar axis. The intervening semicircular space held most of the 

 wheelwork of the driving clock. Since the arc slid in a groove in the 

 lower part of the mount, the polar axis could be easily adjusted for any 

 latitude. With this mount, as opposed to one of the German form, stars 

 could be followed continuously as they crossed the meridian. The motion 

 of the driving clock, nicely regulated by a half seconds pendulum and 

 a spring governor, was so equable that, even with high powers, Dawes 



59 William R. Dawes, "New Double Stars Discovered by Mr. Alvan Clark," 

 Monthly Notices, Royal Astronomical Society, vol. 20 (1859), p. 55. 



60 Simon Newcomb, "The Story of a Telescope," Scribner's Monthly, vol. 7 (1873- 

 1874), p. 46. 



61 William R. Dawes to George Knott, 15 August 1859 (letter published in 

 Observatory, vol. 33 [19 10], pp. 352-353). 



62 William R. Dawes to R. E. Lowe, 20 June 1864 (letter in Rugby School 

 Archives) . 



« William R. Dawes to William C. Bond, 30 June 1857 (letter in Bond Papers. 

 Harvard University Archives). 



fA William R. Dawes, "Description of an Equatorial Recently Erected at Hope- 

 field Observatory, Haddenham, Bucks," Monthly Notices, Royal Astronomical Society, 

 vol. 20 (1859-1860), pp. 60-62. 



53 



