president's address — SECTION A. 75 



F.R.A.S., whom I have already quoted, was very busy tryinj? to take 

 photographs with what must have been in those days a very large 

 instrument. The Craigh telescope, at Wandsworth, Avhich he used, 

 had a diameter of 2ft. and a focal length of 77ft. It is not stated 

 whether it was a refractor, but " the true photogenic focus was 

 difficult to find," and he goes on to say, "that so large an object 

 glass worked by hand should do so much with the stars is far from 

 discreditable.'"' He then speaks of reworking the surfaces of the 

 object glass, which seems to leave no doubt that it was not a 

 reflector, which has one surface only. With such a long focus the 

 moon's image should be nearly Sin. in diameter; the time of 

 exposure for a collodion picture of the moon was thirty-five seconds. 

 This telescope was not equatorially mounted, and the moon's 

 apparent motion when near the meridian was counteracted by a 

 •' screw motion given to the eye end of the telescope"; the rate was 

 guided by looking through the collodion at a crater kept on crot^s 

 wires; from a negative taken on September 6th, 1854, a negative 

 9in. in diameter was made, which was compared with one taken by 

 Bond at Harvard Observatory, and Mr. Reade adds, "in this photo- 

 graph all the more important features of the moon's surface will 

 be discovered by those who are familiar with their telescopic 

 appearance." I have already quoted his comparison of his photo- 

 graph with the Bond photograph. 



In 1857 Professor Henry Draper'**, after seeing Lord Rosse's 

 great reflector, returned to America with his mind made up to con- 

 struct a large reflector and use it for astronomical photography. He 

 made a metallic reflector 15^in. diameter and I2it. focus, but soon 

 discarded it for a silvered glass one of same size and r2ft. 6in. 

 focus.'' He made 1,500 photographs of the moon with it, of which 

 the best was made September 3rd, 1863, and was enlarged to 3ft., 

 the original being 1-Ain- diameter. In 1857 Bond'-, having sup- 

 plied the driving clock of the equatorial with the spring governor 

 which he had invented, again turned his attention to photography, 

 and by the aid of the more rapid collodion plates took photographs 

 of stars of various magnitudes up to the sixth ; the brighter star 

 of Zeta Ursee Majoris recorded itself in two seconds and the 

 companion in eight seconds. Measures were made of these, and in 

 this early stage it was found that the probable error of a single 

 measiu'e of the distance between them was only + 0'12". Star 

 pictures were made soon afterwards by Mr. De La Rue and Mr. 

 Rutherford, at the meeting of the Royal Astronomical Society on 

 November 1 3th, 1857. Mr. Airy, the Astronomer Royal, exhibited 

 Bond's photographs of this double star, Zeta Ursse Majoris, and used 

 these memorable words — " This photoi;ra[)h marks a step of very 

 great importance which has been i^iade, of which either as regards 

 the self-delineation of clusters of stars, netailaj, and planets, or as 

 regards the self-delineation of observations, it is impossible at 

 present to estimate the value." Mr. Bond had, in 1857, obtained 



