370 



were well and carefully washed in warm water, dried before a fire, 

 and, after scratching the description or name on a corner, varnished 

 with the usual solution of amber in chloroform. 



The subsequent operation of printing is so easily performed, and 

 has been so fully described by persons of more experience than my- 

 self, that any further allusion to it will be needless. 



Appendix. 



Besides the pictures taken in America which are almost valueless 

 as moon maps, as the sides are reversed in the copying from the 

 daguerreotype plate upon which they were originally taken, the 

 moon has been photographed by Professor Phillips, Father Secchi, 

 MM. Bertsch and Arnauld, several Liverpool photographers, and 

 Mr. Hartnup and myself. It is interesting and instructive to 

 compare among themselves the means employed and the time occu- 

 pied in taking the impression on these several occasions. 

 ;. Professor Phillips's telescope has a sidereal focus of 1 1 feet, and 

 an aperture of 6| inches; consequently the brilliancy of the moon's 

 image in its focus is augmented 26 times over what she appears to 

 the naked eye. The average time occupied for the collodion plate 

 to receive the impression was about 3 minutes. 



Father Secchi' s telescope having a sidereal focus of 18 times its 

 aperture, the moon's image was intensified 37 -8 times, and the time 

 required for the impression was an average of G minutes. 



M. Porro's glass of 49 feet sidereal focus and 20 inches aperture, 

 gave a moon image 12-3 times brighter than she appeared to the 

 naked eye, and the average time of taking the picture was 17 

 seconds. 



Mr. Hartnup' s telescope being 12| feet focus and 8 inches aperture, 

 augments the intensity of the moon's image at its focus 35'1 times. 

 The time which was required for the photograph of our satellite to be 

 taken, on the occasion of the meeting of the British Association 

 at Liverpool in 1854, was about 2 minutes ; and under the same 

 circumstances we ourselves succeeded in obtaining perfect and intense 

 negatives in 4 seconds. These, however, were taken under very 

 unfavourable circumstances, the temperature being below the freezing- 

 point, and the moon at a considerable distance from the meridian, 



