513 



Having always found in the South American guano more distinct 

 traces of lithate of ammonia than in the African, he inquires 

 whether the difference may not be owing to different states of 

 atmosphere in the two regions ; — in the one, the clouded state of the 

 air impeding the sun's rays ; in the other, the usually unclouded 

 state interposing no obstacle to their full effect. He inquires too, 

 whether the circumstance of the comparatively rapid conversion of 

 lithic acid into the oxalic under the influence of light, as witnessed 

 in the experiment detailed, may not account for even recently 

 formed guano being destitute of lithate of ammonia; and he men- 

 tions an example in point, namely, a specimen he had received from 

 the island of Ichabor being found with a large quantity of oxalate 

 of ammonia, to contain no lithate of ammonia, — a specimen described 

 as " having been scraped off" a rock, where it was in a thin layer, 

 and much exposed to the sun." 



2. " An Account of the Newtonian Dial presented to the Royal 

 Society, in a letter to the President." By the Rev. Charles Turnor, 

 F.R.S. 



The dial here described was taken down in the early part of the 

 present year from the south wall of the Manor-house of Wools- 

 thorpe, a hamlet to Colsterworth in the county of Lincoln, the 

 birth-place of Newton. It was marked on a large stone at the angle 

 of the building, and about six feet from the ground. The name of 

 Newton, with the exception of the first two letters, which have 

 been obliterated, are inscribed under the dial in wide and capital 

 letters. The gnomon has disappeared many years ago. 



3. " On the Non-coincidence of the Focus of the Photogenic Rays 

 with that of the Visual Rays of the Solar Spectrum." By M. A. 

 Claudet. Communicated by S. Hunter Christie, Esq., Sec. R.S., &c. 



After detailing the difficulties he had met with in obtaining per- 

 fect pictures when a lens, accurately corrected for spherical and 

 chromatic aberration, was employed in the Daguerreotype process, 

 the author states that in order to obtain a clear and well-defined 

 image of any object on the Daguerreotype plate, he generally found 

 it necessary to adjust the focus on the ground glass by another ob- 

 ject brought considerably nearer to the camera than the object 

 whose picture was required. When this adjustment is made, he 

 proceeds to apply the principle practically to the taking of portraits. 

 He finds that in achromatic object-glasses the focus of photogenic 

 action is not coincident with the visual focus ; and the distance be- 

 tween these two foci varies according to the nature of the combina- 

 tion of the glasses, to their diff'erent dispersive powers, and to the 

 degree of intensity of the light. By attention to these circumstances 

 in accurately adjusting the Daguerreotype plate to the situation of 

 the focus of the photogenic rays, the author has succeeded in ob- 

 taining the most perfect delineations of objects. 



4. " Observations on some of the Nebulae." By the Earl of Rosse, 

 FR.S. 



