371 



which necessarily caused both a diminution of the light and also a 

 diminished sensitiveness of the collodion film. 



The rapidity with which the above pictures were taken may be 

 better understood by comparing them with those of terrestrial objects 

 under similar circumstances. According to Herschel* 



" The actual illumination of the lunar surface is not much superior 

 to that of weathered sandstone rock in full sunshine. I have fre- 

 quently compared the moon setting behind the grey perpendicular 

 fa$ade of the Table Mountain, illuminated by the sun just risen in 

 the opposite quarter of the horizon, when it has been scarcely distin- 

 guishable in brightness from the rock in contact with it. The sun 

 and moon being nearly at equal altitudes, and the atmosphere per- 

 fectly free from cloud or vapour, its effect is alike on both lumi- 

 naries." 



Thus by comparing the Liverpool object-glass as to power with 

 our ordinary camera lens, its focal length being nearly 19 times the 

 aperture, and the moon's image being copied by its means in 4 

 seconds, we find that it is equivalent to copying sandstone illuminated 

 by the sun in 4 seconds with a lens 4^ inches focus and a little less 

 than | inch diaphragm ; or with a compound lens having an aperture 

 of one inch, and the same focal length, in a quarter of a second. 



II. " Researches on the Reproductive Organs of the Annelids/' 

 By THOMAS WILLIAMS, M.D., F.L.S., Physician to the 

 Swansea Infirmary. Communicated by THOMAS BELL, 

 Esq., F.R.S., P.L.S. &c. Received December 30, 1856. 



(Abstract.) 



In this paper the author seeks to establish the following general 

 proposition, viz. that there prevails throughout the Actiniadse, Echi- 

 nodermata, Rotifera and Annelida, a special organ, which, under 

 different phases, subserves different functions, which is essentially 

 identifiable under every modification, reducible to the same type, and 

 which constitutes the root of the Reproductive system in these fami- 

 lies. To this special organ he proposes to apply the provisional 



* Ilerschel's Outlines of Astronomy, page 249. 



