70 Linnccan Society. 



" 3. Two ocular irradiations near one another, which tend to act in 

 a contrary direction, and to encroach upon each other, mutually de- 

 stroy each other, and the more completely the nearer they are made 

 to approach. 



" 4. Ocular irradiation varies considerably in different persons. 



"5. In observations made through astronomical glasses, that part 

 of the total error which arises from ocular irradiation is dependent 

 upon the enlargement on the brightness of the image, and on the 

 greater or less degree of sensibility of the eye of the observer for 

 irradiation. 



"6. This part of the total error necessarily vanishes in observations 

 where a double image micrometer is used. 



" 7. The part of the total error attributable to the aberrations of 

 the glass necessarily varies with different instruments, but for the 

 same glass it may be considered as constant, that is to say, inde- 

 pendent of the magnifying enlargement. 



" 8. The irradiation in glasses, or the total error arising from the 

 ocular irradiation and from the aberrations of the instrument, is ne- 

 cessarily variable, since it depends upon variable elements." 



XV. Proceedings of Learned Societies. 



LINNiEAN SOCIETY. 

 [Continued from vol. xiv. p. 463.] 



March 5. — "DEAD, "Observations on some Fungi or Agarici, 

 -■- *' M'hich by deliquescence form an inky fluid, drying 

 into a bister-coloured mass, capable of being used as a water-colour 

 for drawings, and of a very indestructible nature by means of common 

 agencies." By John Redman Coxe, M.D., formerly Professor of 

 Materia Medica in the University of Pennsylvania. Communicated 

 by the Secretary. 



Dr. Coxe having gathered a Fungus and placed it on a sheet of 

 white paper, leaving it until the next day, found several drops of an 

 inky fluid, slowly trickling from the inner surface, which had as- 

 sumed a black appearance ; by placing the Fungus in a glass, the 

 whole except the outer skin liquefied. The colour of the fluid was 

 rather a deep bister than black, and being left in the glass, in a few 

 hours it separated into a solid sediment, with a lighter coloured fluid 

 swimming above. Having afterwards collected a considerable quan- 

 tity of fluid from the same species, he obtained by drying an extract 

 of a pretty deep black colour of both parts conjoined, which would 

 otherwise have separated. This on trial formed an admirable bister- 

 like water-colour, well adapted for drawing when mixed with a little 

 gum. 



Dr. Coxe used the " fresh inky fluid as ink, and from such fresh 

 fluid the accompanying drawings were made ;" but it was soon found 

 that its change was too rapid to think of depending on it for such a 

 purpose, he therefore was led to dry it as quickly as possible by 

 spontaneous evaporation, and then to use it diluted with water. 

 Having exposed various portions of writing thus made to the direct 

 rays of the sun for several months with little change, he tried the 

 effects of chlorine and euchlorine gas, muriatic acid, and ammoniacal 



