70 Cambridge Philosophical Society. 



precipitation of water from the atmosphere, &c. The third theory is 

 that of the independent equilibrium of vapour in air, maintained by 

 DeLuc, but fully developed and established by Mr. Dalton. — The 

 stumbling-block of all the other theories is, that at a given tempera- 

 ture the same quantity of vapour exists in a given space, whether 

 the air be dense or rare, or if there be none at all. The use of the 

 devo point in determining the tension of this vapour was shown, and 

 the application of Daniell's hygrometer to this purpose was explained. 

 The formation oi cumulus by the rise of a warm vaporous stratum 

 into a colder region above was noticed, and illustrated by cases in 

 which, in a mountainous country, we see, considerably above the 

 tops of the hills, a mass of cumulus over each eminence, while the air 

 on the intermediate lower spaces is cloudless : the vapour being 

 carried up the slopes of the hills, and thus thrown into the region 

 of condensation above their summits. 



Dec. 12. — The reading of Prof. Henslow's paper was concluded. 



The object of this paper was to give the detail of an examination 

 of a hybrid between I), purpurea and D.lutea, accidentally pro- 

 duced in the garden of the author. — The account is to be accom- 

 panied by four plates : the first containing a figure of the raceme 

 and radical leaf of the hybrid ; the second presenting a comparative 

 view of the various parts of its organs of fructification, with the 

 corresponding parts in those of the parents ; and showing the ex- 

 actly intermediate character which most of the former possess in 

 size, shape, and colour to those of the latter. The only very re- 

 markable exceptions to this rule are found in the pollen and ovules, 

 each of which, by measurement with the micrometer, prove to be 

 of precisely the same dimensions in all the three. The shape of 

 the stigma also forms another exception. The pollen of the hy- 

 brid was, for the most part, imperfect, and its ovules proved barren 

 in every instance, even though some of the stigmas were touched 

 with the pollen oi purpurea, and others with that of lutea. 



The examination of the internal structure of the organs of fructi- 

 fication is detailed in the two remaining plates; and so far as it was 

 prosecuted, furnished no appreciable difference either in the nutri- 

 tive or reproductive apparatus of the three flowers. A few new or 

 otherwise interesting circumstances connected with the general 

 anatomy of these organs were described; the most important of 

 which appear to be, the observation of a central nucleus in the 

 vesicles of the epidermis, and the delicate investing membrane to 

 the same organ marked with faint parallel strias. The possibility 

 of separating the vascular bundles into from thirty to fifty distinct 

 tracheae was also recorded ; and the mode in which the stigmatic 

 tissue meets the placenta by investing its surface, was pointed out 

 as the probable result of repeated experiment. 



A lecture was given by C. Jenyns, Esq. On the Principles of the 

 Perspective of Shadows. 



ROYAL 



