and Hit deposition of Dew. 259 
and the second, when, by the interposition of dense clouds, the 
temperature of the land is raised, and which, by imparting its 
influence to its superincumbent air, restores it to a temperature 
equal to, or even greater than that of the atmosphere reposing 
on the water, ultimately causing the mist to disappear, from the 
increased capacity of the air for vapour. This latter circum- 
stance will also account for the dispersion of mists in the mor- 
ning, before the disappearance of dew. 
The gentle motion that must also take place, from the ming- 
ling of the cold air from the land with the warmer air above 
the water, will have a tendency to increase the deposition of 
dew, since new volumes of air will be successively brought into 
contact with the cold surface of the earth, and which, by depo- 
siting their moisture, will augment the quantity of dew beyond 
what would otherwise have been formed, had the atmosphere 
remained perfectly calm. Dr Wells found, that a slight agita- 
tion of the air was always accompanied with an increase of dew. 
The general tenor of these observations is in some degree 
confirmed by a remark of the same indefatigable observer, that 
u dew is always very copious on those clear and calm nights 
which are followed by misty or foggy mornings.” 
Pl VMOUTH, ) 
July 10. 1823. J 
Art. XI . — Description of Five New Genera of Plants, belong- 
ing to the Natural -Order Bignoniacea. By Mr David Don,. 
Librarian to the Linnean Society, Corresponding Member of 
the Wernerian Natural History Society &c. 
Among the numerous tribes of vegetables which people the 
vast regions of equinoctial America, the Bignoniacea hold a dis- 
tinguished rank, whether as regarded for the beauty of their 
flowers and the diversity of their forms, which give to the vege- 
tation peculiar features, or as objects highly deserving the atten- 
tion and investigation of the botanist. Perhaps in no tribe of 
plants, does the form of vegetation assume such variety as in 
this extensive family. In the beautiful genus Jacaranda 
are 
Read before the Wernerian Natural History Society, 23d April 1823, 
R 2 
