577 
which have hitherto been given of this difficulty, and quotes, on 
this point, the authority of Sir John Herschel. It then proceeds to 
prove, both theoretically and by observation, the existence of a slow 
downward current of air mingled with minute globules of water, the 
current itself being the effect of the rain, and originating in the 
cloud from which the rain proceeds. The twofold agency of this 
downward current in producing the paradoxical results is then ex- 
plained ; and the paper concludes with a numerical estimate, the 
object of which is to prove that the quantity of water which it is 
necessary to assume as being contained in a given volume of the 
atmosphere, at a given time , in order to account for even the more 
remarkable results on record, is too small to give rise to the appear- 
ance of cloud ; and so, by proving this, to obviate what would other- 
wise have been a formidable objection to the proposed explanation 
of the phenomenon. 
4. On the Structure of the Bark of Araucaria imbricata, with 
special reference to Palaeontology. By John Hutton Bal- 
four, A.M., M.D , F.R.S., Sec. R.S.E., Professor of Medicine 
and Botany. 
The frost of December 1860 caused serious damage to trees and 
shrubs in the Botanic Garden of Edinburgh. On the morning of 
24th December, Fahrenheit’s thermometer stood at 6° below zero, 
according to the Kew standard. An account of the injury inflicted 
has been already published in the Transactions of the Botanical So- 
ciety of Edinburgh. It has been stated that the great cold in 
the garden, as compared with other places near Edinburgh, may be 
accounted for by its low sheltered situation, and the descent of the 
heavy cold atmosphere from the more elevated localities around. 
Among the plants which suffered were two very fine specimens 
of Araucaria imbricata , which had stood for upwards of thirty years, 
and one of which had attained the height of 24J feet, with a cir- 
cumference of 4 feet at the base of the stem, and with twenty 
whorls of branches. These trees, which were great ornaments of 
the lawn in front of the range of hothouses, have been cut down. 
An opportunity was thus afforded of examining the structure of 
their wood and bark. The former is very hard and heavy, and 
promises to be valuable timber. In regard to the latter, the scars 
