1866. ] De la Rue and Celestial Photography. 871 
temperature than the photosphere in which it is formed. Whether 
this is due, as some suppose, to the lower temperature of the body 
of the sun, or to matter coming from a colder region, as is more 
generally thought, remains yet to be determined. 
Chacornac and Lockyer have recorded observations, on the 
behaviour of the matter surrounding a spot, which appear to suggest 
the existence of a downward current, which is, therefore, a current 
from the colder regions above. The facule in the larger number 
of examples fall behind the spots. This appears to suggest an 
ascending current carrying the hot matter behmd. Thus possibly 
two currents are concerned in the formation of a sun spot; if so, 
assimilating them to our terrestrial cyclones, which in many other 
respects they resemble. 
The importance and the extension of this system of continuous 
observation must be evident to all; and it is satisfactory to know 
that a second heliograph has been made under Mr. De la Rue’s 
direction for the Russian Government, which is now erected at 
Wilna, the director of that observatory, Dr. Sabler, having received 
instruction at Mr. De la Rue’s observatory at Cranford. 
On several occasions, at the Astronomical Society, Mr. Warren 
De la Rue has pointed out the advantages which will be derived 
from the use of photographic apparatus for recording future transits 
of Venus. In the words of the address on the presentation of the 
Lalande prize, we may bring our notice of Celestial Photography to 
a conclusion :—“ By his own example, by giving instruction to 
others who desired it, and by continuous observations of his own, 
Mr. Warren De la Rue has been untiring in promoting astronomical 
photography ; and it may be safely claimed for him that the bringing 
of this branch of science within the domain of calculation, marks a 
new era in practical astronomy.” 
