1866. | De la Rue and Celestial Photography 369 
and which is therefore of no common interest to the inquiring 
mind. 
Upon the occasion of Mr. De la Rue’s visit to Rome, an attempt 
was made, as a secondary object, by comparing the distances of the 
moon’s and sun’s centres with the tabular places, to ascertain 
whether any correction was necessary to the sun and moon’s tabular 
diameters ; and it was found that the latter were in excess of the 
observed diameters. The correction assigned to the moon’s radius 
from two sets of the observations has been recently computed to be 
2'-15, which agrees closely with the correction Mr. Airy has found 
to be necessary from M. Breins’ reductions of forty years’ observa- 
tions of disappearances and reappearances of stars at the moon’s 
dark limb durimg occultations.* 
From 1860 to the present time, the observations by the Kew 
heliograph have been placed by the Council of the Royal Society 
under Mr. De la Rue’s direction. From February, 1862, to February, 
1863, the instrument was removed to the Observatory at Cranford, 
but a qualified assistant having been trained for the Kew Obser- 
vatory during that interval, it has been worked continuously at that 
establishment from May, 1863, until the present time. 
The object in view is, of course, to obtain the most perfect 
record possible of all the physical changes which take place on the 
sun. “The progress of science,” says Mr. De la Rue,f “ has hitherto 
only shrouded in deeper mystery than ever the origin of that won- 
derful outpouring of light and heat which is the sun’s most promi- 
nent characteristic; and to this very day it has not been finally 
decided whether this luminosity proceeds from the sun’s solid body, 
or from an envelope which surrounds it. Indeed, so strange and 
so unaccountable are many of the features presented to us, not only 
by our own sun, but by many of the stars, that it has even been 
conjectured that these bodies exhibit imstances of the operation of 
forces, of the nature of which we are yet ignorant. If we accept 
this view of the case, the study of our luminary becomes one of very 
great importance, but one in which we must be very careful to be 
guided by observation alone. We must obtain numerous and accu- 
rate representations of the sun’s surface, and study these carefully 
and minutely before we attempt to generalize.” 
In the ‘Researches’ from which we have quoted, we find 
recorded no less than 631 groups of solar spots, which have been 
ce erhed at the Kew Observatory from March 11, 1858, to 
ecember 31, 1864. The value of such a continuous record as this 
can only be thoroughly understood by those who have given some 
* ‘Monthly Notices of Astronomical Society,’ vol. xxv., p. 264. 
+ ‘Researches on Solar Physics. By Warren De la Rue, F.R.S., Balfour 
et F.R.S., and Benjamin Loewy. (First Series, “On the Nature of Sun 
pots.”) 
