46 
-observations of solar radiation were anomalous and unsatis- 
factory. It may, therefore, be necessary to state that these 
observations appear to have been made under circumstances 
not favourable to the accurate determination of the intensity 
of solar radiation at all seasons of the year. The values 
derived from them appear to be too high in summer, and 
too low in winter. Take, for instance, any winter month, 
say December, 1857. The* mean differeuce for the month 
between the maximum in sun and the maximum in shade 
was only 1*7° : at Oxford, it was* 6T°. The highest value 
during the month was 4*5° at Greenwich : at Oxford, it was 
19*0°. At Greenwich there were only seven days on which 
the difference exceeded 30°:; at Oxford there were seven- 
teen. And yet at Greenwich the month was unusually fine 
and dry, only 0*36 of an inch of rain fell, and several days 
appear to have been nearly, if not quite, cloudless. Under 
these circumstances, it is difficult to understand why the 
black-bulb thermometer, if properly exposed, did not register 
much greater differences. In 1859 there was a remarkable 
and unaccountable falling off in the summer values, and the 
mean for the year was decidedly lower than the mean of 
any of the three preceding years; but at Oxford it was 
higher. I can only account for this remarkable difference 
by supposing that some change was made in the position of 
the solar radiation thermometer at Greenwich in the early 
part of the year. 
From the beginning of 1860 to the end of 1864 the obser- 
vations at Greenwich were made with a black bulb ther- 
mometer in vacuo, and it is satisfactory to find that the 
course of the annual means is in tolerably fair agreement 
with that of the results obtained at Oxford with the ordinary 
black bulb thermometer. 
“Solar Radiation Observations, made at Old Trafford, 
Manchester,” by G. V. Vernon, F.R.A.S., F.M.S. 
Mr. J oseph Baxendell, F.R A.S., having at a recent meet- 
