24, S. A. Hill—Observations of the Solar Thermometer. [No. 1, 
rally held by solar physicists, I have always looked upon it as doubtful, 
and probably due in part to some fortuitous combination of errors. I 
therefore intend on some future occasion, possibly after the end of the 
present year, when the position of the thermometer at Allahabad will be 
changed, to go over the figures again, taking a longer series of obser- 
vations and making allowance for a cause of variation from month to 
month, namely, the elliptic form of the earth’s orbit, which was neglected 
in the paper referred to. Meanwhile, I wish to lay before the Society the 
results of some other observations bearing on the same question, which 
tend to confirm the conclusions arrived atin my previous paper. To the 
method by which these results are attained, less exception can be taken, 
because they are in every case derived from several observations made 
on the same day under different degrees of obliquity of incidence, in- 
stead of upon the single record of a self-registering instrument. 
Shortly after hourly observations on four days in each month were 
commenced at Lucknow, it was discovered that the solar thermometer 
in use at that station had ceased to be self-registering. A new instru- 
ment was therefore brought into use on ordinary days, but the old one 
was retained for the hourly observations. The records of all such obser- 
vations of this instrument since the middle of the year 1876 have been 
filed, but for the purposes of the present paper I have used only those 
of the eight years 1877—1884 inclusive. At Agra, similar observations of 
a non-registering solar thermometer have been made for some years on 
hourly observation days, but, owing to a change of instrument, the 
register for the years 1877—1884 is broken. For this reason, and because 
the observatory at Agra is situated in the midst of the city, I have not 
thought it worth while to reduce the registers of that station, though 
they seem to confirm in a general way the results obtained from Luck- 
now. 
Those parts of the Lucknow records which have been used for the 
purposes of the present paper are printed in Table I. The figures represent 
for each hour of observation the difference between the temperature of 
the black-bulb thermometer in the sunshine and the simultanecus tem- 
perature in the shade. Only those hours are given at which the sky 
was either quite free from cloud or at which the cloud proportion did 
not exceed 2-10ths of the expanse. In the months of July and August, 
very few clear days, thus defined, occur; consequently these months 
have been left out in drawing up the tables. For every other month in 
the eight years, except September 1878 and June 1880, there are some 
observations available. 
