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VIII. On the Corrections to be applied to the Monthly Means of Meteorological 
Observations tahen at any hour, to convert them into Mean Monthly values. 
By James Glaisher, Esq., of the Royal Observatory at Greenwich. 
Communicated by G. B. Airy, Esq., F.R.S, 8$c., Astronomer Royal. 
Received February 23 , — Read March 2, 1848. 
One of the most useful results of observations made at short intervals during the 
day and night, and continued for several years, is the knowledge we thus obtain of 
the diurnal ranges of the different subjects of investigation, and consequently the 
difference between the mean values of each element, as deduced from observations at 
one or more hours daily, and the true mean for the period over which the observa- 
tions are spread. 
At the Royal Observatory at Greenwich magnetical and meteorological observa- 
tions have been taken since the year 1840, as is familiar to the Fellows of this Society. 
These have been published to the end of the year 1845. The whole of these observa- 
tions have been made under my immediate superintendence, under the direction of 
the Astronomer Royal, and I believe that no observations have been made and reduced 
with greater care or regularity. As the person entrusted with the superintendence 
of these operations, I have a more perfect knowledge of them than any other person 
can have ; I feel it therefore a duty to communicate their results from time to time, 
when the doing so promises to be of essential service in promoting the advancement 
of the subjects of investigation. 
I have selected for my present communication some results deduced from the me- 
teorological observations, and I have preferred these to the magnetical, not only on 
account of the greater accordance in the results year by year, but also because of 
their more immediate and general use. At the present time I believe that there are 
a greater number of persons engaged on meteorological researches upon a systematic 
plan, than have hitherto been so engaged, but, necessarily, these persons can observe 
only at certain times convenient to themselves, and these times differ from each 
other. To render their results comparable, it is necessary to apply corrections to 
every different result depending upon the time, or times of the day at which the ob- 
servations have been made. 
The barometrical and thermometrical observations treated of in this paper have 
been made at every even hour of Gottingen mean solar time, throughout each of the 
five years, except on Sundays, Good Friday and Christmas day; the mean of each 
hour represents the results deduced from about 150 observations; those for each 
