126 
MR. GLAISHER ON THE CORRECTIONS TO BE 
month represents about 1800 observations ; and those for the year represents upwards 
of 21,000 observations of each element. The hygrometrical observations were not 
commenced at so early a period as those of the barometer and thermometer ; and 
each of the following yearly tables, relative to the hygrometrical states of the air, 
represents about 20,000 simultaneous observations of the dry- and wet-bulb thermo- 
meters. 
The method of formation of the tables was as follows : — 
The first step was the formation of tables representing the excess of the mean value 
of eaeh element at every hour of observation, in every month, above the mean value 
for the month. 
The second step was the formation of tables containing the numbers found in the 
first process, arranged for the different years. The accordance of these numbers for 
the different years was found to be very close indeed. 
The third step was the taking the mean of the numbers in the second set of Tables, 
at the same hour in every month. 
The fourth process was the laying down these mean values on paper divided into 
square portions of 144 to one square inch, and considering that every division corre- 
sponded to twenty minutes of time ; the numbers being laid down as ordinates with 
“ the time of day” for abscissa. 
The fifth step was drawing a curve line passing through or near every point in 
every month at all the hours, giving equal weight to every point. In nearly every 
case a simple curved line passed through all the points. 
The sixth and last step was the measuring the ordinates at every Greenwich hour, 
and in this way the tables were formed. 
The accordance in the results at the same hour in the same month in the different 
years being found so close and satisfactory, together with the fact of a simple curve 
passing through all the points, the diurnal march, as shown in the Tables, may be 
considered as a very close approximation to the facts of nature. 
There is a promise at present of systematic observations being taken at many 
places in England, and by gentlemen of assured competency; these tables will assist 
such persons very much in determining at what times observations should be taken 
to determine different atmospherical elements. 
As a remark applying to all the Tables in this paper, I may here mention that ob- 
servers will find that comparatively a very few observations in each day, at hours by 
no means inconvenient in ordinary life, will furnish a near approximation to the 
mean and extreme values, as well as to the diurnal and annual variations of atmo- 
spherical phenomena. 
