ON ANEMOMETRY. 345 
4 Table of Mean and Minimum and Maximum Wind-pressures during 96 
hours. 
. Maximum.| Minimum. Mean. 
First twelve hours ...........+ 25 0°5 1°5 lb. 
Second twelve hours ......... 2:0 1:0 1:5416+ 
Third twelve hours ........- 3°5 20 2°5 
Fourth twelve hours ......... 4°5 3:0 3°5416-+- 
Fifth twelve hours........... | 45 25 3°29164 
Sixth twelve hours ......... 25 2:0 2°125 
Seventh twelve hours ...... 2:0 1:0 1:54 
Eighth twelve hours ......... 2:0 05 1:0 
The regularity of the results is conspicuous when represented by curves. 
_ The central ordinate of pressure is seen to occur two hours before the middle 
hour of time. It occurs in a lull of the wind. 
It is much to be wished that the numerous observations which have been 
made with Osler’s anemometer under the direction of the Association, should 
_ be reduced and tabulated so as to determine from them the annual air-move- 
_ ments over the place of observation, for comparison with the result given by 
Mr. Harris at Plymouth. The registers for Inverness, Edinburgh, Dublin, Bir- 
- mingham, Greenwich and Plymouth, thus brought together, would afford a valu- 
able basis for reasoning on the leading vicissitudes of British climate. This will 
probably be included in the reductions on which Mr. Harris is now engaged. 
It is neither an obvious nor an easy thing to obtain correctly the mean 
velocity of air-movement, or the total horizontal transference of the air in a 
given period, from the register of wind-pressure. The momentary velocity 
‘is a constant function (the square root) of the momentary pressure ; but the 
‘mean velocity is not a constant function of the mean pressure; the total air- 
“movement is not a constant function of the sum of the pressures. The larger 
the range of these pressures, the more variable is the relation of the mean 
velocity and the mean pressure ; the duration of the several values of pres- 
‘sure influences the calculation of the total air-movement, so that to obtain it 
even approximately from a register of momentary pressures a great number 
of these must be separately valued and reduced to velocity, and this is a great 
arithmetical labour. It might be diminished if we could assume as sufficiently 
known, the Jaw of the variation of the pressure, from 0 to the maximum, and 
calculate corrections in conformity with the successive swellings and sub- 
sidings of the wind; but this would still leave the result unsatisfactory. 
ressure in ~ Velocity in 
8. per foot miles per 
iquare. hour. 
meee > ~~~ ~~ ~~~ ~~ ~~ | - - - - - - - ~~ +--+ ~~ ~~~ ~~ - + --)  - --  i} - - - - o -  - 
Mee 
ETE: 
| nt 
Il ili y a Mu a 
- aaa WE SES 
_ A mechanical process may be substituted with evident advantage. If on 
1846. P = 
$ lhour } 
BSE) 
