METEOROLOGICAL RESULTS

DEDUCED FROM OBSERVATIONS TAKEN AT THE
LIVERPOOL OBSERVATORY

DURING THE FIVE YEARS ENDING DECEMBER 31ST, 1850.

BY

JOHN HARTNUP, ESQ., F.R.A.S.

(READ BEFORE THE SOCIETY IN THE SESSION 1850-51.)

Latitude of the Observatory, 53° 24' 48" N.; Longitude, 3° 0' 1" W. Cistern of the Barometer elevated 37 feet above the mean level of the Sea.

THE Meteorological observations which have been taken at the Liverpool Observatory now extend over a period of five complete years, and the whole of these observations have been reduced on one uniform plan. The mean and extreme values have been deduced with great care, and the monthly and yearly changes which have taken place in our atmosphere, during the above named period, have I believe been traced with very great accuracy in the accompanying tables.

The instruments with which the observations have been taken were all made by Mr. Adie, of Bold-street, Liverpool. They consist of a STANDARD BAROMETER of Neuman's construction, the tube of which is nearly an inch in diameter; a MAXIMUM THERMOMETER, and a MINIMUM THERMOMETER Of Rutherford's construction; a RAIN GUAGE of Howard's con struction; and A PAIR OF WET- AND DRY-BULB THERMOMETERS having a scale of about one tenth of an inch to a degree.

During the whole time over which the observations extend, the instruments have occupied the same situation. Up to the end of June, 1849, they were all read daily at two hours, Göttingen mean time, which corresponds with one hour twenty minutes Greenwich mean time. Since the end of June, 1849, they have all been read daily at 1 P.M., Greenwich mean time. This difference of twenty minutes in the times of reading has been taken into account in the application of the corrections to the instrumental readings for diurnal range.

The index correction which has been applied to all the readings of the barometer, to make it read the same as the Royal Society's flint-glass standard, was obtained by the transmission of a portable barometer of Troughton's between the Greenwich and Liverpool Observatories. The index correction which has been applied to each of the thermometers, was obtained by comparison with a pair of thermometers, which had been previously compared with the standard thermometer at the Royal Observatory. The index correction was found to be so near the same in different parts of the scale of each of the thermometers, that no alteration has been made for error of scale.

The corrections for diurnal range have been derived in the following manner. During the five years ending December, 1845, meteorological observations were taken at the Royal Observatory at Greenwich at every even hour of Göttingen mean time. From these observations tables were formed by Mr. Glaisher, shewing the corrections to be applied to the monthly mean of the daily readings of each instrument at any hour, in order to deduce the true mean reading for the month from observations taken at that hour. These tables were published in the Transactions of the Royal Society, part 1, for 1848. For the Barometer the corrections for the different months in the year range from + 0·007 in. to- 0.006 in., for the hour at which these observations have been made, and

these corrections have been applied, as they are doubtless sufficiently accurate for all practical purposes.

For the Dry-Bulb Thermometer the table of corrections obtained from the Greenwich observations would not satisfy the observations made at Liverpool, but as this correction appeared to depend on the diurnal range of the thermometer, a table of factors was formed by dividing the corrections given in the table for each hour at Greenwich, by the diurnal range of the thermometer at Greenwich. These factors when multiplied by the diurnal range of the thermometer at Liverpool, give corrections which satisfy the Liverpool observations. We can prove the truth of this in the following manner:-The mean of the readings of the dry-bulb thermometer taken daily at one o'clock should, when corrected for diurnal range as above described, give the true mean temperature. Again, the mean daily readings of the maximum and minimum thermometers, after the application of a correction found from the Greenwich observations and given in the above-named tables, should also give the true mean temperature.

Now, for each of the five years over which our observations extend the mean temperature obtained by the last named method has been in excess of the former, but the difference has never exceeded 0.4°, and it has never been less than 0.1°. The correction for diurnal range found in this way may therefore be considered sensibly perfect, for the index corrections which have been applied to the thermometers, notwithstanding the care that has been taken to obtain them correctly, may possibly be in error sufficiently to cause a difference in the mean temperatures derived by the two methods, as large as that which has been found to exist.

The corrections for diurnal range which have been applied to the Wet-Bulb Thermometer have been found in the following manner :-In the tables before named (Transactions Royal Society, part 1, 1848), Table V. shews the mean depression of the temperature of evaporation below that of air at Green

wich, at each hour in the day for every month in the year. Now, I have assumed that the depression at one o'clock, given for Greenwich, bears the same proportion to the depression at one o'clock found from observation at Liverpool, that the mean depression given for Greenwich, does to the mean depression required for Liverpool. The following example will explain how the corrections for diurnal range have been deduced.

For instance,

FOR THE MONTH OF MAY, 1850,-

The mean reading of the dry-bulb thermometer was 55.8°; of the wet-bulb thermometer, 49.4°; and the mean daily range of temperature was 10.3°.

By Glaisher's Table IV.,-0.412 is the Factor for Oh. 48m. local time, and 0.412 × 10-3° — — 4.24° the correction for diurnal range for the dry-bulb thermometer.

From observation at Liverpool, 6.4° was the depression of the wet below the dry-bulb thermometer at Oh. 48m. local time. From Glaisher's Table V., 5.88° is the depression for the same local time at Greenwich, and 3.01° is the mean of the twenty-four hourly depressions at Greenwich, therefore the difference is 2.87° for Greenwich.

correction for the dry-bulb), diminished by 3.12, or 1·12°.

I have been particular in describing how the mean temperature of the air from the dry-bulb thermometer, and the mean temperature of evaporation from the wet-bulb thermometer have been derived; because any error in these determinations must influence the whole of the hygrometrical deductions.

In the accompanying tables, column 1 contains the month and year to which the various results in the horizontal line opposite