NA TURE 



525 



THURSDAY, OCTOBER 2, 1879 



THE GREENWICH METEOROLOGICAL 

 OBSERVATIONS 



Reduction of Greenwich Meteorological Observations. 

 Barometer, 1854-1873; Air and Moisture Thermome- 

 ters, 1849-1868; and Earth Thermometers, 1847-1873. 

 Made at the Royal Observatory, under the Direction of 

 Sir George Biddell Airy, K.C.B., Astronomer-Royal. 

 (London, 1878.) 



AN important contribution has recently been made to 

 the meteorology of England by the Astronomer- 

 Royal in the issue of this volume, which contains elaborate 

 discussions of the photographic records of the barometer 

 from 1854 to 1873, of the photographic records of the dr)'- 

 bulb and wet-bulb thermometers from 1849 to 1868, and 

 of the eye-observations of the thermometers whose bulbs 

 are sunk to different depths in the ground from 1847 to 

 1873. The photographic apparatus and the details of the 

 instruments and their mounting are fully described, and 

 the methods for the reduction of the photographs to num- 

 bers, and the discussion of the results, are explained at 

 length. 



There can be no doubt that in these twenty years' 

 averages wc have the closest approximation to the mean 

 monthly diurnal inequality of the barometer, in other 

 words, to one of the prime factors of the meteorology of 

 Greenwich. Of special interest are the results for the 

 warmer months of the year, which class Greenwich among 

 the places in middle and higher latitudes, whose climates 

 are more or less continental in their character — these 

 more special features being the occurrence of the fore- 

 noon maximum as early as 9 A.M., and a marked diminu- 

 tion in the amount and amplitude of the morning 

 minimum. The almost strictly local character of the 

 diurnal phases of atmospheric pressure, as disclosed by 

 the observations at Greenwich, is seen from the occur- 

 rence of the A.M. maximum an hour earlier at Kew, where 

 also the A..M. minimum becomes still less pronounced 

 than that of Greenwich. On the other hand, at 

 Falmouth, the a.m. minimum is much the greater of 

 the two daily minima, and the A.M. maximum is delayed 

 from two to three hours later than at Greenwich. Hence 

 the true value of the Greenwich results can only be 

 appreciated after a comparison has been made between 

 them and the results obtained from other meteorological 

 observatories. 



An extremely interesting discussion has been carried 

 out, showing the relations between the diurnal inequality 

 of pressure and the different directions of the wind for 

 the months. The results, while showing the double 

 maxima and minima, show also in every case that the 

 diurnal ciu-ve is thrown up or down, sometimes very con- 

 siderably so. The reason for this uptilting of the curves 

 or the reverse, is readily seen if we refer the phenomena 

 to the European storms which affect the winds and 

 pressure at Greenwich in their eastward course. Thus 

 E., S.E., S., and S.W. winds, being in the front segment 

 of storms, are accompanied with a falling barometer, and 

 consequently the curves of diurnal inequality of pressure 

 for each of these winds appear thrown down, most so in 

 Vol. XX.— No. 518 



case of S.E. winds ; whereas W., N.W., and N. winds 

 which prevail in the rear of storms and are attended with 

 a rising barometer, present curves which are thrown up, 

 the uptilting with N.W. winds being remarkably great. 

 These effects are most decided during the stormiest half 

 of the year. 



The observations of temperature are discussed with 

 particular fulness, and the length of time is sufficient to 

 give curves showing a diurnal inequality of temperature 

 such as will substantially represent the curves for large 

 portions of the south of England, not bordering the 

 sea, where the thermometers are similarly placed to those 

 at Greenwich, 



The curves of temperature for the different winds have 

 also been worked out with much elaboration, and give 

 most interesting results. We would refer specially to the 

 diagram on page 18, showing the air-temperature curve 

 for December, with the diurnal curve for the same month, 

 when the N.W. wind blew, from which it is seen that 

 while the curve for N.W. winds has substantially the 

 same form as the general curve for the month, it superadds 

 a gradual fall of about 4°o during the twenty-four hours. 

 On comparing the temperature of the air at midnight with 

 that at the following midnight, it is shown that a clear 

 sky lowers the temperature considerably in November, 

 December, and January, but raises it in other months, 

 particularly in May, June, and July ; whereas an overcast 

 sky scarcely disturbs the temperature, so that on an 

 average it stands at the same point at the end as at the 

 beginning of the twenty-four hours. On the average of 

 all months the N. wind is the coldest, the S.W. the 

 warmest ; the order as regards temperature, beginning 

 with the coldest, is N., N.E., N.W., E., S.E., W., S., 

 S.W. — an order, however, which differs in different 

 months. The results of changes of wind differ greatly 

 with season ; thus a change of wind from N.E. to S.W. 

 raises the temperature li°'o in January, but only o°"3 in 

 June. 



The earth thermometers were made under the super- 

 intendence of the late Prof. J. D. Forbes, and placed in 

 position in 1846, the graduation of these thermometers 

 having been made by Prof. Forbes himself. The hour of 

 observation has been noon, but during 1846-47 observa- 

 tions were made every two hours, from the results of 

 which " corrections ' ' have been obtained for the reduc- 

 tion to approximate mean temperatures. The following 

 are among the more important results : — 



Mean coldest\ 

 month . . 



Mtran warmest! 

 month . . ./ 



Difference . . 



Mean annual 

 temperature, 



Earth thermometers at depth of 



1 inch. 



Jan. 4o*'38 



July 64' 34 

 23 -96 



51 ■«4 



3'a feet. 



Mar. 43''48 



Aug. 6i°'38 

 1890 

 5"">3 



6'4 feet. 



Mar. 44'-79 



Aug. 59"-«o 

 I4'8l 

 5l'53 



la-Sfeet. 



Apr. 46°'42 

 Sept 55'74 



5087 



aS'S feet. 



June 48"-94 



Nov. 53''ai 



3'a» 



So'SS 



The mean temperature of the air from observations 

 made with a thermometer in the perforated wooden box 

 protecting the projecting scales of the thermometers is 

 5 1 "•59. But with the view of giving a more exact com- 

 parison between the temperature of the air and that of 



A A 



