CLIMATES OF GREAT MALVERN AND LONDON. 2*21 



The hygrometer, when consulted with a view of predicting the 

 greater or less probability of rain, or other atmospheric changes — 

 two things are principally to be attended to, the diflFerence between 

 the temperature of the dew-point, and the temperature of the air, and 

 the variations that may occur between them. In general the 

 chance of rain, or other precipitation of moisture from the atmos- 

 phere, may be regarded as in inverse proportion to the difference 

 between the two thermometers, one marking the dew-point, the 

 other the temperature of the air. An increasing difference, accom- 

 panied with a fall in the former, is an almost sure prognostic of 

 fine weather j whilst a diminution in the temperature of the air, 

 and a rising dew-point, portend rain. In winter, when the differ- 

 ences between the dew-point and the temperature of the air are 

 always small, the indications must be taken more from the actual 

 rise and fall of the dew-point, than from the difference between it 

 and the temperature of the air. A sudden change in the dew- 

 point is generally accompanied by a change of wind, and the 

 former sometimes precedes the latter by a short interval j and the 

 course of the aerial current may then be anticipated before it affects 

 the direction of the weathercock, or even the passage of smoke. A 

 rise in the dew-point, accompanied with a fall of the barometer, is 

 an infallible indication that the whole mass of the atmosphere 

 is becoming imbued with vapour, and a copious precipitation may 

 be expected. If a fall in the barometer, and a fall in the tempera- 

 ture of the dew-point, take place at the same time, we may conclude 

 that the expansion which occasions the former has arisen at some 

 distant place, and wind, not rain, will be the result.* 



WIND. 



In comparing the direction of the wind at Malvern with that in 

 London, we have adopted a very easy, but not perhaps the most 

 desirable classification. The hills at the former place influence so 

 much their force and direction, that it is often very difficult to 

 determine precisely the point whence the great atmospheric cur- 

 rent comes ; it is not always that there are clouds by which to 

 determine, besides, when these are high, it not unfrequently hap- 

 pens that they are subjected to the movements of the higher cur- 

 rents, and passing away in a direction quite opposite to the wind 

 below. On these accounts we shall denominate all those winds 

 blowing from the south of east and west, vapour winds, and those 

 blowing from the north of these points, dry winds, — 



June. July. August. 



1834. Vapour. Dry. Vapour. Dry. Vapour. Dry. 



London 23 .... 7 15 .... 16 19 .... 12 



Malvern 23 .... 7 16 .... 15 17 .... 14 



TOTAL FOR THE SUMMER. 



Vapour. Dry. 



London 57 35 



Malvern 56 36 



* Vide Daniell's Meteorological Essays. 



