METEOROLOGY. 



543 



the water parting between the Firths of Forth 

 and Clyde, furnish striking effects. The val- 

 leys of the counties of Kirkcudbright with 

 Dumfries and the intervening ridges lie athwart 

 the course of the rain-bearing winds, and show 

 the inevitable result of a rainfall successively 

 diminishing on advancing eastward. Several 

 local characteristics of rainfall, fully described 

 in Mr. Buchan's paper, afford some remarkable 

 illustrations of the principles by which the 

 amount of precipitation is controlled or modi- 

 fied. In Scotland, no rain-gauge gives an an- 

 nual average under 25 inches ; but the driest 

 regions, where that figure is only a little ex- 

 ceeded, are those which are protected by high- 

 lands from the rains of the southwesterly winds, 

 and also from the down-pours of the south- 

 easterly winds. In Ireland, only a small dis- 

 trict round Dublin shows a rainfall of less than 

 30 inches, and this district is protected by the 

 Wicklow mountains. As in that island there 

 is no continuous mountain-mass stretching 

 north and south, there is no such great differ- 

 ence of rainfall and temperature between its 

 eastern and western climates, as in the case of 

 Scotland and England. The results of the in- 

 quiry, as a whole, show that the key to the 

 distribution of the rainfall of the islands is the 

 direction of the rain-bringing winds in their 

 relation to the configuration of the surface. 



Mr. Blanford has deduced from the study 

 of the meteorological registers the following 

 theory of the winter rains of northern In- 

 dia: We have, in the first instance, steady 

 evaporation over an extensive moderately 

 humid tract, at a comparatively low tem- 

 perature, but in an atmosphere, the still- 

 ness of which allows the steady diffusion of 

 the vapor to high levels, and the consequent 

 fprmation of cloud. The slight disturbance of 

 the baric equilibrium which follows is suc- 

 ceeded by a gentle indraught of warmer and 

 more humid air from the south; for the Hima- 

 laya bars access to northerly winds. A vortex 

 is then rapidly formed, accompanied with an 

 increased cloud-formation, and speedily fol- 

 lowed by precipitation, which takes the form 

 of snow on the hills and rain on the river- 

 plains. The rainfall is invariably succeeded 

 by a cool wind, and a wave of high pressure 

 from the west, which the author attributes to 

 a drainage of cool, heavy air from the valleys 

 of the hills surrounding the Punjaub and the 

 highlands of Beloochistan and Afghanistan 

 air cooled by precipitation on the mountains. 

 If this theory be correct, the stillness of the 

 atmosphere, combined with the presence of a 

 moderate evaporation, must be accepted as the 

 condition which primarily determines the for- 

 mation of barometric minima and the winter 

 rains of northern India. 



Dr. Hellmann, in communicating the tabu- 

 lated results of the registration at eleven sta- 

 tions west of Berlin, for the six months from 

 July to December, has called attention to the 

 fact that in the winter months the values yield- 



ed by the different rain-gauges coincided very 

 closely, whereas in summer differences reach- 

 ing as much as 50 per cent, occur. 



Kain fall -maps of the Cape Colony were 

 shown at the Indian and Colonial Exhibition 

 in London, in which were embodied the re- 

 sults of observations made at 75 stations, which 

 had been in operation for five years previous to 

 the end of 1883, and at other stations where 

 observations had been taken for less time. 

 They show that the conditions which determine 

 the rainfall are not the same for the whole of 

 South Africa. In the southwest district of the 

 Western Province the most rain falls in the 

 winter months, while in the Eastern Province 

 and in Natal and the Orange Free State the 

 greater portion falls in the summer. On the 

 southern seaboard of the Cape Colony the rain- 

 fall is irregularly distributed throughout the 

 year. The northwest part of the colony ap- 

 pears to be almost rainless. With the excep- 

 tion of the tract occupied by the Namaqualand 

 mountains, the average yearly fall in this des- 

 ert is less than 6 inches. Throughout most 

 of the colony the yearly rainfall varies 

 from 6 to 18 inches." The smaller falls are 

 characteristic of the regions in the interior, 

 generally known as "the Karroo," including 

 plateaus from 2,000 to 4,000 feet above the 

 level of the sea; while the greater falls are 

 found nearer the sea and in the mountainous 

 parts. According to Mr. Gamble, the hy- 

 draulic engineer of the colony, the variations 

 in the rainfall are due chiefly to the sea-cur- 

 rents and the prevailing winds. The eastern 

 regions get their rains chiefly in summer with 

 the southeast trade- wind; the western mainly 

 in winter, with the northwest wind. From 

 whatever direction the rain may come, it sel- 

 dom penetrates beyond the mountain-range 

 which runs parallel to the coast. 



Storms. From a study of 650 thunder-storms 

 that occurred in Italy in 1881, Signor Ferrari 

 concludes that every thunder-storm is con- 

 nected with a barometric, hygrometric, and 

 thermic depression, being behind the two for- 

 mer and in front of the last. All three depres- 

 sions, but especially the two latter, are associ- 

 ated with maxima, which are situated behind 

 the barometric and hygrometric depressions, 

 but before the thermic one. For a given mo- 

 ment the thunder-storm has the form of along, 

 narrow band, advancing, with numerous bends, 

 outward and inward, parallel to itself, and 

 having its various characteristic phenomena 

 most intense along the middle line. The 

 isohyetes, or curves of equal rainfall, often 

 take the form of ellipses, whose longer axes 

 coincide with the direction of the storrn. The 

 dominant wind-direction is generally parallel 

 to that of the propagation af the storm. 



Although actual observations of the birth of 

 a storm are lacking, Mr. W. Clement Ley, in 

 reviewing the storms of October and early No- 

 vember in Great Britain, premises the follow- 

 ing as the conditions which would probably be 



