Dr. Edw. Jaderin — On Variations of Climate. 435 



alteration in course of time. A long series of records relating to the 

 date of the grape-harvest reaching back to the year 1400, as well as 

 measurements of the level of the water in lakes and rivers up to the 

 year 1700, enable us to fix the average duration of each of the 

 periods in question at 36 years. 



The law of the weather theory in general has for a long time 

 been familiar to a large portion of the public. The diurnal synoptic 

 charts show an attentive examiner the connection between the 

 height of the barometer, the direction of the wind, temperature, and 

 rainfall, whilst the charts drawn up for the purpose of showing the 

 annual means of the barometer, etc. — i.e. the climatic charts — explain 

 the same relation between the meteorological factors. We find, for 

 instance, on one of them somewhere in the Northern Hemisphere 

 an area with an average low pressure, and we shall then also find 

 how the wind, just as on the synoptic charts, which show the state 

 of the weather on a certain occasion, rotates around this area sun- 

 wards with a movement towards the centre of the spiral. From this 

 it results that the change noticed in the rainfall must depend upon 

 analogous changes in the direction of the wind and the atmospheric 

 pressure. In a scientific work upon this pressure, based upon 

 observations carried on during many years in Europe and Northern 

 Asia, it is shown that such periodical variations also occur in the 

 barometric pressure. 



From observations recorded since 1826 within the Temperate 

 Zone of the Old World, it appears that each rain period, viz. 

 1841-55, and 1866-85, is followed by a reduction of all differences 

 in the barometric pressure, and that each dry period, viz. 1826-40 and 

 1856-65, is followed by an increase of differences in the barometric 

 pressure. Both when speaking of the division of the atmospheric 

 pressure over different areas of the earth's surface and in respect of 

 this division during different seasons in a certain place, the expression 

 " difference in the atmospheric pressure " is suitable, and a reduction 

 of the differences in the barometric pressure during a certain period 

 indicates a more even division of the pressure than usual over the 

 earth's surface, as well as a smaller variation than the normal during 

 the year. 



The change in the barometric pressure explains not only the 

 variation in the rainfall occurring according to the natural law, but 

 also the existence of areas with differing conditions. 



Just as on one side the rainfall is dependent upon the variability 

 of the barometric pressure, the latter in turn must exercise influence 

 upon the amount of heat received by the earth, and an increase of 

 the latter during a dry period accentuates the contrast between 

 land and sea. 



It would be of additional value to deal with the variations of the 

 climate indicated by Bruckner as regards their equal duration and 

 internal relation. They have not only a purely scientific, but a 

 practical importance, as they exercise influence upon changes in the 

 level of lakes and rivers, and thus in many localities the time of then- 

 freezing too, and therefore indirectly upon navigation and trade. 



