466 



Sir N. Lockyer and Dr. W. J. S. Lockyer. [Apr. 13, 



mention may be made of the very great area which was covered by the 

 continuous excessive high pressure that prevailed over the Indian 

 region from the end of 1876 to about the middle of 1878. 



On fig. 1 is given a map of the world on which are marked the 

 types of pressure variations in each region which is included in this 

 barometric survey. 



An attempt has been made by means of a neutral line to show 

 approximately the mean lines of separation of these two chief 

 pressure types, although it must be remembered that this line is liable 

 to a probable small oscillation about its mean position. 



As far as can at present be determined, one line commencing to the 

 west of Alaska, separating this region from Siberia, passes easterly 

 along about the 60° parallel of latitude and runs in a south-easterly 

 direction between South-west Greenland and North-east Canada. It 

 then crosses the North Atlantic, passing to the north of the Azores, and 

 skirts the south-western portion of Portugal. It then strikes down 

 towards the Equator, cutting North-west Africa, as far as can be 

 judged from the scant pressure values available, through the middle of 

 the Sahara. It leaves Africa near the Gold Coast, passes into the 

 South Atlantic, where it cannot be traced further owing to lack of 

 observations in this southern ocean. 



The other boundary or neutral line passes to the north-east of 

 Greenland and north of Iceland, crosses the southern portion of 

 Norway and Sweden, and traverses Southern European Russia. It 

 then takes a course somewhat more easterly, skirting the northern part 

 of the Caspian Sea and Turkestan, passes between Tibet and Mongolia, 

 and through China. It then leaves the Continent a little to the south 

 of the Yellow Sea, and passes into the North Pacific Ocean. Here its 

 path cannot be traced, but it evidently passes well to the east of the 

 Philippine Islands, and Solomon Islands, takes a new south-westerly 

 course, skirting the eastern side of Australia and passing between 

 Tasmania and New Zealand. Its track is then again lost in the; 

 Southern Pacific Ocean. 



Although too much weight must not at present be given to the 

 positions of these neutral lines throughout their whole length, it is 

 interesting to note that they are fairly symmetrical to one another 

 although no attempt has been made to make them so. 



Both lines apparently cross the equator at about antipodal points, and 

 both appear to have a similar trend in northern and southern latitudes. 



We seem then to be in presence of a general law relating to the- 

 pressures which occur simultaneously in two different regions of the 

 globe, separated and defined more or less by a neutral line, this neutral 

 line forming a fulcrum about which see-saws of pressure from on& 

 region to another take place. Special cases of such reverse pressure 

 variations have been previously detected. 



