1880.] 



in delation' to tlie Sun-spot Cycle. 



11 



Evidence bearing on the northern prolongation of the axis o£ maximum 

 pressm-e across Central Asia (at least up to the end of 1877) is afforded 

 by the old established observatories of the Russian empire ; the registers of 

 which, since 184!7, are given in the ' Annales de I'Observatoii-e Physique 

 Central de Russie'. Before, however, proceeding to notice the barometric 

 condition of this region during the special period in question, I must draw 

 attention to another class of facts, which have an important bearing on the 

 subject, and Avhich, although not entirely new, have been brought out in the 

 present investigation with remarkable clearness and prominence. 



I have already noticed the evidence furnished by the registers of 

 Singapore and Batavia, of a persistently low pressure from 1869 to the 

 latter part of 1873, of its gradual rise during the subsequent years, and its 

 culmination in 1877. The Batavian register extends as far back as 1866 ; 

 comprising, therefore, a period of 13 years, and sonaewhat more than a com- 

 j^lete cycle of sun-spot variation. The deviation of the mean pressure o£ 

 each year from the general average of the whole period is given in 

 the second column of Table II ; and, in the first, I have given the 

 variation of Wolf's sun-spots numbers up to 1875, the latest date for which 

 I have them. I need only add that from 1875 to the early part of the 

 l^resent year, was a prolonged period of minimum solar activity. The 

 coincidence of the barometric variation with that of the sun-spots is too 

 obvious to need comment ; and it is emphatically to be noticed that the 

 minimum of pressure coincides with the maximum of spots, and vice versa. 

 The remaining columns of the table give the annual deviation of the mean 

 pressure of each year from the general local averages, for the stations 

 Singapore, Port Blair, Colombo, Akyab, Chittagong, Calcutta, and Darjiling, 

 from 1867 to 1878 ; and the accompanying plate represents graphically the 

 course of variation at each station from year to year. All these exhibit, 

 more or less distinctly, an oscillation similar to that of Batavia ; being most 

 pronounced at insular and sub-equatorial stations. Table III gives the 

 annual barometric variation of Calcutta and Bombay from 1848 and 1852 

 respectively, and Plate I, the corresponding curves. 



