620 



SCIENCE. 



[N. S. Vol. XVIII. No. 463. 



found to lag very persistently about one 

 month behind the Bombay curve. 



Similar results Avere then worked out for 

 other stations. St. Helena, Mauritius, 

 Madras, Calcutta and Zi-ka-wei. On com- 

 paring the curves obtained for these vari- 

 ous places, though a strong resemblance 

 in form betwen all the curves is observed, 

 there is also strong evidence of a want of 

 simultaneity in the barometric movements 

 at different stations, and that as a rule 

 the changes take place at the more westerly 

 stations several months earlier than at the 

 more easterly ones. 



Thus, on comparing the curves for St. 

 Helena and Madras from 1841-1846, the 

 latter sometimes lagged behind the former 

 as much as six months, and for Bombay 

 and Calcutta the corresponding difference 

 was often upwards of six months. 



The facts suggested to him long atmos- 

 pheric waves (if such they may be called) 

 traveling at a very slow and variable rate 

 round the earth, from west to east, like 

 the cyclones of the extra-tropical latitudes. 



With special reference to famines, he 

 remarked that, on comparing the dates of 

 all the severe famines which have occurred 

 in India since 1841, widespread and severe 

 famines are generally accompanied or im- 

 mediately preceded by waves of high baro- 

 metric pressure. He suggested, therefore, 

 that intimation of the approach of famines 

 might be obtained in two ways : 



(a) By regular observations of the solar 

 spotted area, and early reductions of the observa- 

 tions, so as to obtain early information of cur- 

 rent changes going on in the sun. 



(6) By barometric observations at stations 

 differing widely in longitude, and the early com- 

 munications of the results to stations situated to 

 the eastward. 



In the same year. Dr. H. F. Blandford 

 discovered that* : 



Between Russia and Western Siberia on the one 

 hand, and the Indo-Malayan region on the other, 



* Nature, Vol. XXL, p. 480. 



there is a reciprocating and cyclical oscillation 

 of barometric pressure, of such a character that 

 the pressure is at a maximum in Western Siberia 

 and Russia about the epoch of maximum sun- 

 spots, and in the Indo-Malayan area at that of 

 minimum sun-spots. 



Up to 1881, the general idea had been 

 that there was a great dift'erence between 

 the meteorological conditions at the maxi- 

 mum and minimum of the sun-spot curve, 

 but the more numerous and more accurate 

 series of observations available in the year 

 in question revealed to Meldrum 'extreme 

 oscillations of weather changes in different 

 places at the turning points of the curves 

 representing the increase and decrease of 

 solar activity.' 



This was a most important change of 

 front. Not the maximum only, but both 

 the maximum and minimum had to be con- 

 sidered.* 



In relation to these pressure changes he 

 wrote as follows :f 



Among the best established variations in ter- 

 restrial meteorology which conform to the sun- 

 spot cycle, are those of tropical cyclones, and the 

 general rainfall of the globe, both of which imply 

 a corresponding variation in evaporation and the 

 condensation of vapor. Now the variation of 

 pressure with which we have to deal evidently 

 has its seat in the higher (probably the cloud- 

 forming) strata of the atmosphere. This is not 

 only illustrated in the present instance by the 

 observed relative excess of pressure at the hill 

 stations as compared with the plains, but also 

 follows as a general law from the fact established 

 by Gautier and Koppen, viz., that the temperature 

 of the lowest stratum varies in a manner antagon- 

 istic to the observed variation of pressure. It is 

 then a reasonable inference that the principal 

 agency in producing the observed reduction of 

 pressure at the epoch of sun-spot maximum is 

 the more copious production and ascent of vapor, 

 which may operate in three different ways. First, 

 by displacing air the density of which is three 

 eighths greater; second, by evolving latent heat in 

 its condensation; and thirdly, by causing ascend- 



* ' Relations of Weather and Mortality, and in 

 the Climatic Effect of Forests.' 

 t Nature, XXI., p. 482. 



