NATURE 



^}>i 



THURSDAY, JANUARY 13, 1881 



BAROMETRIC CYCLES 



ABOUT twelve years ago Mr. Baxendell of Man- 

 chester gave evidence of a connection between the 

 convection-currents of the earth and the state of the sun's 

 surface, and the subject has since been much discussed 

 by meteorologists from various points of view. 



Amongst these Mr. Meldrum of the Mauritius Obser- 

 vatory has brought forward much evidence in favour of a 

 connection between sun-spots on the one hand and rainfall 

 and cyclones on the otlier. Still more recently the Indian 

 meteorologists, including the names of Messrs. .Archibald, 

 Blanford, Broun, Charles and Frederick Chambers, 

 Eliot, and Hill have studied with much success the 

 abnormal variations of barometric pressure in the tropics. 

 Of these the researches of Mr. F. Chambers are parti- 

 cularly interesting ' as exhibiting a very close relation 

 between such barometric fluctuations and the state of the 

 sun's surface. 



The chief principle underlying these investigations is 

 sufficiently obvious. We know that the marled differ- 

 ences in barometric pressure which exist between various 

 portions of the earth's surface must be due to the sun ; if 

 therefore ihe sun be in reality variable we should natur- 

 ally expect these differences to vary likewise in such a 

 way as to be strengthened when the sun is most powerful 

 and weakened when he has least influence. In accord- 

 ance with this way of regarding things, Mr. Chambers in 

 1S76 pointed out that the abnormal variations of the 

 monthly mean barometric pressure at Bombay in that 

 year were mainly variations in the intensity of the usual 

 seasonal movements, while in 1877 he attributed the uni- 

 formly high barometric pressure and the deficient rainfall 

 of that 5 ear to a weak development of the equatorial belt 

 of minimum pressure, probably induced by a diminution 

 of the solar heat. 



In a diagram attached to his first communication Mr. 

 Chambers compares the curve of solar-spotted area with 

 other curves denoting the barometric pressure at various 

 widely-distributed tropical stations, from which we can 

 clearly see that there is a very marked resemblance 

 between the salient points of the various curves on the 

 hypothesis that a large amount of sun-spots corresponds 

 to a low barometer. But besides this it appears that the 

 epochs of maximum and minimum barometric pressure 

 lag considerably behind the corresponding epochs of 

 minimum and maximum solar-spotted area, and that this 

 lagging behind is greater for easterly than for westerly 

 stations, or in other words the abnormal barometric varia- 

 tions in the tropics may be said to travel at a very slow 

 rate round the earth from west to east. 



Perhaps the subject of greatest practical importance in 

 these communications is the discussion regarding Indian 

 famines and their connection with sun-spot minima — a 

 connection first brought to light by Dr. Hunter. Mr. 

 Chambers sums up his conclusions on this point as 

 follows : — 



I. Variations of the solar-spotted area are succeeded 

 months afterwards by corresponding abnormal barometric 



* See Nature, November 25 and December 2, 1880. 



Vol. xxm. — No. 585 



variations, a high barometer corresponding to a minimum 

 of sun-spots. 



2. Famines follow in the wake of curves of high baro- 

 metric pressure. 



Finally two methods are indicated by which early 

 intimation of the approach of those meteorological dis- 

 turbances which are attended by famines may possibly 

 be obtained. 



1. By regular observation of the solar-spotted area, and 

 early reduction of the observations, so as to obtain early 

 information of current changes going on in the sun. 



2. By barometric observations at stations differing 

 ■widely in longitude and the early communication of the 

 results of stations situated to the westward. 



While it thus appears that the evidence in favour of a 

 connection between the state of the sun's surface and the 

 meteorology of the earth is continually acccumulating it 

 may not be amiss to review briefly the present position of 

 the problem. 



In the first place Mr. Meldrum, as already mentioned, 

 has given evidence that in numerous stations the rainfall 

 is greater about times of maximum than about times of 

 minimum sun-spot frequency. 



Secondly. Through his labours apd those of M. Poey 

 we have reason to believe that there are more cyclones in 

 the Indian Ocean and hurricanes near the West Indies 

 during times of maximum than during times of minimum 

 sun-spot frequency. 



Thirdly. There is the connection between the baro- 

 metric fluctuations of the tropics and the state of the 

 sun's surface which has just been pointed out. 



Fourthly. From investigations in which I have been 

 recently engaged there is reason to suppose that sun-spot 

 inequalities of short duration are followed by corre- 

 sponding inequalities in the diurnal temperature range of 

 Toronto in such a way that a large amount of sun-spots 

 slightly precedes a large temperature range. 



Fifthly. To go from meteorology to magnetism there is 

 the well known connection first observed by Sabine, in 

 virtue of which the diurnal oscillations of the magnet are 

 greatest about times of maximum sun-spots. And I may 

 add that magnetic maxima lag behind sun-spot maxima, 

 while there are also indications that magnetic weather, 

 like meteorological weather, travels from west to east. 



We thus perceive how strong the evidence is in favour 

 of some connection betw-een the state of the sun's surface 

 and terrestrial meteorology, while at the same time it is 

 unmistakably indicated by all elements that this connec- 

 tion is of such a nature as to imply that the sun is most 

 powerful v\hen there are most spots on his surface. Add 

 to this that the spectroscopic observations of Lockyer 

 and others tend in the saine direction, as well as such 

 actinometric results as we have been able to procure, chiefly 

 through the labours of Mr. J. H. Hennessey at Dehra 

 Dhoon and Mussoorie. 



In fine this hypothesis is rapidly emerging, if indeed it 

 has not already emerged, from the regions of mere 

 conjecture. 



But here it is necessary to bear in mind the following 

 considerations. Prof. Stokes has pointed out that the 

 problem before us really involves two questions, which 

 may be stated as follows : — Firstly, do the changes which 

 take place in the sun's surface correspond to changes in 



