452 



KErORT — 1884. 



primarily only by Its radiation. This is the iileawliich forms the foumla- 

 tion of Professor JJalfour Stewart's work on the subject. Ho has also 

 thrown out the idea that connection currents in the outer parts of onr 

 atmosphere may, by their motion aci'oss the lines of magnetic force, indiicu 

 sensible currents. I do not believe that our present knowledge of tlio 

 passage of electricity through gases quite warrants tho assumption of 

 such a possibility, for though we may nuiko tho electric resistance in 

 some parts of the vacuum almost as small as we please, tho total 

 electro-motive forco which is capable ol' setting up a discharge at all must 

 always bo considerable. At any rate, it is absolutely necessary, befoiv.' 

 going further, to decide ■whether we can trace a connection betwe(;n the 

 number of sunspots and those terrestrial phenomena which depend on lii^ 

 temperature. It i.s only when wo are in possession of all the facts that 

 ■we may hope for a solution of tho mysteiy. 



lici 



i 



il 



(Jimnci'tltni of Sampol.'i mid Tempcrabur. 



We owe to Gautier ' the first detailed examination of this (juestioii, 

 which led him to the result that the y "■'ars of many sunspots arc probably 

 rather colder, those with few sunspots rather warmer, than tho averagf. 

 Other investigations led generally to a similar, occasionally, however, toii 

 contradictory result, until Koeppen, by means of a very exhaustive in- 

 vestigation, has given us some decisive results. Koeppen'^ has bmuglit 

 together the temperature records of nearly 2r)0 stations from diiforoii! 

 parts of the earth. 



These were divided into five groups, according to their geographical 

 position — namely, tropics, sub- tropics, the warmer parts of the tcmpcriilk 

 zone, the colder parts of the temperate zone, and the c!old zone. I'Jiicli of 

 these groups was examined separately. The curves are plotted down in 

 Plate II., and will show a very remarkable relationship to the suiispot 

 curve. The connectirn is most marked for tho tropics, then gradually ii> 

 ■we move away from the equator it becomes less and less distinct. The 

 following table, which compares together the years in which the maxima 

 and minima took place, will also render the connection very clear. Tlif 

 table in which the ectropical regions have been united is taken out nt' 

 Hahn's monograph. It is well known that sunspot periods differ in length, 

 and that the time between a maximum and a minimum is shorter than 

 that between a minimum and a maximum. This peculiarity is exactly 

 reproduced in the temperature curve, as tho comparison (Table II.) made 

 by Koeppen will show. The numbers express the years intervening 

 between two successive turning-points of the curve. 



The difference between the average temperature in a j'ear of maximum 

 and one of minimum sunspots is by no means small ; it reaches 0°73 C. 

 in the tropical regions, and u little over half a degree in the ectropical 

 groups. The maxima and minima of temperature in the tropics seem to 

 take place a little before the corresponding phases of the sunspot curve, 

 while tho ectropical regions show a retardation of the phase. The cum 

 shows some irregularities about the year 1860, but especially towards the 

 beginning of the century it is very much disturbed ; and, worse stil', 

 between 1780 and 1790 the effect seems exactly reversed. This lattei' 



« Ann. Chim. Phjs., III., XII. (1844). 



' Zeittchrlft der oeat. Ges. Met., vol. viii. pp. 241 and 257. 



