256 DISCUSSION OF THE DESICCATION QUESTION. 



quences. In the region in question, orographic causes seem to have been 

 combined with climatic ones in just the way most likely to result in bringing 

 about the rapid desiccation of an extensive region enclosed within the largest 

 land mass of the globe. A very small elevation of the flat regions of North- 

 ern Europe and Asia was sufficient to raise an extensive area above the sea- 

 level, and thus to give rise to conditions powerfully affecting the climate of a 

 correspondingly large portion of the adjacent countries. 



The causes of the fluctuations of climate, or of the variations in the mean 

 temperature from year to year, are quite obscure. We know, as a fact, that 

 after a few years during which the temperature has been higher than the 

 mean of a long series of years, there will be a succession of colder ones, and 

 that occasionally there will be one or more years remarkable for their ab- 

 normal character. The same is true in regard to rain-fall. What causes 

 these successions of periods of warmer and cooler, or of moister and drier, 

 years is as yet a mystery. All attempts to discover the law of their re- 

 currence or to find any regularity about them have failed. It has been 

 a favorite theory with many that these fluctuations might be in some way 

 coimected with the sun-spot cycle ; but no one has been able to prove that 

 this is the case. It is now pretty certain that the influence of the sun-spots 

 on climate must be exceedingly small, — by far too small to admit of its 

 being taken into account as a matter of practical imj^ortance.* 



The fluctuations of the weather from year to year are precisely in the 

 same category as the inception of those disturbances of the atmospheric 

 conditions called storms. Of the manner in which storms move after they 

 have been once started, and of the character of the phenomena by which 



* Plantanioiir, in his elaborate discussion of the climate of Geneva, to which reference has already heen made, 

 shows that there was a warm cycle between 1826 and 1834, during which time there were seven abnormally warm 

 years and only two cold ones. This was followed by a cold cycle ; between 1835 and 1860 there were twenty-two 

 cold and only four warm years ; again a warm cycle occurred, and between 1861 and 1875 there were thirteen warm 

 years and only two cold ones. The inference drawn from these facts is thus stated by Plantamonr : " There is 

 therefore a very marked predominance of warm years during one epoch, and of cold ones in another ; from which 

 it may be concluded that accidental conditions tending to modify the temperature one way or the other, exercise 

 an iuHuence in the same direction, not however in any continuous manner, but with a distinct preponderance 

 during several consecutive years." In regard to the question of a periodical recurrence of abnormally warm and 

 cold years, the following remarks are made by the same author : " It is certainly not possible to discover the least 

 trace of periodicity in the return of these maxima and minima, the mean of which coincides almost exactly with 

 the general mean." The mean temperature of live of the warmest years was found to be 10°.52 (Cent.) ; that of 

 five of the coldest ones 8°.25; mean of these luinibers t!°.3S; mean of all the observations from 1826 to 1875, 

 9°. 347. A similar absence of any proofs of regular periodical recurrence of years of greater or less rain-fall is also 

 given by Plantamour as tlie result of the most careful working over of the observations of fifty years. 



