PART in. THE CYCLE OF A YEAR. 23 



would be produced there; in Lisbon four times as 

 much ; and in Jerusalem no less than seven times as 

 much. 



That, however, is for the average of the whole year ; 

 but if we next take account of the variations through the 

 monthly means of the year, we find these so small in 

 Scotland (or o'6 of a unit grain) that even in summer- 

 time the air can never have any very drying qualities. 

 Nor indeed can it have in Madeira, where the seasonal 

 variation amounts only to 1*3 grains on a large constant 

 supply ; but in Lisbon, where the variation mounts up 

 to 3*1 grains, the dry ness in summer-time must be 

 remarkable, and in Jerusalem, where it reaches 5*0 grains, 

 the summer droughts must be terrific. 



This quality of the air at the surface of the ground is 

 further illustrated by what takes place visibly aloft in the 

 vapour planes where clouds are usually formed. Thus 

 poor Scotland, with her low temperature, and close 

 approach therein to watery saturation, has throughout 

 the year more than ^ths of her hemisphere of sky con- 

 stantly cloudy, and there is hardly any perceptible differ- 

 ence between summer and winter. 



Madeira comes next for cloudiness, having -f^ths 

 cloudy on the mean of the whole year ; and if one solitary 

 month there has so little as T %ths of cloud, it is the cold 

 and windy month of March. 



Lisbon has an annual quantity of ^ths, but can show 

 that two of her summer months have, each of them, only 



