200 



EECREATIYE SCIENCE. 



same place, does not always pass over tlie 

 same spot ; local circumstances, of wticL. we 

 cannot at present form any correct ideas, 

 operate in causing a variation in the direction 

 of the currents in the variable wind districts. 

 The polar and equatorial currents combine, 

 and, as the one or the other prevails, we have 

 a northerly or a southerly wind. That the 

 wind must always blow in circles is evident 

 from the variability of the wind itself. In 

 England, at the 'same moment, we can have 

 the wind blowing from every point of the 

 compass. These circles will vary very much 

 in diameter. There are many influences 

 exerted to alter the direction of the wind, 

 and the temperature of the mass of air borne 

 along by it. Hills and mountains can change 

 the direction of a current, whilst a mass of 

 air, of a certain heat, will become altered in 

 its temperature by simply passing over a 

 cold or a warm district. 



Moisture is another element which is 

 always present in the air ; at one time pass- 

 ing over us as invisible vapour, at another 

 visible as a cloud, and at a third discharging 

 rain, or, if at a low temperature, frozen into 

 hail or snow. In studying the clouds atten- 

 tively, we learn many curious facts with re- 

 gard to their forms and positions. Clouds 

 chiefly move in circles, and this is seen from 

 the tendency they have to form in straight 

 lines, i. e., converging to a point in the far 

 distance, and the reason they are seen as 

 straight lines is owing to these circles having 

 a diameter, too large to be seen, curved in 

 our limited view of them. Lines of cirri, con- 

 verging to the north near Nottingham, have 

 been observed at the same time converging to 

 the north-west at Manchester. Clouds have 

 been said to owe their form to currrents of air, 

 and, in some degree, perhaps, this is true, as is 

 shown by the clouds presenting their pointed 

 ends to the wind ; yet there is another more 

 powerful force exerted, a power inter se, 

 which, in rare instances, has been well shown 

 from this observatory. Clouds have been 



seen to be moved in one direction by the 

 wind, and, at the 

 same time, currents 

 (within the cloud 

 itself) moving the 

 mass of the cloud 

 in an opposite di- 

 rection. See Fig. 2, 

 where c is a cloud 

 moving in the di- 

 rection of the ar- 

 rows, A A, having 

 a spiral progressive 

 motion in the di- 

 rection of the ar- 

 rows, B B. "Whilst 

 writing this article, 

 a very singular ex- 

 ample was noticed. 

 A cumulus (Fig. 3) 

 floated in the direction a a, having two 

 motions within it at its two extremes, the 

 one in the one direction, b b, and the other in 



Fig. 2. 



Fig. 3. 



the opposite direction, d d. This is also shown 

 in thunder-storms, when the whole cloud can 

 be well observed ; instead of the cloud dis- 

 charging rain from all portions, it will be 

 discharged only from a particular part (see 

 Fig. 4). It is also shown by the same cloud 

 discharging rain from one portion and hail 

 from another. In most storms there is a 

 belt of frozen rain (or hail), and this is, at 

 the first portion of the storm, probably owing 

 to the colder heavier air rushing to the 



