ON VARIATIONS IN DIRECTION AND MOTION OF THE AIR. 271 



tion takes place throughout the year, and that no period can he regarded 

 as calm. The early part of January is, however, much calmer than might 

 he expected, while the latter portion of that month and beginning of 

 February are just the reverse, as is also March. The great increase ob- 

 servable in the portion of the diagram that shows the amount of motion of 

 the air that passes Liverpool at the end of June and beginning of July, is 

 due to the very strong W., W.N.W., and north-westerly currents at that 

 period of the year. At Wrottesley the same currents exist, and at the same 

 period, but their violence is so much diminished as not to disturb the general 

 averages. 



These observations seem to indicate, both from the diagrams of each day 

 as well as from those exhibiting the horary variations, that there are three 

 principal currents or groups of winds that may be classed together. First 

 the north-easterly, prevailing mostly in the spring, and also appearing in 

 the autumn. Whether they may be regarded as a temporary extension of 

 the trade-winds will require further observations to determine. They possess 

 some of the characteristics of that wind. 



The next group is the great south and south-westerly current, or anti- 

 trade-wind, the peculiar horary variations of which and periods of greatest 

 motion have already been referred to. 



The currents from the N.W., including those from "W. to N.N.W., form 

 the last group. 



Although the north-west and south-west groups are in many respects 

 distinct from one another, yet they often blend so much that it is not pos- 

 sible to draw a definite line between them. 



Further observations on a more extended scale are required to define with 

 accuracy the periods of prevalence or otherwise of the various currents, and 

 to determine many interesting points regarding their course and action, 

 which can now be only dimly shadowed forth. It is, however, hoped that 

 what has here been done will aid in showing the importance of keeping a 

 constant record of the movements of the air over as large an area of the 

 earth's surface as can with convenience be arranged. The geologist, whose 

 researches also extend over the whole earth, finds in the great globe itself a 

 vast registering instrument, where the changes that he is studying have been 

 permanently written, enabling him at his leisure to examine its records, and 

 refer to periods so immeasurably distant that he may, by reversing his train of 

 thought, have glimpses of eternity. The meteorologist, on the contrary, finds 

 himself lost by reason of the ephemeral nature of the forces and conditions 

 which he has to deal with ; he requires all the artificial appliances that can 

 help him, to take note of and record the various changes that occur ; but of 

 all the conditions, there are none more important than those of the great cur- 

 rents of the atmosphere. A knowledge of the quarter from which the air 

 arrives at given points on the earth's surface, and the duration of the current, 

 will be a key to its various conditions of temperature, humidity, weight, and 

 all the other features it may possess ; while to trace it onward, over a large 

 area, will materially aid in unravelling the secrets of the producing causes, 

 and the laws that determine its course. 



