356 SCIENTIFIC RECORD FOR 1884. 



and the progress of depressions so that the direction of the movement 

 forms an angle with the direction of the greatest rise of temperature, 

 which angle varies between 45 and 90 degrees, being greater in summer 

 than in winter, the highest temperature being on the right-hand side of 

 the storm path. This principle is also indicated by Clement Ley in the 

 following words : "The direction of progress of depressions in Western 

 Euroi)e varies in Europe between north-northeast and south southeast, 

 and is primarily dependent on the preceding general distribution of 

 temperature, so that the movement is inclined at an angle of 45 degrees 

 to ihe lower isotherms." These principles, announced 11 years ago in 

 England, have, says van Bebber, not found the proper consideration in 

 European weather predictions. After some explanatory words, he sums 

 them both up in the following : The progress of depressions takes place 

 approximately in the direction of the prevailing movement of the whole 

 mass of air in the neighborhood of a depression. This statement would 

 seem to support the assumption that the atmospheric whirl is carried 

 along by the i)re vailing current of air. [We are now giving van Bob- 

 ber's statements nearly in his own words and reserve the privilege of 

 stating that, although the connection between the phenomena is very 

 nearly as he gives it, yet the rationale of the process is, we think, not 

 at all as he seems to suggest.] By reducing pressures upwards and 

 constructing isobars for an altitude of 2,500 meters and also for 

 higher altitudes, he is led to the conclusion that the whirlwind move- 

 ment is confined only to the lower strata of air, that the axis of the 

 whirl is inclined to the left and slightly towards the front, and that the 

 upper currents of air in the neighborhood of the whirl have nearly the 

 same direction, so that those belong to a great ring progressing with 

 the depression and in which the air that rises within the depression now 

 sinks again. This agrees with the fact that the movement of the cirrus 

 clouds agrees with that of the progress of the depression ; this al-o ex- 

 plains why the upj^ter clouds, which also move with the depression, are 

 so prominent in advance, while on the left side of the path the cirrus 

 clouds are so infrequent ; this also explains why the principal storm 

 l)aths marked out by van Bebber are especially followed in the colder 

 season of the year and why the storm paths, numbered 1 and 4 by him, 

 moving towards the northeast or east-northeast, occur most frequently 

 in the warm season. Equally easy is it to explain why a number of suc- 

 cessive storms have a tendency to follow the path pursued by some prom- 

 inent leading one, for if atmospheric pressure and temperature are so 

 distributed over a large part of the hemisphere as to be favorable to 

 the production of a given storm path, then it is clear that succeeding 

 depressions will follow the same path so long as the distribution of 

 temperature and pressure does not change, and as these changes can 

 only go on slowly it necessarily'' happens that storms and local weather 

 changes some times show great similarity for days and weeks together. 

 381. [It is certainly to be regretted that the intense study under most 



