548 ' REPORT — 1903. 



habits. But unfortunately the travellinf^ depression cannot be said to preserve 

 its identity in any sense to which quantitative reasoning can be applied. As long 

 as we confine ourselves to a comparatively small region of the earth's surface the 

 travelling depression is a real entity, but when we widen our area it is subject 

 to such variations of path, of speed, of intensity, and of area that its use aa a 

 meteorological unit is seriously impaired, and when we attempt to trace it to 

 its source or follow it to its end it eludes us. Its origin, its behaviour, and its end 

 are almost as capricious as the weather itself. 



Nor if we examine other cases in which a veritable entity is transmitted can we 

 expect that the simple barometric distribution should be free from inexplicable varia- 

 tions. "We are familiar Avith ordinary motion, or, as I will call it, astronomical 

 motion, wave motion, and vortex motion. Astronomical motion is the motion of 

 matter, wave motion the motion of energy-, vortex motion the motion of matter 

 with energy, but the motion of a depression is merely the transmission of the 

 locus of transformation of energy ; neither the matter nor the energy need 

 accompany the depression in its motion. If other kinds of motion are subject 

 to the laws of conservation of matter and conservation of energy, the motion 

 of the depression must have regard also to the law of dissipation of energy. 

 An atmospheric disturbance, with the production of rainfall and other thermal 

 phenomena, must comply in some way with the condition of maximum entropy, 

 and we cannot expect to account for its behaviour until we can have proper 

 regard to the variations of entropy. But the conditions are not yet in a form 

 fcuTtable for mathematical calculation, and we have no simple rules to guide 

 us. So far as Meteorology is concerned, Willard Gibbs unfortunately left his 

 work unfinished. 



When the cyclonic depression was reluctantly recognised as too unstable a 

 creature to carry the structure of a general theory Mr. Galton's anticyclones, 

 the areas of high pressure and descending currents, claimed consideration as 

 being more permanent. Professors Koppen and van Bebber have watched their 

 behaviour with the utmost assiduity and sought to find therein a unit by which the 

 atmospheric changes can be classified ; but I am afraid that even Dr. van Bebber 

 must allow that his success is statistical and not dynamical. ' High pressures ' 

 Ibllow laws on the average, and the quantity we seek is not an average but an 

 individual. 



The question arises, whether the knowledge of the sequence of weather changes 

 must elude us iiltogether, or will yield to further search. Is the man in the 

 street ri"ht after all ? But consider how limited our real knowledge of the facts 

 of atmospheric phenomena really is. It may very well be that observations on the 

 surface will never tell us enough to establish a meteorological entity that will be 

 ^ubiect to mathematical treatment; it may be that we can only acquire a know- 

 ledge of the general circulation of the atmosphere by the study of the upper 

 air, and must wait until Professor Hergesell has carried his international organisa- 

 tion so far that we can form some working idea therefrom of general meteoro- 

 loo^ical processes. But let us consider whether we have even attempted for surface 

 meteorology what the patience of astronomers from Copernicus to Kepler did for 

 astronomy. 



Do we yet fully comprehend the kinematics of the travelling depression ; and 

 if not, are we in a satisfactory position for dealing with its dynamics ? I have 

 lately examined minutely the kinematics of a travelling storm, and the results 

 have certainly surprised me and have made it clear that the travelling depressions 

 are not all of one kinematical type. We are at present hampered by the want of 

 really satisfactory self-recording instruments. I have sometimes thought of 

 appealing to my friends the professors of physics who have laboratories where the 

 reading of the barometer to the thousandth of an inch belongs to the work of the 

 'elementary class,' and of asking them to arrange for an occasional orgy of simul- 

 taneous readings of the barometer all over the country with corresponding 

 weather observations for twenty-four consecutive hours, so that we might really 

 Icnow the relation between pressure, rainfall, and temperature of the travelling 

 depressions ; but I fear the area covered would even then hardly be large enough, 

 and we must improve our self-recording instruments. 



