68 



NATURE 



[March 17, 192 1 



of the atmosphere disclosed by the observa- 

 tions. 



The difference between the two regions is that 

 in the lower region, the troposphere, the iso- 

 thermal surfaces may be roughly described as 

 horizontal, and in the stratosphere as vertical. 

 The sudden transition from the horizontal 

 sheet to the vertical sheet is the astounding 

 feature which is exhibited at the tropopause 

 all over the world; and as in the region of 

 vertical isothermal surfaces the horizontal tem- 

 perature gradient is from the equator towards 

 the pole, and therefore opposite to that of the 

 region where the isothermal surfaces are nearly 

 horizontal, the opportunity of drawing effective 

 attention to the paradoxical result of the equa- 

 torial region providing the coldest place on earth 

 ought not to be missed. There is at least as much 

 difference of temperature in the stratosphere 

 between the equatorial region and the pole in 

 one direction as there is at the surface in the oppo- 

 site direction, at any rate in the summer, and if 

 the upper region can be legitimately called iso- 

 thermal, why not the surface layer? 



It is remarkable that the chapters on the upper 

 air draw their information from observations of 

 the air of Europe. Our atmosphere has indeed 

 been worn rather threadbare. We have drawn 

 a number of conclusions from the European ob- 

 servations. They are largely confirmed by ob- 

 servations in Canada, and we are particularly 

 anxious to know whether they are confirmed or 

 contradicted by observations in the United States. 

 So far as information has reached us, it would 

 appear that the results for the United States show 

 rather high temperatures and high pressures when 

 brought into comparison with the observations of 

 the rest of the world. That would indicate a sort 

 of dislocation of the equatorial or tropical high 

 pressure to the northward over the southern 

 United States, at least in the summer. And as 

 such a dislocation had already been indicated, 

 years before the recent investigation of the upper 

 air, by Teisserenc de Bort in his computed map 

 of isobars at 4000 metres (which agrees in an 

 extraordinary manner with the results of modern 

 observations), we are naturally very curious to 

 have compendious summaries of all the results for 

 the United States, and to know whether the 

 generalisations which we have made apply to 

 them. 



This brings to mind a certain shyness about 

 tackling unsolved problems which other people 

 have recognised as fundamental but have failed 

 to solve. This shyness is a little bit characteristic 

 of Prof. Humphreys's work, and is a rather dis- 

 appointing feature of the book. One forms the 

 NO. 2681, VOL. 107] 



idea of a workman with a bag of nice, sharp 

 physical and mathematical tools who undertakes 

 with unerring success, any job that can be done 

 with the available implements, and who prefers 

 to pass by, with some irreproachable but vaguely 

 general remarks, a number of old problems which 

 Maury, Redfield, Espy, Loomis, Ferrel, and, later, 

 Bigelow tried to solve. This is the more to be 

 regretted because Prof. Humphreys's work, is 

 really original; it is not compilation. We get 

 the impression that, while possessed of almost 

 unexampled facility for dealing with it, he has 

 preferred to pass by on the other side when any- 

 thing controversial came within sight and there 

 was a chance of a row. As an example, optics, 

 which is an amenable subject, gets a whole part, 

 while sound, which is also physics, but not amen- 

 able, receives only a casual reference, and in the 

 chapter on the atmospheric circulation, on the 

 question of what actually steers the wind, a good 

 deal of space is given to discussion of the de- 

 flection due to the earth's rotation and change 

 of velocity with latitude, which is true enough" 

 in the vague sense that it supposes the air to be 

 free to find its path "under no forces," or with- 

 out constraint. We should prefer to start with 

 the fact that in actual practice wind is never free 

 from the constraint of the distribution of pres- 

 sure. Some meteorologists still require to realise 

 that if it were not for a certain suitable constraint 

 a train that started due north from New Orleans 

 would presently find itself running into the Atlan- 

 tic Ocean at a speed of a hundred or two hundred 

 miles an hour. Nobody really expects it to behave 

 in that way ; the flange sees that it does not : no 

 more does the wind ; pressure takes care that it 

 does not. Hence the introduction of uncon- 

 strained motion on the earth's surface requires 

 an apologia that is seldom forthcoming. 



We should like to pass on to Prof. Humphreys 

 the remark of a London street arab who found 

 us on one occasion hurrying to a cab to reach 

 some function that insisted upon an academic 

 robe which we were concealing so far as any- 

 thing scarlet can be concealed : " Put it on, sir ; 

 don't be shy." We share the feeling and appre- 

 ciate the dilemma, but we feel sure that if 

 Prof. Humphreys were less afraid of saying some- 

 thing that his academic colleagues might criticise, 

 he could render great service to the difficult science 

 of meteorology, even if the critics were correct. 

 Although ultimately the physics of the air is the 

 same as that in the laboratory, the physical prob- 

 lems of the atmosphere require special intellectual 

 tools for their solution, and the use of new tools 

 requires courage. One can, of course, keep out of 

 range of reproach for unorthodoxy or miscon- 



