PROGRESS OF METEOROLOGY IN 1889. 21o 



of the air thermometer and its relation to the absolute thermo dynamic 

 scale, the normal mercurial and its reductions to the air thermometer, 

 and ordinary thermometers with their reductions to the normal mer- 

 curial. After the theory of the instrument, the subject of thermometer 

 exposure is treated wicli corresponding fullness, and the conditions 

 necessary for obtaining the true air temperature are clearly set forth. 

 Chapters on miscellaneous forms of thermometers and on thermographs 

 complete the section. Tlie third section— that treating of the motion 

 of the air — also commands special attention on account of the origi- 

 nality and depth of its treatment. The results of a large amount of 

 research in theoretical and experimental hydrodynamics are discussed 

 in their relation to the theory' of the action of the different classes of 

 anemometers. The last chapter of the section takes up the various 

 methods of measuring upper currents by means of observations of 

 clouds, and describes the different methods of using the nephoscope. 

 The section on hygrometry gives a similarly complete exposition of 

 the theory of the psychrometer. 



A Popular Treatise on the Winds, by William Ferrel. — " It is with no 

 ordinary degree of satisfaction that we hail the publication of Professor 

 Ferrel's treatise. The work is a ''popular" treatise, but popular only 

 in the higher sense of the word. A system of movements so complex 

 as those ot the earth's atmosphere can not bo made clear io any one who 

 is not capable of following a chain of close reasoning, or who is not pre- 

 pared to bring to the study that concentrated attention that is requisite 

 to master any problem in deductive science. 



" The most important and original portion of the book is that which 

 deals with the general circulation of the atmosphere, in relation to 

 which the cyclones and anticyclones that cause the vicissitudes rf 

 local weather are but matters of subordinate detail. The magnitude of 

 the work achieved by Professor Ferrel in this field has hitherto been 

 recognized only by the few. It is not too much to say that he has done 

 for the theory of atmospheric circulation that which Young and Fresuel 

 did for the theory of light ; and that the influence of his work is not more 

 generally reflected in the literature of the day must be attributed to 

 the want of some ])opular exposition of the theory. 



" Starting with the fundamental conditions of a great temperature dif- 

 ference between equatorial and polar regions and a rotating globe, and 

 postulating in the first instance a uniform land or water surface, it is 

 shown how the convective interchange of air set up by the former must 

 result in producing two zones of maximum pressure in about latitude 30° 

 in both hemispheres, two principal minima at the poles, and a minor 

 depression on the eciuator, together with strong west winds in middle 

 and high latitudes, and an excess of easterly winds in equatorial re- 

 gions. The two troi)ical zones of high pressure determine the polar 

 limits of the trade winds, and the whole system oscillates in latitude 

 with the changing declination of the sun. Further, as a consequence of 



