DYNAMIC METEOROLOGY. 371 



air Ferrel gives especial attention to the effect of wave length upon the 

 law of (liminutioa in a complex bnndle of rays, such as those from the 

 snn, and shows that his formula and constants hold good for the visual, 

 the tliermal, and the chemical effects of the solar rays. (A special mem- 

 oir by him on radiation is published in the American Journal of Science, 

 July, 1889.) 



In chapter 2, on temperature of the atmosphere, Ferrel gives an ex 

 pression for the mean diurnal intensity of the sun's radiation developed 

 into a series as a function of the sun's declination and the observer's 

 latitude, which expression he also further converts into a series de. 

 pending on the time and the observer's latitude. With this he then 

 combines the effect of the absorption by the earth's atmosphere, and 

 proceeds to discuss the conditions that determine the temperature at 

 any place and any time for a body of any shape and coefficient of ab- 

 sorption and radiation. The importantresults obtained in this chapter 

 depend principally upon the radiation observations of Prevostaye and 

 Desains, Melloui, Langley, Duloug, and Petit, and are applicable to the 

 temperature of bodies at the earth's surface, the temperature shown by 

 thermometers and those shown by solar radiation apparatus. Especial 

 attention is given to the nocturnal cooling by radiation. (The late pub- 

 lications by Maurer, H. F. Weber, Angot and Zenker could of course 

 not be utilized by Ferrel.) 



In chapter 3 Ferrel deduces the general motions and pressure of the 

 atmosphere, beginning with the equations of absolute motion on the 

 earth at rest, whence follows his law that all bodies in motion are de- 

 flected to the right in the northern hemisphere. Combining these equa- 

 tions with the equation of continuity, certain general relations are de- 

 duced expressed by differential equations. 



Ferrel's method of solution of these equations consists in successive 

 approximations, beginning with the simplest cases of no friction and no 

 disturbance of the normal distribution of temperature, ho finally pro- 

 ceeds in section 4 of chapter 3 to give a special solution for the actual 

 case of the earth, which although only approximate yet within the limits 

 indicated, appears to agree well with observed ])henomena; this solu- 

 tion is summed up in the two following formuljc for the connection be- 

 tween the barometric gradient (G) expressed in millimeters per degree 

 of the great circle of the meridian from north to south, the angular dis- 

 tance(^) from the north pole or 90 degrees minusthe latitude; theveloc- 

 ity {v) of the east- west motions of a particle of air ; the total velocity (s) 

 of the particle; the temperature (r) on which the density of the air de- 

 pends ; the inclination {i) of the wind to the parallel of latitude ; the 

 observed barometric pressure (P) and the normal sea level barometric 

 pressure (Po). The resulting formula for the barometric gradient meas- 

 ured on the meridian, as given on page 207 of his " Recent Advances," is 



0.1571 V cos ^ P 0.1571 n cos P 



G= 



COS^ /(I + (Mr04 r j P„ ( 1+0.004 r) cos i Vo 



