758 Prof. J. H. Poynting on Prof. Lowell's Method for 



Table II. 



At 3550 m. above sea-level. Barometer 500 mm. 

 t — 0'6, fl! = 0-4, a=0'314. 



n. 

 1 



D/A. 



Rrf/S. 



Rn/S. 



R. 



9d/9. 



Bn/6. 



9/9. 



Range 



about 



300° A. 



1 



0-97 



0-37 



0-67 



0-99 



078 



0-89 



71° 



5/4 



4/5 



0-86 



0-26 



0-56 



96 



0-71 



0'84 



89° 



4/3 



3/4 



0-84 



0-24 



0-54 



0-98 



070 



0-83 



94° 



3/2 



2/3 



0-80 



0-20 



050 



0-95 



0-67 



0-81 



100° 



! 2 



1/2 



0-74 



0-14 



0-44 



0-93 



0-61 



0-77 



125° 



Table III. 

 At the level of Table II. and with t 



0-6, ai = 0% 

 but with d= 0*419 = 2/3 of 0-628. 



n. 



D/A. 



Rd/S. 



R»/S. 



R. 



Gd/9. 



On/9. 



081 



9/9. 



Range 



about 



300° A. 



1 



1 



1-02 



0-42 



0-72 



101 



091 



66° 



5/4 



4/5 



0-90 



030 



0-60 



0-97 



0-74 



0-86 



80° 



4/3 



3/4 



0-87 



0-27 



0-57 



0-97 



0-72 



0-85 



88° 



3/2 



2/3 



0-83 



0-23 



0-53 



0-95 



0-69 



0-82 



95° 



2 



1/2 



0-76 



0-16 



0-48 



0-93 



0-63 



0-75 



120° 



The third table is only given to show that the change in 

 the value of a does not greatly affect the results. The value 

 of a of Table II. is much more reasonable if that of Table I. 

 is near the truth. We need, therefore, only compare the 

 results given in the first two tables. 



If we take the same values of n in each table the value of 



R is less at the higher level than at the lower in every case 

 except that in which n has the extreme and probably inad- 

 missible value of 2. The value of 6 is less at the higher 

 level in every case. But it appears most probable that 1/n 

 or D/A is greater at the lower level than at the higher. 

 For consider a thin layer of air at sea-level. It is radiating 

 equally up and down, but of the half going upwards a con- 

 siderable fraction will be intercepted by the superin- 

 cumbent and strongly absorbing layers. Now consider a 



