ATMOSPHERIC PRESSURE. 



217 



Diurnal fluctuation of the baronietcr. 





(+ above mean, — below mean reading.) 







Port Foulke 



Van Rensselaer 



Port Kennedy 



Baffin Bay 





t = 780 18'. 



780 37'. 



720 01'. 



720 30'. 



2 .... , 



—0^006 



0^000 



—0^019 



— 0'°.010 



i 













—.004 



+ .001 



—.028 



—.013 



6 













—.012 



+ .001 



—.031 



—.017 



8 













+.002 



—.003 



—.002 



—.012 



10 













—.002 



—.001 



+ .010 



+ .007 



Noon 













—.004 



—.002 



+ .008 



.000 



2 













—.004 



—.006 



+ .011 



+.002 



4 













+ .001 



—.002 



+ .014 



+ .010 



6 













+.011 



+.002 



+ .015 



+.013 



8 













+.005 



+ .004 



+ .018 



+ .013 



10 













+ .007 



+.006 



+ .009 



+ .010 



12 













+ .005 



+.003 



.000 



.000 



Expressed analytically the above diurnal fluctuations are given by the equations: — 



Port Foulke, h = 0".006 sin (9 + 159°) + 0'".004 sin (2« + 186°) 



Van Rensselaer Harbor, b= 0.003 sm (s + 110 ) +0.002 sm (29 + 204 ) 

 Port Kennedy, b = 0.021 sin {e + 202 ) +0.009 sin (29 + 150 ) 



Baffin Bay, b = 0.013 sin (9 + 185 ) +0.004 sin (2e + 159 ) 



The angle 6 counts from midnight at the rate of 15° an hour. 



The general correspondence of these expressions is quite satisfactory ; the most 

 striking feature is the rapid diminution of the diurnal fluctuation with an increase 

 of latitude ; thus the coeflicients of either term for Van Eensselaer Harbor are one- 

 half of those for Port Foulke, and taking the average for these localities (^^78° 28') 

 we have a diurnal range of only 0.013 inch, whereas the upper range for Port 

 Kennedy and Baffin Bay (^:=72° 15') is 0.038 inch; if this rate of diminution 

 continues, the range would be less than 0.001 inch in latitude 81|°. 



The observed and computed diurnal fluctuation at Port Foidke is shown by the 

 annexed diagram. 



DiUENAL FlUCTDATION OF THE AtMOSPHEHIC PRESSURE, 



By the aid of the curve we find the maximum to occur about 6| P. M. ; at Van 

 Rensselaer it occurred about 10 P. M., and at Port Kennedy and Baffin Bay about 

 7| P. M. ; the principal minimum occurs about 3 A. M., at Van Rensselaer the 

 (secondary) minimum occurred about 4 A. M., and at Port Kennedy and Baffin Bay 



2S December, 1865. 



