2 OS ^ 



the well-kii()\vii siMiii-diiinial period in the pressure, the atmosplieric 

 eleelricih, ihc xapoiir leiisioii aiid die alisoliite huniidily, disa|)pears 

 in j)r(jp(Hli()ii as higher hivci's of die air are exaniincd and j-esolxcs 

 itself into a simple diurnal period. ha\ inu' ils ndniniuni al>oul 3'' a. ni. 

 and its niaxinium at o'' p. ni. 



However il is onlv in rcccid years tiial a svsleniade in\esliualioii 

 of the hi,i>li(M' layers of die aimosphcre has heen undertaken, ]>rin- 

 eipalh' in X. America and in (iernuuiv, and the results puhlished 

 until now are iusuflieienl to dechice from diem the eosmie jieriods. 

 xlnvhow, die same annual variation as dial uhieli marks the pohir 

 li<'lits and the terrestrial mai'-netism has h(>en ohser\ed in die diurnal 

 oscillation of haroinelrie prt^ssure near die surface, notwithstandiuu- the 

 complexilv of the inilneiices ther(> at work. 



The lahle hei'e snhjoined, taken from the haiuihook of Ahkuf.nhs 

 p. (i03, <>'ives the mean ami>litude of the semi-diurnal oscillations of 

 the Itaromeier, e\pl•e^sed in in. m.. foi- the follow in,u- |)laces: 



1) L'psala 59°52' n. lat.. 2) Leipzig bV-JiV n. lat., 3) Munich 

 48"9' 11. lat., 4) Klagenfurt 4(r37' n. lat., 5) Milan 45 28' n. lai., 

 C) Rome 4r52' n. lal., 7) 22*^30 s. lal., 8) 10° n. lat. 



Jan. Febr. Mrcli Apr. May. June. July. Aiiii Sept. Oct. ! Nuv. | Dec. Ytvu- 

 \) ().!:>, ii.u u.ir) (M(; o.li;().l:'. o.l:'. o.i-i^O.17 0.1.J oil e.K) o.i:'. 



li) O.IC) 0.^20:0.24 0.271 0.-v'i 0.20 



:?) 10.21 0.2:1 



") 



o.2:>. 29 

 o.:i() 0..% 

 o.:?o i).:i3 



O.C..") 0.(;8 

 O.TOlO.FO 



0.28 0.£J>().28 

 0.35 0.20 10.20 



0.20 

 O.20 



0.38 I 0. SO I 0.30! 0.20 

 0.35 ' 0.32 !). 29 20 



0. 70; 0.08 1 0.04 



0.8:{ 



0.82 10.73 



01 

 0.0.-) 



0.21 

 0.25 

 0.34 



0.23 

 0.20 

 0.27 



0.29:0 31 

 0.20 

 0.()3 

 . 05 



0.27,0.22 0.21 ().IG 0.22 



0.28' 0.27 0.21 0.21 I 0.25 



0.27 0.2'i 0.21 1 0.24 0.27 



|>.32 0.33 0.31 29i0.:;2 



! I 



0.35 0.3(5 0.33^0.29 0.31 



09 '0.00 0.G7 



1 

 0.82' 79 0.7c. 



30 



0.0()| 72 72 



0,09 I 0.75 0.78 



It will he seen that the maxima again coincide with the equino.xes; 

 that the winter niinimum for places al>o\(' 45' lal. is lower than the 

 summer minimum, thus agreeing in e\'erv respect with the pei-io- 

 dicitv descril)ed under J. Il is indeed easy to understand that die 

 amplitude of the lluctuations in the atmospheric pressure will increase 

 or decrease according as the \ ariahility of the illumination increases 

 or decreases. The circumstance thai in lesser latitudes, north as well 

 as south of the ei[uator, the July minimum seems lowest, isascrihed 

 bv Akrhknus to the fact that the Kartli is at thai time farther away 

 from the Sun than in Januarx. 



