424 



Results of Makerstoun Observations, 1844. 



TABLE XXIII. — Extreme Readings of the Barometer for each Month ; Extreme Mean Daily Heights 

 for each Month ; and Extreme Dim'nal Ranges for each Month, together with the Ranges and 

 Means of the Extremes. 



The highest barometer occurred Dec. 21'' 8^ 



The lowest Feb. 25d IS"- 



Extremes of Atmospheric Pressure for 1844. 



n. 



.ODD -i in. 



,lll } Range = 6-774. 



The liighest daily mean pressure occurred Dec. 21'' =30-314 1 „ _. „„^ 



Thelowest Oct. IS^ =28-619 ] "'''°§''- ^■''^^• 



The highest monthly mean pressure occurred in May =29-980 "1 „ _r>.o^q 



Thelowest Feb. =29-321 J '^ ~ 



The greatest range of pressure in a civil day occurred February SS** =0-738. 



The least July 2"i and September 25'' = 0-031. 



Mean = 29-446. 



Mean = 29-466. 



Mean = 29-650. 



Pressure of Dry Air. 

 Annua! Variation of the Pressure of Dry Air. — If we assume that the means at the foot of Table X. 

 accurately represent the pressures of the vapour of water in the atmosphere, the mean pressm-es of the dry 

 air will be obtained by subtracting them from the means for the total atmospheric pressure. Table XVIII. The 

 resulting mean pressures of di-y air ai-e as follow : — 



in. .Tan. Feb. March. April. May. .Tune. July. Aug. Sept. Oct. Nov. Dec. 



29 I -477 -141 -320 -547 -707 -273 -258 -134 .466 -121 .305 -705 

 r The least mean pressures of di-y air are those for October, August, and February, and the greatest are those 

 for May and December. The means vary in the same manner as those for the total atmospheric pressure. 



Diurnal Variation of the Pressure of Dry Air. — The followmg Table contains the diui-nal variations of 

 the pressure of di-y air, obtained fi-om a comjjarison of Tables XIII. and XXII. 



The variation of the pressure of the dry air thus determined is doiible in winter, like that of the total 

 pressure ; there is a secondary maximum and minimum in autumn, and the variation is single, \vith some irre- 

 gularities, in the other quarters, and for the year. The epochs of maxima and minima are as follow : — 



Max. 



Winter. Nov., Dec, Jan., + 9'> 40™ p.m. 



Spring. Feb., March, April,... 9'' 10™ p.m. 



Summer. May, June, July, 



Autumn. Aug., Sept., Oct., ... -f 11'' 10™ p.m. 

 The year 1844, 12'' 10™ a.m. 



The law of variation is so different in the different quarters of the year, that no confidence should be 

 placed in these residts, as exhibiting the diui-nal variation of the pressure of di-y air : it appears extiemely 

 probable that the true pressure of aqueous vapour in the atmosphere is not to be determined by means of the 

 psychrometer. 



