452 



DR RUCHAN AND MR OMOND ON THE 



curve is distorted by the expansion and contraction of the air below the level of the 

 summit, due to the diurnal changes of temperature, which adds to the total amount 

 of air weighed by the barometer there during the daytime and subtracts from it at 

 night, thus reducing the afternoon minimum and increasing the morning one. But 

 the changes induced on this distorted diurnal curve by the selection of fine and cloudy 

 days are of exactly the same nature as at the other stations in the temperate zone. 



The results of selecting fine or cloudy days are perhaps best seen in the subjoined 

 table, which gives, first, the difference of the annual fine day curve from the annual 

 general curve at each station ; and, second, the same difference for the cloudy days. In 

 each case where the barometric reading is raised the amount in thousandths of an inch 

 is given in bold type, and where it is lowered, in italic. It is at once evident that the 

 selection of fine days raises the barometric means in the forenoon and lowers them at 

 night, while cloudy days have the opposite effect at virtually all the stations. 



Difference of Fine Day Annual Means from General Annual Means. 

 Excess of fine in bold type and defect in italic type. 





1 



2 



3 



4 j 5 



G 



7 



8 



4 

 5 

 6 

 9 



4 

 12 

 6 

 8 

 7 



9 



2 

 4 

 5 

 9 



6 



12 

 5 

 7 



11 



10 





 3 



4 

 9 



7 

 11 



7 



5 



15 



11 





 2 

 3 

 8 



8 

 9 

 4 

 5 

 16 



12 



2 

 1 

 4 

 6 



9 



7 



4 



1 



18 



13 



4 

 1 

 3 

 5 



8 

 5 

 2 

 

 18 



14 



4 

 1 

 2 

 4 



8 

 3 



3 



1 

 16 



15 



4 

 3 

 

 1 



6 

 



1 



2 



15 



16 



5 



4 

 1 

 1 



4 







3 



14 



17 



5 



4 



2 

 2 



3 



3 



2 



4 



10 



18 



3 

 6 

 3 

 3 



2 



5 



5 

 7 



19 



1 

 6 



4 

 4 

 1 

 5 

 3 

 9 

 4 



•20 



1 

 5 

 4 

 5 



3 

 6 



4 

 5 

 2 



21 





 5 

 4 

 6 



5 

 7 

 6 

 4 



6 



22 





 3 

 5 



7 



6 



9 



7 



3 



13 



23 



1 



f> 



6 

 9 



10 



10 



8 



4 

 22 



Mid- 

 night. 



Mean. 



San Jose 

 Hong Kong . 

 Trieste . 

 Magdeburg . 



Ben Nevis 

 Fort William 

 Sodankylii 

 Bossekop 

 Jan Mayen . 



2 







4 

 8 



11 

 10 



7 

 6 



m 



2 

 2 



2 

 7 



8 

 6 



4 



3 



20 



2 

 2 



1 

 4 



6 

 3 











16 



2 

 4 

 1 



1 



3 

 

 3 

 3 



13 



3 

 5 

 3 

 2 



2 



3 



6 

 4 

 8 



4 

 4 

 5 

 5 



1 



7 



7 

 7 

 2 



4 

 5 

 6 



7 



2 

 9 

 8 

 9 

 3 



1 



1 



6 



11 



12 

 14 



11 



5 

 30 



•003 

 •031 

 125 

 •093 



159 

 180 1 

 160 

 140 

 150 



Difference of Cloudy Day Annual Means from General Annual Means. 

 Excess of cloudy in bold type and defect in italic type. 





i 



2 



3 



4 



5 



6 



7 



8 



9 



10 



11 



12 



13 



14 



15 



16 



3 

 6 

 1 



2 



3 

 2 

 5 



1 

 9 



17 



2 

 6 



4 

 3 



j 



5 

 4 

 2 

 9 



18 



2 

 6 

 4 

 4 





 5 

 3 



4 

 6 



19 



1 



4 



7 

 4 



2 

 6 

 4 

 3 



5 



20 



1 



3 



6 



4 



4 

 7 

 1 

 6 

 1 



21 





 2 

 7 

 5 



5 

 8 



1 

 7 

 4 



22 





 3 

 6 

 6 



9 

 9 

 1 

 8 

 8 



23 



1 

 1 



7 

 6 



9 



10 







9 



11 



Mid- 

 night. 



Mean. 



•002 

 •031 



■135 

 ■020 



•130 

 ■134 

 ■030 



■027 

 ■081 



San Jose 

 Hong Kong . 

 Trieste . 

 Magdeburg . 



Ben Nevis 

 Fort William 

 Sodankylii . 

 Bossekop 

 Jan Mayen . 





 2 

 5 

 6 



8 

 8 

 2 

 9 

 11 



1 



2 

 2 

 4 



4 

 4 

 3 

 4 

 11 



4 

 5 

 2 

 1 



3 



1 

 3 

 1 

 8 



4 

 4 

 5 

 



1 



4 



4 



> 



8 



3 

 5 



6 

 2 





 7 

 3 

 6 

 7 



3 

 5 

 7 

 5 



2 

 8 

 3 

 8 

 3 



2 

 5 

 8 

 6 



4 

 10 



4 

 9 

 



3 

 5 

 9 

 8 



4 

 10 



3 



10 



1. 



1 



4 

 7 

 9 



6 

 11 



2 

 10 



4 



1 



2 



4 

 8 



6 

 9 

 

 7 

 5 



1 



I 

 3 

 7 



G 

 8 

 

 6 

 8 



1 





 3 



5 



6 

 6 

 3 



6 

 8 



2 





 3 

 3 



6 

 3 

 3 

 4 



9 



4 

 4 



2 







4 





 4 



2 

 10 



5 

 5 



1 

 



4 





 5 



1 

 10 



1 



11 

 8 



12 



11 



1 



12 



16 



Thus on fine days there is superimposed on the ordinary diurnal curve a single period 

 curve with its maximum somewhere between 7 a.m. and 9 a.m. and its minimum at 



