Intelligence and Miscellaneous Articles. 75 



The effect of heated air having been considered in the last paper, 

 that of cold air is now taken up; and after considering its action in 

 causing a contraction or drawing together of the terrestrial lines of 

 magnetic force, according to the principles of conduction before 

 enunciaied, the author considers generally where the regions of cold 

 which travel round the earth every twenty-four hours will be in 

 the northern and southern hemispheres, and how they will grow up 

 and diminish in extent and importance as the sun moves north and 

 south during the year. After which he applies these considerations, 

 and the results of the experiments Avith the ring helix, to the expli- 

 cation of the changes of the needle as they are given by observations 

 at St. Petersburgh, Greenwich, Hobarton, Toronto, Cape of Good 

 Hope, St. Helena and Singapore. In doing this, he endeavours to 

 explain the night action, tlie early morning eftect, the contrary 

 course of the needle for the same hours in different months, the dif- 

 ference of local time dependent on the distribution of land and 

 water, the cumulative effect of preceding months, and the con- 

 tinual effect, especially in the tropical regions, of the higher tempe- 

 rature of the northern hemisphere above that of the south. In all 

 these points the autlior sees such an agreement between the natural 

 results and those which are suggested by the assumed physical cause 

 of the magnetic variations, as to give him a growing confidence in 

 the truth of the views he has put forth. 



XI. Intelligence and Miscellaneous Articles. 



0\ THE CHEMICAL COMPOSITION OF THE AIR. BY M. LEWY. 



I^'HE author states, that ever since the month of March in the pre- 

 sent year, he has been occupied with the analyses of the air, taken 

 in the City of Santa- Fe de Bogota, and that he has lately arrived at 

 very extraordinary results, relating to the proportion of carbonic 

 acid. He found, in August and September, 47 volumes of this acid 

 in 10,000 volumes of air, whereas in the months of March, April, 

 May, June and July, the quantity of carbonic acid never exceeded 3 

 to 4 volumes in the same quantity of air. The author states that 

 he places perfect reliance on his experiments; all having been per- 

 formed according to the most exact methods. 



M. Lewy's experiments on atmospheric air, collected at the sur- 

 face of the Atlantic Ocean during his voyage, have developed a fact 

 which is new and very general, and appeared in every analysis ; it 

 is, that the air taken during the day contains more oxygen and more 

 carbonic acid than the air taken during the night ; this difference 

 of composition, the author is of opinion, has not hitherto been ob- 

 served ; all his analyses, without exception, confirm this result, that 

 there is more carbonic acid and more oxygen during the day than in 

 the night, and the differences are more marked in clear than in foul 

 weather. 



M. Lewy gives tlie results of two analyses of air at a great di- 

 stance from land, taken at random : — 



December 18th, 1847, 3 i'.m. : weather fine ; wind east, strong 



