74 Roijal Society. 



amount of inclination, as at Hobarton and Toronto, both in sunniier 

 and winter, but it diminishes the dip at places which are within the 

 tropics, and with little inclination, as St. Helena. By other kinds of 

 observations, it appears to be in advance of the sun. All the pheno- 

 mena indicate that the sun does not act directly on the needles at 

 ditlerent places, but mediately through its effect on the atmosphere. 

 The author then considers the possible cause of numerous irregu- 

 lar variations, such as those that are shown by the photographic pro- 

 cesses of record at Greenwich and Toronto. The varying pressure of 

 the atmosphere, the occurrence of winds and large currents of air, of 

 rain and snow, of the passage of those masses of warm and cold air 

 which the meteorologist recognizes in the atmosphere, of the aurora 

 borealis, he considers may all produce changes in the lines of mag- 

 netic force, and become more or less sensible in the records of 

 irregular variations. The author thinks it very possible that masses 

 of air at diflerent temperatures may be moved by the magnetic force 

 of the earth, according to the principles of differential action made 

 manifest in the experiments on warm and cold oxygen, in which 

 case material as well as potential magnetic storms may exist. He 

 concludes his paper by calling attention to the wonderful constitu- 

 tion of oxygen in its magnetical and electrical, as well as its chemical 

 relations, to the offices it has to perform as part of the atmosphere. 



4. " Experimental Researches in Electricity." Atmospheric Mag- 

 netism, continued. Twenty-seventh Series. By Michael Faraday, 

 Esq., D.C.L., F.R.S. &c. Received November 19, 1850. 



In order to obtain an experimental representative of the action of 

 the atmosphere when heated above or cooled below the average 

 temperature, the author employed a ring helix of covered copper 

 wire, through which an electric current was passed. The helix was 

 about one inch and a half in diameter, and having the well-known 

 system of magnetic forces, was placed with its magnetic axis parallel 

 to a free needle : when its position was such that a needle within 

 the ring would point with the north end downward, then the eff"ect in 

 deflecting the surrounding lines of force of the earth was considered 

 as like that of a relatively paramagnetic mass of air; and when its 

 position was reversed, its action was representative of that of a heated 

 or relatively diamagnetic mass of air. Bringing this helix into the 

 vicinity of small magnetic needles, suspended either freely, or so as 

 to show declination or inclination, the planes of action or indif- 

 ference as regards the power of deflecting the lines of force and the 

 needle were observed. When the needle can move only in one 

 plane, there are four quadrants, formed (in the case of the de- 

 clination needle) by the intersection of the planes of the magnetic 

 equator and meridian. When in these planes there is no deflection 

 at the needle, but when in the quadi'ants there is, and in opposite 

 directions in the neighbouring quadrants. 



As the lines of force are held in and by the earth, so these experi- 

 ments were repeated with a needle in near vicinity to a magnet, and 

 the dilference of effect is pointed out : then the extent to which these 

 results are applicable to those of the earth is considered, and their 

 utility in guiding the inquirer. 



