1000 



sun. On examining the results at Toronto, corresponding effects 

 were found to occur, when the upper or south end of the needle was 

 considered, and therefore in accordance with the hypothesis. The 

 examination of the observations made at Greenwich, Washington, 

 Lake Athabasca, Fort Simpson, and St. Petersburgh, are considered 

 as further adding confirmation. By the aid of these observations the 

 author restates his principles more minutely, endeavouring to indi- 

 cate what difference, changes in the inclination, declination, place 

 of the sun, land, and sea, &c. will produce. 



Though the sun is the cause of those changes in the atmosphere 

 which affect the lines of force of the earth, he is not assumed as the 

 centre of action as regards those lin<>s ; that is considered to exist 

 somewhere in the atmosphere. It appears to be in the upper re- 

 gions and not on the surlace of the earth, because it increases the 

 dip of places north and south of the tropics which have a certain 

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

 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. Ail the pheno- 

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

 different 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 different 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., RR.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 effect in 

 deflecting the surrounding lines of force of the earth was considered 



