Prof. Hansteen's New Chart of Magnetic Intensity. 351 



bers of the thermometer, was placed at different distances 

 from it. The results deviated very considerably Jrom the law 

 of the squares of the distances. . 



Exp. % The same experiment was repeated with a canister 

 of a smaljer diameter. The results now approached more 

 nearly to the squares of the distances. 



Exp. 3. Iron balls about two inches in diameter were now 

 substituted in place of the canister. The results were now 

 within the limits of error, as the squares of the distances of 

 the centres of the balls from the end of the instrument. 



Exp. 4. Two heated balls were placed on one side of the 

 instrument, and one on the other, (the whole being of the same 

 temperature,) and the instrument was moved till the fluid re- 

 mained at zero. The distances of the centres of the balls were 

 then as 1 to the square root of 2. 



The deviation from this law in the case of the large canister 

 was ascribed by Mr Leslie either wholly or in part to imper- 

 fect reflection ; but as the same anomaly takes place without 

 reflection^ Mr Ritchie concludes that this cause cannot be the 

 true one. 



Art. XXXI. — Notice respecting Professor HansteerCs New 

 Chart of the Isodynamic Lines for the whole magjietic in- 

 tensity. With a Chart, Plate IV. Communicated bv 

 Professor Hansteen of Christiania. 



VY E have much pleasure in laying before our readers a cor- 

 rected chart (Plate IV.) of Professor Han steen's Isodynamical 

 lines for the whole magnetic intensity, which he has been so 

 kind as to communicate to us. It contains the recent obser- 

 vations made by Captain King at Rio Janeiro and Maldonado 

 Bay, near the River Plate. 



The dotted line of the dip in 1780 will be seen cutting the 

 equator in 90=^ west longitude, and passing through Bahia to- 

 wards the equator in 40° east long. The same line for 1823 

 will be seen to the south of Bahia, cutting the former in 10® 

 west longitude, and passing to the south of Ascension and St 

 Thomas. 



