312 Mr G. A. Rowell on the 



Virginian. — (For an account of Professor Forbes's regions of 

 depths, vide vols. 50, 51, and 52, Edin. New Phil. Journal ) 



On the Change of Temperature in Europe, and the Variation 

 of the Magnetic Needle. By Mr G. A. Ro;vell.* With 

 a Map. 



From the attention now given to the effects of glaciers in 

 producing geological phenomena, much interest has been 

 excited as to the cause which has brought about the change 

 of temperature in Europe since the glacial period. 



This change of temperature is, I believe, intimately con- 

 nected with the change of declination of the needle, and in 

 the theory which I first submitted to this Society in 1839, 

 on the cause of terrestrial magnetism, I attributed the 

 change of declination in this hemisphere to a decrease of 

 temperature in the higher latitudes of America, or to an in- 

 crease of temperature in those of Europe and Asia. In a 

 recent communication on Scandinavia, allusion has been made 

 to several geological facts, which are, I believe, connected 

 with the cause of these changes. I trust, therefore, I have 

 chosen a proper time to bring the subject under the consi- 

 deration of this Society, as I hope to shew the causes of this 

 change of temperature, and also the probability that these 

 causes have been in operation to a sufficiently recent time, 

 to account for the variation of the needle. 



Before I proceed further, I will describe the accompany- 

 ing Map, as I shall have to refer to it often. 



The lines of equal magnetic intensity are shewn by the 

 broken lines ; these are taken from Col. Sabine's maps, in 

 the Sixth Report of the British Association. The point of 

 greatest intensity is shewn by the spot at 52° 19' north lati- 

 tude, 92° west longitude ; the intensity decreasing from this 

 point as shewn by the lines 1.7 — 1.6 — 1.5 — 1.4 The 

 American magnetic pole, according to Sir James Ross, is in 

 north latitude 70° 51', west longitude 96° 4C. The Asiatic 

 magnetic pole, according to Hansteen's observations, is in 



! before the Ashmolean Society, January .'31, 1853. 



