356 Mr Christie on the Tlteori^ of the 



suffer dividing at the root; but he was determined it should 

 support the specific name he had conferred on it. It appears 

 to be a TiUandsia from South America : the flowers are blue, 

 and it is probably a described species. No chmate in Europe 

 is more healthy, and more equal than that of Barcelona ; none so 

 well adapted for the establishment of a botanic garden on a grand 

 scale, if the government of that unfortunate and degraded coun- 

 try were of a nature to permit a distinguished botanist to exer- 

 cise there his talents, or had sufficient liberality to give him the 

 necessary funds for such a purpose. 



(To be continued.) 



On the Theory of the Diurnal Variation of the Needle. By S. 

 H. Christie, Esq. F. R. S.* 



jSjLVi Christie having been led to doubt the validity of the 

 moving easterly variation adopted by Canton, but, at the same 

 time, having observed that the changes in direction and inten- 

 sity appear always to have reference to the position of tlie sun, 

 with regard to the magnetic meridian, was led to connect these 

 phenomena with Professor Seebeck''s discovery of thermo-mag- 

 netism, and Professor Cumming's subsequent experiments ; and 

 to refer the phenomena of diurnal variation to the effect of par- 

 tial heating, modified, perhaps, by- that of rotation, and by pe- 

 culiar influence in the sun''s rays. 



In support of this opinion, he cites passages from papers by 

 Professor Cumming and Dr Trail, who appear to have been 

 impressed with a similar idea. But in place of looking to the 

 stony strata of which the earth's surface consists, as the elements 

 of the thermo-magnetic apparatus which this doctrine requires, the 

 author regards them as rather consisting of th^ atmosphere, and 

 the surfaces of land and water with which it is in contact. 

 Thermo-magnetic phenomena, he remarks, have hitherto only 

 been observed -in metallic combinations; but this may be owing 

 merely to the small scale on which our experiments are con- 

 ducted. 



• The above is a brief account of an interesting memoir read lately before 

 the Royal Society of London. 



