hitelUgence mid Miscellaneous Articles. 4-69 



It is known that it does not occur at places situated in correspond- 

 ing latitudes north of the geographical equator ; at Algiers, for ex- 

 ample, — which is moreover nearly in the same geographical meridian 

 as the Cape, and where the magnetic inclination is nearly the same 

 towards the north as i& the case at the Cape towards the south. It 

 may be quite correct perhaps to view the corresponding phenomena 

 at St. Helena and the Cape as those belonging to magnetically -nc^^- 

 torial stations ; but they are certainly not those peculiar to or cha- 

 racteristic of geographically -Q(\Vi9.tox'wX stations, which would be the 

 condition in M. De la Rive's theory. There are thus two parts in 

 the problem demanding physical explanation ; on the one hand, 

 the cause is required of the contrariety of movement, as well as of 

 the times at which the different movements occur, the latter having 

 obviously a dependence on the sun's position either in the northern 

 or the southern signs ; and on the other hand, the cause must be 

 shown why certain stations are thus aiFected and others not : a di- 

 stinction which obviously does not depend on situation in regard to 

 the geographical equator or to the tropical divisions of the globe. 



I have myself been led to infer that the peculiarity in question re- 

 sults from and is indicative of proximity to the line of least mag- 

 netic force, regarded as physically the separating line on the surface 

 of the globe between the northern and southern magnetic hemi- 

 spheres ; the peculiarity would thus be strictly a magnetically- equa- 

 torial one. 



It results from the present position of the four points of maximum 

 intensity at the surface of the earth, that the intermediate line of 

 least intensity departs considerably in the Southern Atlantic from 

 the middle or geographically-equatorial portion of the globe, passing 

 between the Cape and St. Helena, and consequently not far from 

 either of these stations. 



As far as I have yet been able to examine, I have found that the 

 same remarkable peculiarity does exist at all other stations which 

 are near this line, and at none which are remote from it. But 

 however this may be, the accordance of the phenomena at the Cape 

 of Good Hope and St. Helena, and their dissimilarity from those at 

 other stations is a well-ascertained fact, of far too much bearing and 

 importance to be passed without notice ; and we may safely anti- 

 cipate that its cause must occupy a prominent place in the theory 

 which shall be ultimately received, as affording an adequate solution 

 of the problem of the diurnal variation. 



Believe me, my dear Sir, sincerely yours, 



Edward Sabine. 

 S. H. Christie, Esq., Secretary to the Royal Society. 



LXX. Intelligence and Miscellaneous Articles. 



ON SOME METEOROLOGICAL PHENOMENA. 



BY PROF. E. WARTMANN. 



f\N a mirage with a strong bise. — Most of the mirages described 



by authors appear to be manifested in a tranquil state of the air. 



M. Kamtz even affirms that a calm atmosphere is indispensable to their 



