120 ANNUAL OF SCIENTIFIC DISCOVERY. 



the rotation begins, and the jet not only expands into an arc, but 

 darts brilliant rays that remain quite distinct from each other, and 

 turn round with greater or less velocity like the spokes of a wheel. 

 In this we see an exact representation of what occurs in the aurora 

 borealis, when the luminous arcs, being all impressed with a move- 

 ment of rotation from west to east, dart luminous jets in the higher 

 regions of the atmosphere. These jets do not occur unless the iron is 

 magnetized, and they may be stopped if the air is highly rarefied by 

 introducing a vaporizable liquid, such as a drop of water. It is im- 

 possible to produce them if the discharge, instead of being directed, 

 as in nature, from the circumference to the centre, passes in an oppo- 

 site direction." 



M. de la Rive adds, that on examining the galvanometer with 

 which the two wires previously mentioned are in communication, a 

 secondary current will be indicated, its character and direction being 

 determined by whether the discharge takes place at one pole or the 

 other ; and he states that he can imitate the disturbances which the 

 magnetic needle experiences when the auroras occur. Comptes 

 Rendus. 



SECCHI ON MAGNETIC AND ATMOSPHERIC PERTURBATIONS. 



In a recent letter to the French Academy, the distinguished Ro- 

 man astronomer gives a summary of the conclusions he has arrived 

 at respecting the connection between magnetic perturbations and 

 atmospheric movements. This he considers established, first, by the 

 great variations of magnetic elements, and especially in the intensity 

 of the horizontal force, on the occurrence of storms ; secondly, by the 

 irregularities which accompany periods of squalls; thirdly, by the 

 variations in delicate magnetic instruments which immediately pre- 

 cede or follow great changes in the weather ; fourthly, by variations of 

 intensity corresponding with variations of the winds ; fifthly, by the 

 aurora borealis, which, considered as a signal of variation in wind 

 and weather, belongs to the class of phenomena under discussion. 



The immediate cause of the connection thus traced M. Seeehi as- 

 cribes to atmospheric electricity, which, when discharged from the air 

 to the earth, must generate strong currents by which the needle is 

 affected. Such currents, he observes, exist not only during auroral 

 manifestations, but also during storms, and are exhibited by each 

 instrument according to its nature, the galvanometer showing changes 

 in tension, and the compass-needle making known alterations in the 

 total force of the current which passes beneath it. With reference 

 to the questions of whence comes the electricity circulating in the 

 soil, and what is its immediate vehicle, he replies by pointing to the 

 precipitations from the atmosphere. The rain especially, he says, 

 discharges an immense quantity of electricity into the earth, and, in 

 general, it may be said that strong actions upon the instruments only 

 occur after a rainfall has taken place at some point more or less 

 remote, even beyond the limits of the visible horizon. This circum- 

 stance may, perhaps, explain the fact that magnetic perturbations 

 indicate approaching squalls. Rain usually produces negative elec- 

 tricity over a considerable extent of atmosphere, and it is itself gen- 



