170 Scientific Intelligence 



in ike direction of their length ; whereas in the lattery it is in the direction of 

 their breadth, particularly when a single bar magnet is used, — Le Globe, 

 September 20th 1827. 



ELECTRO-MAGNETISM. 



9. On the rotation of a magnet about its axis. — M. Pouillet has succeeded 

 in giving a magnet a motion of rotation by means of a metallic ring nearly 

 encircling the magnet, which must be nearly cylindrical, and by placing 

 on the ring a small quantity of mercury in contact with the magnet, and 

 which the capillary force prevents from escaping out of the small inter- 

 val which is left between the magnet and the ring. 



By this means, the communication being made between one of the ends 

 of the pile and the magnet, as in Ampere's apparatus, by a small cavity 

 full of mercury hollowed in the upper end of the magnet, the communi- 

 cation with the other end of the pile takes place only at the points of the 

 horizontal section of the needle or the point where the ring is placed. By 

 this arrangement we may compare the velocities of rotation which corre- 

 spond to each position of the ring along tlie magnet. M. Pouillet has shown 

 that the velocity is a maximum when the ring is placed at the middle of 

 the magnet ; that it goes on diminishing, but remains always in the same 

 direction whether the ring rises or falls ; and that the magnet remains im- 

 moveable when the ring is placed very near one of its extremities beyond 

 the pole.— ie Globe, Aug. 28, 1827. 



METEOROLOGY. 



10. Sound of the Aurora Borealis in Iceland, observed by Mr Henderson."^ 

 *' The most striking aerial phenomenon exhibited by an Icelandic winter 

 is doubtless the Aurora Borealis or Northern Lights, which are here seen in 

 all their brilliancy and grandeur. I had an opportunity of contemplating 

 them almost every clear night the whole winter, sometimes shoothig across 

 the hemisphere in a straight line, and presenting to the view, for a whole 

 evening, one vast steady stream of light; but more commonly they kept 

 dancing and running about with amazing velocity, and a tremulous motion 

 exhibiting as they advanced some of the most unrivalled appearances. On 

 gaining one point of the hemisphere, they generally collected as if to mus- 

 ter their forces, and then began again to branch out into numerous ranks, 

 which struck off to the greatest distance from each other as they passed 

 the zenith, yet so as always to preserve the whole of the phenomenon in 

 an oval shape ; when they contracted nearly in the same way as they ex- 

 panded, and after uniting in a common point, they either returned in the 

 course of a few minutes, or were lost in a stream of light, which grew 

 fainter and fainter the nearer it approached the opposite side of the heavens. 

 They were mostly of a dimmish yellow, yet often assuming mixtures of red 

 and green. When they are particularly quick and vivid, a crackling noise 

 is heard, resembling that which accompanies the escape of the sparks from 

 the electrical machine. They almost always took their rise from the sum- 

 mit of Mount Esian, which is about due north-east from lieykiavick, 

 and proceeded to a south-west direction. When visible the whole length 



k 



