Electro-Mag netism — Meteorology. 369 



in June 1824, to be 26° SO' west. Bywell is in lat. 55° 1' north, and long, 

 1° 59' west. 



17. Magnetic Declination near St Petersburg in 1824. — The magnetic 

 declination near St Petersburg, in lat. 59° 58' 31" north, and long. 30° 

 19' 45" east, was found, by the late Professor Schubert, to be 7° 36'. 



ELECTRO-MAGNETISM. 



18. On the Magnetising of Needles by Currents and Electric Sparks.— 

 On the 31st July last, M. Savary communicated to the Academy of Scien- 

 ces a highly important memoir on magnetisingjieedles by currents and elec- 

 tric sparks. The following are the leading points of this great discovery : 



1. The direction of the magnetic polarity of small needles, exposed to an 

 electric current, directed along a wire stretched longitudinally, varies with 

 the distance of the wire. 



2. This action is periodical ; — that is, when the small steel needle, which 

 is in relation with the wire, is magnetised in a certain direction, at a cer- 

 tain distance, the magnetism diminishes as the needle is removed, till at a 

 certain distance it becomes nothing. At a greater distance it recovers its 

 magnetism, but in a contrary direction, and it goes on increasing till it 

 reaches its maximum at a particular distance. It then diminishes as the 

 removal of the needle is continued, and again becomes nothing. The 

 magnetism then resumes its first direction, which constitutes a new period. 

 M. Savary has observed three periods. 



3. The distances at which the zero and the maximum of magnetism 

 take place vary with the length and diameter of the wire, and with the in- 

 tensity of the discharge. 



4. When a helix is used for magnetising, the distance at which the needle 

 placed within it is from the conducting wire is indifferent, but the direction 

 and the degree of the magnetism depends on the intensity of the discharge, 

 and on the ratio between the length and size of the wire. 



5. The maximum of intensity, which can be produced with a given wire, 

 depends on the ratio between its size and length, so that it is only for a 

 certain value of this ratio that we can obtain the degree of magnetism cal- 

 led the state of saturation. For all other ratios the maximum is less. 



6. Any metal placed in the vicinity of the needle has a very powerful 

 influence on the direction and degree of the magnetism. 



7. These effects vary with the relative positions of the wire, the needle, 

 and the metal. 



8. The direction of the action of the metal depends on the intensity of 

 the discharge, so that discharges different in intensity, develope in the me- 

 tal a series of opposite states, analogous to the polarities of opposite signs, 

 which small needles acquire at different distances from the conducting wire, 

 or for different intensities of electricity. — Le Globe, No. 96, August 2, 

 1826. 



METEOROLOGY. 



19. Meteorological Observations made on the 11th of July hist. — Ota 

 meteorological readers will be gratified to learn, that many of the meteoro- 



