Chemical Science. 229 



of the motion in the disc, the motion of the spiral immediately 

 chan^red, in all cases continuine: the same as that of the plate. This 

 satisfactory fact is a powerful addition to those by which M. Ampere 

 supports his views of the natureof magnetism generally, and its ori- 

 gin in all cases from currents of electricity. — Bull. Phi. 1826, p. 134. 



3. Influence of the Aurora Borealis on the Magnetic Needle. — A 

 luminous arc produced by an aurora borealis was seen on the 29th 

 of April, 1826, at Carlisle and in Roxburghshire. This phenome- 

 non was not seen at Gosport, though the sky was very clear. At 

 7 h. 50' P.M. of the 29th April at Paris, the north point of the needle 

 indicating diurnal variations was 4 to the east of its ordinary posi- 

 tion ; at half past eight o'clock it passed westward with a ready 

 movement ; at three-quarters past eleven o'clock it had returned 

 within half a minute to the position it had at half-past eight. Long 

 experience has taught me that these great oscillations, at hours 

 when the needle is generally stationary, is an indication almost cer- 

 tain of the existence of an aurora borealis. M. Arago, the author 

 of these observations, then ventures to announce, solely from the 

 effects he has observed upon the magnetic needle, that brilliant 

 aurora boreales will have been observed in some part in the north 

 on the following days of the year 1826 : the 16th of January, the 

 10th and 13th of February, the day of the 9th of March, the morn- 

 ing and evening of the 23rd of March, and the 29th of the same 

 month, the 9th and 13th of April, the nights of the 17th and 18th 

 of April, the 24th of the same month, &c. — Annales de Chimie, 

 xxxiii. 421. 



4. Electro-chemical Appearances. — M. Nobili has been induced 

 to contract one of the poles of the voltaic pile in the manner first 

 pointed out by Dr. Wollaston, namely, by inclosing a wire within 

 a glass tube, and exposing only a sectional surface, and has ob- 

 served the effects which occur when such a pole is used in the de- 

 composition of various saline solutions, the other pole being a plate 

 of metal, brought very near to it. The general results appear to 

 be two in immber. The first consists in the property remarked of 

 certain electro-negative substances to attach themselves, in cer- 

 tain determinate circumstances, to the surface of those metals 

 which are least oxidable, in thin regular layers, so as to present the 

 beautiful phenomenon of coloured rings in a splendid manner. This 

 effect, it is supposed, may be applicable in the ornamental arts. 

 The second is, that when electro-negative substances are not depo- 

 sited in thin plates upon the metals, they generally attack their 

 surfaces, not in an uniform manner, as might be supposed, but by a 

 gradation of intensity from the centre, continued and decreasing, but 

 at irregular intervals, following, as it were, a law analogous to that 

 of interferences. The same phenomenon is observed in the attach- 

 ment of electro-positive substances to the negative pole, namely, an 

 alternation in the circles of oxide and of metal. M, Nobili then 



