Intelligence and Miscellaneous Articles. 159 



of-ammonium solution contained 1'13 grm. of the dry salt. Hence 

 1 part of sulphate of lead was held dissolved for every 4*6617 parts 

 of the dicitrate. 



Tricitrate of Potassium. — 25 cubic centims. of a standard solution 

 of ordinary crystallized citrate of potassium mixed with an equal 

 volume of the standard sulphuric acid gave no permanent precipitate 

 until 2 cubic centims. of the solution of acetate of lead had been 

 added to it. 



Sugar. — A standard solution of cane-sugar mixed with an equal 

 volume of the sulphuric acid gave a permanent precipitate on the ad- 

 dition of the first drop of the acetate of lead. 



These experiments show clearly that very considerable quantities 

 of sulphate of lead can be held in solution by weak alcohol charged 

 with various salts. It may therefore reasonably be inferred that 

 wines sometimes retain lead in solution in consequence of this action 

 of the acids and salts peculiar to wine upon lead compounds igno- 

 rantly employed to correct acidity. — Communicated by the Author, 

 from Proceedings of the American Academy of Arts and Sciences, No- 

 vember 11, 1868. 



ON AURORAL APPEARANCES AND THEIR CONNEXION WITH THE 

 PHENOMENA OF TERRESTRIAL MAGNETISM. BY BALEOUR 

 STEWART, E.R.S., E.R.A.S. 



Some years since, I ventured to suggest that auroral displays 

 might be secondary currents due to small but rapid changes, caused 

 by some unknown influence, in the magnetism of the earth. In de- 

 veloping this idea, the earth was compared to the core of a Ruhm- 

 korff machine, and the moist upper strata of the earth, as well as the 

 upper strata of the atmosphere, to secondary conductors, in which 

 currents will take place whenever the magnetism of the earth changes 

 from any cause. These views would appear to be confirmed by the 

 very interesting records of earth-currents obtained by Mr. Airy at 

 the Greenwich Observatory, in which it is found that during times 

 of very great magnetic disturbance there are strong earth-currents 

 alternating from positive to negative, the curves lying nearly equally 

 on both sides of the zero. 



A further development of this idea has lately occurred to me, in 

 consequence of a remark of my friend Mr. Lockyer, that the zodiacal 

 light may possibly be a terrestrial phenomenon, and may therefore 

 be somehow connected with the phenomena of terrestrial magnetism. 

 For not only will secondary currents be caused in a stationary con- 

 ductor in presence of a magnetic core of variable power, but also in 

 a conductor moving across the lines of force of a constant magnet. 

 The question arises, have we on the earth such moving conductors ? 

 In answer to this, let us reflect what takes place at the equator. 

 When once the anti-trades have reached the upper regions of the 

 atmosphere, they will become conductors from their tenuity ; and as 



