1 8 3 Misccllan ics. 



distance, and in situations where no clouds appear* To regard these 

 flashes as arising from electrical discharges in an air in which there is 

 no condensation of vapor in the form of cloud, he pronounces to be 

 unphilosophical, and maintains that if electricity becomes thus visi- 

 ble, the phenomena should sometimes be seen in or near the zenith, 

 whereas it is always observed near the horizon. A person situated 

 on the summit of a high mountain, while a thunder storm is raging 

 beneath him, at so great a distance as scarcely to be heard, he sup- 

 poses to be in a position analogous to the spectator of the noiseless 

 flashes of a summer evening. 



The editors of the Bib. Univ. dissent from these views of Huber- 

 Burnaud. The fact that these lightnings are sometimes seen all 

 around the horizon proves, in their opinion, that they cannot be at- 

 tributed to distant thunder storms ; and although it is rare that these 

 heat lightnings are seen in the zenith, yet there have been instances 

 of their appearance over the head of the observer. The produc- 

 tion of electric light requires only a rarefied state of the atmosphere, 

 either by the effect of heat or by the presence of aqueous vapors. 

 Such an atmosphere becomes a conductor, through which the dis- 

 charges become visible from one portion of the air to another, and 

 in such gentle streams as to afford light without noise. — Bib. Univ. 

 JYov. 1829, 



10. Determination of metallkity . — The simple and ingenious 

 method which Dr. Wollaston employed to discover metallic titanium 

 in the scoria of iron, and to prove the metallicity of the small crys- 

 tals of titanium, was to place a card or slip of paper between a plate 

 of zinc and another of copper, make a small hole in the card, into 

 which he inserted the crystal to be examined, and then plunged the 

 apparatus into diluted acid. If the substance placed in this opening 

 is a metal, bubbles of hydrogen will be disengaged ; but if not me- 

 tallic, this effect is not produced. The paper disk prevents the elec- 

 tric action of the two surfaces, and nothing but a conductor of the 

 most perfect kind, thus inserted between them, in the small opening, 

 will establish it. Thus lead, bismuth, tin, give bubbles on the cop- 

 per; while the oxide of titanium, sulphuret of arsenic, gray cobalt, 

 sulphuret of antimony, iron pyrites, galena, tin ore, &c. have no ef- 

 fect. Two specimens of meteoric stone, introduced into the circuit, 

 showed, by bubbles of hydrogen, the presence of uncombined metal, 

 and it has been found, by the ingenious experiments of Macaire- 



