1SI4.] Chromic Acid uutfi different Bases. 42J 



appear to be so easily decomposed as chromate of nickel ; for the 

 brown mass dissolves in water, except a small residue, which is a 

 mixture of oxide of chromium and oxide of uranium. The solu- 

 tion has a yellow colour, and potash precipitates from it yellow 

 oxide of uranium. 



Article V. 

 On the Aurora Borealis. By Thomas Thomson, M.D. F.R.S. 



There are few phenomena which have more attracted the 

 attention of the curious than the Aurora Borealis, and scarcely any 

 concerning the nature and origin of which we are more completely 

 ignorant. I conceive, therefore, that it will be attended with utility 

 to collect into one point of view the principal facts that have been 

 ascertained respecting it, and lay them in their naked simplicity be- 

 fore my philosophical readers : — 



1. This phenomenon was considered by the ancients as a preter- 

 natural appearance, which prognosticated some great event, or some 

 important change in the country over which it was visible. It was 

 usually described as armies of horse and foot engaged in battle in 

 the sky. In this way we find it mentioned as appearing before the 

 death of Julius Caesar, and it was universally considered as foretelling 

 that important event. For more than a year before the siege and 

 destruction of Jerusalem by Titus Vespasian, the Aurora Borealis 

 was very frequently visible in Palestine, and it is minutely described 

 by the historian Josephus as one of the most remarkable prognostics 

 of the disasters that were to follow. 



Even as late as the reign of Queen Elizabeth, during which this 

 phenomenon was not uncommon in England, it is described under 

 the denomination of burning spears, or some similar appellation 

 obviously alluding to the old opinion that it represented hostile 

 armies engaged in battle. They wen: seen at London on January 

 the 30th, 1560, and on the "Jth of October, [564. Camden and 

 Stowe inform us that they were seen on the 1 1th and 15th of Nov. 

 15/4. These, as far as i know, arc the only instances upon record 

 of their being observed in England during that period ; but several 

 foreign writers mention their appearance pretty much about the 

 same time. Thus Cornelius Gemma, Professor of Medicine in 

 Louvaio, mentions them under the name of cfiasma, as appealing 

 in Brabant on the 13th February and 28th September, lf>75. 

 Michael Msastlin, celebrated as the tutor of Kepler, informs us that 

 during the year 1580 he saw these cfuumata, as he culls them, 

 twelve different times in the course of one year, at Baknang, in the 

 country of YYirtcmberg. 



Caisendi describes a phenomenon of the same kind which was 



