M. Martins and Spix's excursion to the Diamond^ <§*c. 241 



sheet.) Then join together by means of a galvanometer wire 

 the plate of zinc with that of copper, and you will obtain a 

 deviation of a few degrees. Plunge then the plate of copper in 

 the glass which contains the tail or band, and the plate of zinc 

 in the other glass, and the effect will be much more striking. 



It would be in vain to en4eavour to explain this fact by 

 the help of the theory of two fluids, since if, on the one hand, 

 when the plate of zinc is put into the glass which holds 

 the band, the passage is difficult to the vitreous fluid ; on the 

 other hand, when the copper replaces the zinc, and the latter 

 the copper, the passage is made difficult to the resinous elec- 

 tricity, and easy to the vitreous electricity. There is then no 

 reason why the effects are different. But in admitting the 

 theory of a single fluid, we know how, in the first case, the 

 electric fluid which expands itself by radiation in the liquid finds 

 the passage much more difficult than in the second instance ; 

 from which it appears, that the electro-magnetic effect, which, 

 as is well known, principally depends upon the rapidity of the 

 electric current, ought to be less in the first case, and greater 

 in the second. — (Ann. de Chimie.) 



Art IX. — Accotmt of an Excursion to the Diamond district in 

 the go'oernments of Bahia and Minas Gheraes in Brazil. * 

 By MM. Martius and Spix. 



1 HE district of diamonds is a kind of sanctuary into which it 

 is very difficult to penetrate. It is surrounded with a cordon of 

 dragoons placed in picquets at from five to six miles from each 

 other, who prohibit any person either from entering or leaving 

 the district, without the special authority of the intendant-gene- 

 ral of the province who resides at Tejuco. In quitting the dis- 

 trict, every person, whether a native or a foreigner, is searched 

 in the most rigorous manner. Not only are his baggage and his 

 clothes rigorously examined, but his person, as well as his horse 

 or his mules. The dragoons are also authorized to detain tra- 



* From M. Spix and Martius's Travels in Brazil, undertaken in 1817 

 — 1820, by order of the king of Bavaria, Maximilian Joseph I. torn. ii. 

 Munich, 1828. 



