^Q Intelligence and Miscellaneous Articles. 



this is what we have done in calculating the table relating to »=4, 

 1=5, up to 2=11, which is sufficient for all possible cases. 

 As the formula r / l \ -«' "I 



is not exact, we have endeavoured to make the necessary correction 

 to ^1, so that on consulting our tables, we may come at once upon 

 the exact value of n, and we have found 



A^=-,o_^^2+i). 



^0 = 



_ 9o_ Jio_ 



a— I 



The coefficient /io is obtained by an observation made simultaneously 

 with the repeating and ordinary barometers. We have calculated a 

 small table giving this correction A/i. 



The accuracy of the repeating barometer to that of the ordinary 

 barometer is in the proportion oi q to n; taking a = 0"450 M, 

 /=0-070M; this exactitude at the level of the sea is nearly as 1 

 is to 1 ; that is to say, that 1 millimetre of variation of the ordinary 

 barometer corresponds with about \ a millimetre of that of the re- 

 peating barometer. But this exactitude increases in proportion as 

 we rise, because then n diminishes, and at an elevation of 2000 to 

 3000 metres the two exactitudes are nearly equal. 



In a numerous series of observations made with the two barome- 

 ters, the disagreement rarely rose to 1 millim. ; most frequently it 

 was limited to a few tenths of a miUim. more or less. 



Up to a certain point the observations may be verified by making 

 them with two consecutive values of i, which ought to give nearly 

 the same value for n. 



I must not omit to mention that my formulse suppose the tube to 

 be perfectly cylindrical, which is very rarely the case, but from their 

 construction the tubes alFect a slightly conical form. To remedy 

 this inconvenience, I show that with a sufficient approximation it 

 suffices to make the obser\'ations twice, keeping each extremity of 

 the tube successively in the £iir, and taking the average of the values 

 thus observed of q h 



m a— I 

 —Comptes Rendus, March 30, 1857, p. 658. 



ON A NEW LOCALITY FOR THE MINERAL ATACAMITE. 

 BY J. J. MOXTEIRO. 



This mineral (CuCl + 3CuO HO) occurs abundantly crystallized 

 on malachite, massive quartz and gozzan, obtained from the extra- 

 ordinary deposit of malachite in the Serra do Bembe near Ambriz, 

 on the west coast of Africa. It occurs in small, distinct, rhombic 

 prisms, translucent, and of a hght to opake and dark green colour 

 with vitreous lustre ; the symbols, for the crystals being, according 

 to Naumann's system, = cc P . Px . 



The probable existence of this mineral in considerable quantity at 

 the above locahty, as at Atacama and other parts of Chili, remains 

 to be yet ascertained. 



