OF THE COSMOS. NUMBER OP THE FIXED STAHS. 87 



ally during the day-time it is possible to distinguish the 

 outline of the Sun's disk, it appears rayless ; shorn of its 

 beams, as if viewed through a coloured glass ; usually of a 

 yellowish red or orange colour ; now and then white, or most 

 rarely bluish green. Navigators, driven by the cold oceanic 

 current flowing from south to north, and unable to obtain 

 observations for latitude, sail past the harbour which they 

 desire to enter. It is only, as I have shown elsewhere, 

 by the use of the dipping needle ( 168 ) that, thanks to the 

 direction of the magnetic lines in that part of the globe, 

 they may be enabled to avoid error. 



Bouguer and his coadjutor, Don Jorge Juan, complained 

 long before me of the " uuastronomical sky of Peru." A 

 grave consideration is suggested by the character of this atmo- 

 spheric stratum, which is so unfavourable to the transmission 

 of light, and so unfitted for electric discharges, that thunder 

 and lightning are unknown there, and which veils the 

 plains in constant mist, while above, the Cordilleras raise 

 aloft, free and unclouded, their elevated plains and snowy 

 summits. According to the conjectures which modern 

 geology leads us to form respecting the ancient history 

 of our atmosphere, its primitive state, in respect to com- 

 position and density, must have been but little favour- 

 able to the passage of light. If, then, we think of the many 

 processes which may have been in operation in the early 

 state of the crust of the globe, in the separation of solid, liquid, 

 and gaseous substances, we are impressed with a view of how 

 possible it must have been, that we should have been subjected 

 to conditions and circumstances very different from those 

 which we actually enjoy. We might have been sur- 

 rounded by an untransparent atmosphere, which, while but 



