<< geedful to prefere the material Syftem. 2rg 
phere, and is the atmofphere itfelf, or its vapour. It is appre- 
hended, however, that this would be a miftaken fuppofition ; 
and that the appearance may be explained on principles, which 
will not only invalidate the fuppofition, but further (hew the 
infafliciency of the caufe, to which the phenomenon has, been 
afcribed. . 
-For that purpofe it may. be iraa that the EES E 
being invifible, muft be without colour ; and has, perhaps for 
that reafon, no greater difpofition to tranfmit or refle& to us 
the’blue rays of light, whether of the fun or ftars, than thofe 
of the.other. colours : and; therefore, if. the phenomenon be 
produced by means of the blue rays of thofe luminaries (which 
I (hill attempt to explain) the amolar cannot be. pees 
of that produétion.:! "bsp 
With refpet othe ‘vapours in — which, ina - 
particular ftate, are faid to oceafion the phenomenon, they be- 
ing of different degrees of groffne(s- or. denfity, mutt arrange 
themfelves: according to: that denfity, or their fpecific gravity. 
If. then any of the ranges. confifted of vapour, in a proper ftate 
to tranfmit or gene to the eye the bbe ras only, the effect of 
uld be deftfoyed, or changed, by. er vapour inthe 
lower range. | Okifit Mould i5 de {which Tees very im- 
probable) that the whole body of vapour fhould confit of par- 
titles ofthe: due fize, and in the proper ftate, to reflect the: blue 
rays, it could not long continue i in that-ftate, by reafon of the 
changeable — of the’ i seal and the numerous ane 
that are-con intly operating to produce a change i init." But 
enon is. uniform and premanent ; and thereforemuft — 
be’ the eRe ofan Bises and Papam Cuníe, s jet 2 
"Pu 
