324 Intelligence and Miscellaneous Articles. 



cess would be in a great measure arrested, and an effect would be 

 produced similar to that of a screen of glass, which keeps up the 

 temperature beneath it, directly by preventing the escape of radiant 

 heat, and indirectly by hindering the condensation of the aqueous 

 vapour in the air confined beneath. 



Now we have only to bear in mind that there are the best of 

 reasons for believing that, during the earlier geological periods, all 

 of the carbon since deposited in the forms of limestone and of mine- 

 ral coal existed in the atmosphere in the state of carbonic acid, and 

 we see at once an agency which must have aided greatly to produce 

 the elevated temperature that prevailed at the earth's surface in for- 

 mer geological periods. Without doubt the great extent of sea, and 

 the absence or rarity of high mountains, contributed much towards 

 the mild climate of the carboniferous age (for example) when a vege- 

 tation as luxuriant as that now found in the tropics flourished within 

 the frigid zones ; but to these causes must be added the influence of 

 the whole of the carbon which was afterwards condensed in the form 

 of coal and carbonate of lime, and which then existed in the condi- 

 tion of a transparent and permanent gas, mingled with the atmo- 

 sphere, surrounding the earth, and protecting it like a dome of glass. 

 To this effect of carbonic acid it is possible that other gases may 

 have contributed. The ozone, which is mingled with the oxygen set 

 free from growing plants, and the marsh-gas, which is now evolved 

 from decomposing vegetation under conditions similar to those then 

 presented by the coal-fields, may by their great absorptive power 

 have very well aided to maintain at the earth's surface that high 

 temperature the cause of which has been one of the enigmas of 

 geology. 



Montreal, August 1, 1863. 



ON SOME PHENOMENA PRODUCED BY THE REFRACTIVE POWER 

 OF THE EYE. BY A. CLAUDET, F.R.S.* 



One of the most beautiful and extraordinary results of the struc- 

 ture of the human eye is the considerable field of vision it embraces. 

 The external objects which are represented on the retina are included 

 Jn an angle much larger than one-half of the sphere at the centre of 

 which the observer is placed ; and from this point of view a single 

 glance encompasses a vast and splendid panorama, extending in a 

 horizontal and vertical direction to an angle of 200°. 



If we lie on the ground, we see the whole vault of the sky, and 

 10° all round lower than the horizon. In that position, having our 

 face directed to the zenith, if, at the time of opposition, the moon 

 was just rising in the east, and the sun setting in the west, we could 

 see simultaneously the moon with one eye and the sun with the 

 other; and, although both forming actually an angle of 180°, they 

 would appear to form one only of 160°. 



* Communicated by the Author, having been read at the British Asso- 

 ciation Meeting, Newcastle-upon-Tyne, August 27, 1863. 



