170 METEOROLOGICAL PERIODTCITT. 



throw light on many historical statements^ and phenomena that 

 have been observed in more recent times — phenomena which I 

 I think a little consideration will convince us could not take place 

 without producing very decided effects upon the earth's atmo- 

 sphere. 



It has been proved that the number of meteor streams is 

 almost inconceivable ; that they revolve about the sun at all 

 degrees of inclination to the ecliptic, and in all sorts of periods ; 

 that many of them have their perihelion within the earth's orbit ; 

 and that in the meteor rings there is not a uniform distribution 

 of the matter composing it, as has been shown by Professor 

 Newton. AVith regard to comets also, facts seem to prove that 

 they are not uniformly distributed in sj)ace, the sun in his onward 

 course meeting more at one time than at another. "From IGOO to 

 1750 (150 years), only sixteen comets were visible to the naked 

 eye ; of these, eight appeared in twenty -five years (1664 to 1689) ; 

 and during the sixty years (1750 to 1810) only five comets were 

 visible to the naked eye, while in the next fifty years there were 

 double that number." — (" Kirkwood.") 



Erom these known conditions we sliould expect that at times 

 the earth would pass regions of greater meteoric density, in 

 which the denser portions of meteor rings happened to come 

 together ; in this way, in all probability, so much matter inter- 

 venes between the earth and sun that his heating power is tem- 

 porarily much reduced.* And every one who has watched the 

 sun's heating power knows that it varies enormously, and the 

 sun-spots do not seem to affect it. "When these changes are 

 observed in the solar radiation, all that can be seen with the 

 telescope directed to the sun is a troublesome thickness and con- 

 fusion in the air that is a bar to all delicate observations. At 

 night the same thickness in the air may often be detected, and it 

 reveals itself to the naked eye as a phosphorescent or milky 

 a^^i^earance in vvhat should otherwise be a black sky. 



It is amongst these phenomena, the laws of which are daily 



* And observation proves this to be fact, for whenever the sun has been 

 seen in total eclipses its envelope has had a most irregular form, generally- 

 radiated. At times the corona, as in December, 1870, extended round 180^ 

 of the sun's circumference, while the other 180° was divided into three 

 irregular rays by dark spaces which extended nearly to the sun's limb ; or 

 again, as in 1868, forming no less than nine rays extending from the sun to 

 an immense distance into space. In 1870, photography proved that the corona 

 extended for nearly double the sun's diameter on one side, while at another 

 place the extent Mas only one-eighth of this, and it is evident that matter 

 which is capable of reflecting light and heat must be also sufficient to 

 prevent some of the radiation from the sun, and, as Proctor justly remarks, 

 "Science By-ways," page 161, "no reasonable doubt can exist that the 

 matter (forming the solar corona) is no other than the meteoric and 

 cometic matter which other researches have taught us to recognise as plen- 

 tifully strewn throughout the regions around the sun." 



