95 THE SUN PROBABLY A PERIODIC STAR. 



trine of diminution of terrestrial temperature ; a doctrine which is enforced by argu- 

 ments furnished as well by the inorganic world. 



382. But radiant heat is not the primitive force which organizes the carbon atoms, 

 and groups them into their various forms ; it acts a subsidiary part, the decomposition 

 and subsequent arrangement being directed by LIGHT. Whatever facts, therefore, ex- 

 ist, which prove an increased activity in vegetable growth in the early times, prove also 

 an increased brilliancy in the light. The occurrence of an excess of carbonic acid in 

 the air, or of a higher temperature, is not enough. To the light, which is the vital 

 agent, a greater activity must be assigned. It is thus we perceive that changes in the 

 interior temperature of the globe can have had only an indirect connexion with what 

 was thus going on on its surface. And if there have been periodic vicissitudes, if plants 

 have once grown with excessive luxuriance, and in short spaces of time withdrawn 

 large quantities of carbon from the air, this is a result which is connected not so much 

 with internal or external temperature as with periodic variations in the brilliancy of 

 light. 



383. Do not, therefore, these things seem to indicate that our sun is one of those 

 periodic stars, the light of which undergoes secular changes ; that for a series of years 

 or of centuries it increases in brilliancy, and then fades away ; and that, as these peri- 

 ods pass over, corresponding mutations in its intensity of radiation are observed ? That, 

 affected by this, the rate of vegetable growth, the character of animal life, the constitu- 

 tion of the atmosphere is simultaneously changed in all the attendant planets ? It is 

 of no consequence to say that great and almost universal mutations, such as those we 

 are here describing, are not consonant to the ways of Nature ; or that, in the periods 

 of human history, traces of such operations have never been witnessed. No observa- 

 tion in philosophy is more true, than that " changes which are rare in time become 

 frequent in eternity." 



384. But among the stars these periodic variations do take place. As was discov- 

 ered by Sir J. HERSCHEL, a Orioni*, if examined, is seen to increase in brilliancy for 

 several days, and then to diminish. In the same way, a Cassiopeia has its period em- 

 braced in 225 days. And many other instances are known. It signifies nothing that 

 these periods are short. In the constitution of the universe, no value is attached to 

 time. With men, whose period of action is embraced in a few years, the different 

 events of life are circumscribed by measured spaces there is a limit beyond which hu- 

 man exertion cannot go ; and to adjust time and action to each other, and to measure 

 the one by the other, is our common duty. But in the administration of the universe 

 the case is different ; in eternity there are no limits of duration, and time can be ex- 

 pended without detriment or loss. In the pulsation of a wave of light, a part of the 

 millionth of a second is enough, and it is given. In the revolution of one system of 

 stars round another, millions of centuries are required, and they are consumed. And 

 so, in the case that we are considering, the glowing and fading away of one star may be 

 accomplished in a few days, but inconceivably great periods of time may be wanted for 

 the same events to transpire in another. Even philosophers are too prone to believe, 

 that by the short spaces of human life, or the history of nations, they can mark out pe- 



