52 ANNIVEESAET ADDRESS 



perpetual motion, it pi'obably moves in a circle. I cannot imagine 

 matter and force moving in straight lines, from the eternity past to 

 the eternity to come, through infinite space. The plan of nature 

 probably is perpetual circular motion. Of course it is impossible 

 for man to construct any machine that can have perpetual motion, 

 for this reason — part of the force with which the machine is 

 endowed must escape and be absorbed and used by surrounding 

 bodies. But taking the universe, where no part of matter or force 

 can really be lost, perpetual circular motion is not only possible, 

 but it is the only theory which will account for nature always con- 

 tinuing the same. 



The prevalence of this law is seen whether we examine the 

 macrocosm or the microcosm. First, we will select some examples 

 from the greater world or universe, and Astronomy affords some 

 marked examples. Our moon revolves round our earth, the earth 

 round the sun. The sun is moving at a rate of not less than 

 400,000 miles a day. He is thought to be moving round a star 

 called Alcyone, in the constellation Pleiades. This journey of the 

 sun would take 22| millions of years ; or, if he is moving round 

 the group of stars called the Pleiades, his year would be 27^ 

 millions of years. The proportion to our year of this solar year 

 which I will consider — say 25 millions of years — is not far from a 

 year to a second. The velocity of the sun in his gigantic orbit is 

 about 780 millions of miles in a year. Light travels from the sun 

 to our earth in little more than eight minutes. It would take 

 nearly 1000 years to reach us from our sun's sun. It is possible 

 that our sun's sun, Alcyone, with all his attendant planet-suns and 

 their planets and satellites, may be himself revolving around some 

 other centre. 



As our sun, although he is himself a planet, is the centre of our 

 system, it is important to have correct notions of him. I must 

 detain you for a moment while I endeavour to answer the question 

 "Why does the sun shine?" Sir John Herschel says, after 

 enumerating various theories which have been advanced, that 

 there remain only three possible sources of the heat of the sun — 

 electricity, friction, and vital action. I will not detain you by 

 enumerating the various theories ; they most of them have this great 

 defect — they attribute it to a temporary cause. But to my mind 

 a cause must be found that will account for the sun and also nature 

 having been the same for a time so long that it is impossible to 

 conceive it, and that it will continue the same. But supposing we 

 could account for the sun's force by combustion, or the friction of 

 meteoric matter, or original heat, yet a still greater difficulty 



