136 ANNUAL OF SCIENTIFIC DISCOVERY. 



only when they are under the influence of the sun. A portion of the sun's 

 rays exhibits a remarkable relation to chemical forces, it can produce and 

 destroy chemical combinations ; and these rays, which for the most part are 

 blue or violet, are called therefore chemical rays. We make use of their 

 action in the production of photographs. Here compounds of silver are de- 

 composed at the place where the sun's rays strike them. The same rays 

 overpower in the green leaves of plants the strong chemical affinity of the 

 carbon of the carbonic acid for oxygen, give back the latter free to the at- 

 mosphere, and accumulate the other, in combination with other bodies, as 

 woody fibre, starch, oil, or resin. These chemically active rays of the sun 

 disappear completely as soon as they encounter the green portions of the 

 plants, and hence it is that in daguerreotype images the green leaves of 

 plants appear uniformly black. Inasmuch as the light coming from them 

 does not contain the chemical rays, it is unable to act upon the silver com- 

 pounds. 



Hence a certain portion of force disappears from the sunlight, while com- 

 bustible substances are generated and accumulated in plants ; and we can 

 assume it as very probable, that the former is the cause of the latter. I 

 must indeed remark, that we are in possession of no experiments from which 

 we might determine whether the vis viva of the sun's rays which have dis- 

 appeared, corresponds to the chemical forces accumulated during the same 

 time ; and as long as these experiments arc wanting, we cannot regard 

 the stated relation as a certainty. If this view should prove correct, we 

 derive from it the flattering result, that all force, by means of which our 

 bodies live and move, finds its source in the purest sunlight ; and hence we 

 arc all, in point of nobility, not behind the race of the great monarch of 

 China, who heretofore alone called himself Son of the Sun. But it must 

 also be conceded, that our lower fellow-beings, the frog and leech, share the 

 same ethereal origin, as also the whole vegetable world, and even the fuel 

 which comes to us from the ages past, as well as the youngest offspring 

 of the forest with which we heat our stoves and set our machines in mo- 

 tion. 



You see, then, that the immense wealth of ever-changing meteorological, 

 climatic, geological, and organic processes of our earth are almost wholly 

 preserved in action by the light and heat-giving rays of the sun ; and you 

 see in this a remarkable axample, how Proteus-like the effects of a single 

 cause, under altered external conditions, may exhibit itself in nature. Be- 

 sides these, the earth experiences an action of another kind from its central 

 luminary, as well as from its satellite the moon, which exhibits itself in the 

 remarkable phenomenon of the ebb and flow of the tide. 



Each t>f these bodies excites, by its attraction upon the waters of the sea, 

 two gigantic waves, which flow in the same direction round the world, as 

 the attracting bodies themselves apparently do. The two waves of the 

 moon, on account of her greater nearness, are about three and a half times 

 as large as those excited by the sun. One of these waves has its crest on 

 the quarter of the earth's surface which is turned towards the moon, the 

 other is at the opposite side. Both these quarters possess the flow of the 



