rays by means of the heliostat. Xevertheless, a judicious selection 

 of coloring matters and a logical method of performing our experi- 

 ments will lead to good results. I will give as proof that the recent 

 most careful experiments concerning the action of various rays upon 

 the production of oxygen by leaves and upon the production of the 

 green coloring matter have only confirmed the discoveries made in 

 183G, without either prism or heliostat, by Professor Daubeny, from 

 which it appears that the most luminous rays have the most' i^ower. 

 next to them the hottest rays, and lastly those called chemical. 



Doctor Gardner in 1843, Mr. Draper immediately after, and Dr. 

 C. M. (juillemin in 1857, corroborated by means of the prism and the 

 heliostat the discovery of Doctor Daubeny, which negatived the 

 opinions prevalent since the time of Senebier and Tessier, and which 

 were the results of erroneous experiments. It was difficult to believe 

 that the most refrangible rays, violet, for instance, which act the 

 most on metallic bodies, as in photometrical operations, should be 

 precisely those which have least effect in decomposing the carbonic- 

 acid gas in plants and have the least effect over the green matter in 

 leaves. Notwithstanding the confirmation of all the experiments 

 made by Doctor Daubeny, when repeated by numerous physicists and 

 by more accurate methods, the old opinions, appearing more probable, 

 still influenced many minds till Prof. Julius Sachs, in a series of very 

 important experiments, again affirmed the truth. It is really the 

 yellow and orange rays that have the most power, and the blue and 

 violet rays the least, in the phenomena of vegetable chemistry, con- 

 trary to that which occurs in mineral chemistry, at least in the case 

 of chlorid of silver. The least refrangible rays, such as orange and 

 yellow, have also the twofold and contrary property, such as pertains 

 also to white light, and which produces the green coloring matter of 

 leaves or bleaches them according to its intensity. It is these, also, 

 which change the coloring matter of flowers when it has been dis- 

 solved in water or alcohol. Those rays called chemical, such as violet 

 and the invisible rays beyond violet, according to recent experiments 

 confirmatory of those of ancient authors — those of Sebastian Pog- 

 gioli in 1817 and those of C. M. Guillemin — have but one single 

 well-ascertained effect, that of favoring the bending of the stem 

 toward the quarter from which they come more decidedly than do 

 other rays; yet that is an effect perhaps more negative than positive 

 if the flexure proceeds, as many still believe, from what is going on on 

 the side least exposed to the light. 



The effect upon vegetation of the nonvisible calorific rays at the 

 other extremity of the spectrum has been but little studied. Accord- 

 ing to the experiments we have on this subject, they would appear to 

 have but little power over any of the functions; but it would be 

 Avorth while to investigate further the 'calorific regions of the spec- 

 trum by employing Doctor Tyndall's process — that is, by means of 

 iodine dissolved in bisulphide of carbon — which permits no trace of 

 visible light to pass. 



How interesting it would be to make all these laboratory experi- 

 ments on a large scale ! Instead of looking into small cases or into 

 a small apparatus held in the hand and in which the plants can not 

 well be seen, the observer would himself be inside the apparatus and 

 could arrange the plants as desired. He might observe several 

 species at the same time — plants of all habits, climbing plants, sensi- 



