V. 



THE PHASTS OF FORCE.* 



[In the earlier part of the article, Dr. Carpenter referred to "a few of the 

 "more striking and typical examples o{ \\\q phasis of matter, for the purpose of 

 "introducing a kindred topic, the phasis of force.''' After ilkistnting the 

 mutual correlation of mechanical force, heat, chemical affinity, and electricity, 

 he dealt with light, passing from its relation to the preceding modes of force, 

 to describe its effects in influencing vital processes, and thus advancing to the 

 phenomena of life.] 



In by far the larger number of cases in which Light is evolved, 

 its manifestation can be directly traced to chemical combination ; 

 whilst, conversely, light is often a most powerful agent in bringing 

 about chemical change. In fact, it may be doubted whether light 

 does not alter the structure or composition of all matter through 

 which it passes, or on which it falls. Upon such an alteration 

 depend, not only all the phenomena of photography, and numerous 

 chemical changes of a most important character, but also the 

 sustentation of all organic life, and our own sensibility to visual 

 phenomena. For it is by the extraordinary influence of light upon 

 the surface of the growing plant, that it is able to separate the 

 inorganic elements of water, carbonic acid, and ammonia, and to 

 unite them into those new and peculiar compounds — starch, oil, 

 albumen, and their derivatives — which serve, not only for the 

 extension of the vegetable fabric, but also for the nutrition of the 

 animal body ; so that without light, as Lavoisier truly said, nature 

 were without life and without soul. So, again, there can be no 

 doubt that it is by directly producing some change in the nervous 

 tissue of the retina, of which change the result is transmitted to 



* National Review, April, 1S57. 



