344 Light and Darkness. [July, 



however, is not certain, and as we are still ignorant of the exact 

 relation which tissue disintegration bears to work, we cannot as yet 

 pretend to determine a priori the quantity of flesh-formers neces- 

 sary under conditions of work. The practical solution which expe- 

 rience has provided for the problem must for the present rule our 

 dietary scales, although it can hardly be doubted that a more scien- 

 tific knowledge upon the subject will before long be gained. 



IV. LIGHT AND DAEKNESS. 



Winslow on Light.* — Johns on the Blind.! 



Regarding the nature of Light, there have been, and perhaps may 

 still be said to be, two distinct theories extant. The older view 

 conceives of light as a form of matter, infinitely diffused, but still 

 matter, which is itself projected from the light-emitting body, and 

 falls upon the surrounding objects ; the newer theory treats light as 

 a force, and necessitates the belief in an interplanetary Ether, also a 

 form of matter infinitely attenuated, but capable of being agitated 

 in waves by the luminous force. The latter or undulatory theory 

 of light, which makes it to be a mode of motion, is now almost com- 

 pletely established, and although the human mind cannot yet form 

 a proper conception of the interplanetary ether, the medium acted 

 upon, still that may be said also to be one of the acknowledged 

 facts of physical science. 



Around this subject cluster many eminent reputations ; that of 

 Newton stands out the most prominent; it was he who first 

 analyzed a ray, and showed it to be far more complicated than it 

 appeared to be without the intervention of .the prism. The elder 

 Herschel and Eitter revealed the character of the non-luminous but 

 calorific, and chemical, or as Eobert Hunt has called them, the 

 Actinic Eays. Stokes, Hunt, Locke, Joule, Balfour Stewart, 

 Tyndall, and many others, have added to our knowledge of the 

 nature and effect of light; and yet that knowledge is but in its 

 infancy. 



Wonderful as are the operations of fight upon inanimate nature, 

 operations which have caused it to be employed in photography to 

 perpetuate the memory of the living and to recall most vividly the 

 history of the past ; still more wonderful is its influence upon living 

 forms, whether in the animal or plant world. 



* ' Light— its Influence on Life and Health/ By Forbes Winslow, M.D., D.C.L., 

 Oxon. Longmans. 



f ' Blind People : their Works and Ways, with Sketches of the Lives of Some 

 Famous Blind Men.' By Bev. B. Gr. Johns, M.A., Chaplain of the Blind School, 

 St. George's Fields. Illustrated. John Murray. 



