202 SCIENTIFIC ILLUSTRATIONS [Lig 



many or too bright rays would dazzle vision, while too few 

 would leave it obscure and indistinct, an ever-vigilant sentinel 

 the iris, on which the colour depends is posted across the 

 front of the eye, to regulate by the expansion or contraction of 

 the pupil the exact number of rays that ought to be admitted. 

 The full blaze of light from the sun we could not endure. 

 Our mental eye has also been evidently designed to receive not 

 full but regulated light. Who could bear the full glare of the 

 brightness of the spiritual world? We have but reflected 

 and limited light. With our present faculties and duties we 

 must suppose that the arrangement is the one most suitable to 

 us. Let us at all events recognise the existence of fact. We 

 will neither pretend that we have seen the absolute glories of 

 the sun, nor of " the Light of the world." Our perceptive 

 organs have not been constructed for either purpose. BE. 



True Light has no Substitute. ,1 



Clear and brilliant light often brings out exquisite colours, 

 as happens among the Alps and also in the north frigid ;zone, 

 where the humble little plants called lichens and mosses are 

 in many cases dyed of the most brilliant hues, purple and 

 gold predominating. Warmth, in like manner, will stimulate 

 vegetable growth in the most astonishing manner, but it is 

 growth not necessarily accompanied by the secretion of valu- 

 able substances, such as give quality and real importance to 

 the plant. In English hot-houses, for example, we have 

 plenty of spice- trees, those generous plants that yield cinnamon 

 and cassia, the nutmeg and the clove; but although healthy 

 and blossoming freely, they never mature their aromatic secre- 

 tions. Though they have artificial heat equal to that of their 

 native islands, which burn beneath the sun of the Indian 

 Ocean, we cannot supply them with similar and proportionate 

 solar light. Our cloudy skies shut us in from the full and 

 direct radiance of the sunshine, and wanting this, heat alone 

 will not avail. LL 



