Reflection of Light. 39 



Once now and then, looking at this range of hills 

 from a distance of two or three miles on moonless 

 nights, when it has been sufficiently clear to distin- 

 guish them, I have noticed that the particular down 

 on which the earthwork is situate shows more dis- 

 tinctly than the others. By day no difference is ap- 

 parent ; but sometimes by night it seems slightly 

 lighter in hue, and stands out more plainly. This 

 may perhaps be due to some unobserved character- 

 istic of the herbage on its slope, or possibly to the 

 chalky subsoil coming there nearer to the surface. 

 The power of reflecting light possessed by the earth, 

 and varied by different soils or by vegetation, is worth 

 observation. 



