ANIMALS. 31 



lently, or too perseveringly employed us, is paint- 

 ed upon every thing we look at, and mixes with 

 every object that occurs. " And this is an obvi- 

 ous consequence of the eye taking in too much 

 light, either immediately, or by reflection. Every 

 body exposed to the light for a time, drinks in a 

 quantity of its rays, which, being brought into 

 darkness, it cannot instantly discharge. Thus 

 the hand, if it be exposed to broad day-light for 

 some time, and then immediately snatched into a 

 dark room, will appear still luminous ; and it will 

 be some time before it is totally darkened. It is 

 thus with the eye ; which, either by an instant 

 gaze at the sun, or a steady continuance upon 

 some less brilliant object, has taken in too much 

 light ; its humours are for a while unfit for vision 

 until that be discharged, and room made for rays 

 of a milder nature." How dangerous the look- 

 ing upon bright and luminous objects is to the 

 sight, may be easily seen from such as live in 

 countries covered for most part of the year with 

 snow, who become generally blind before their 

 time. Travellers who cross these countries are 

 obliged to wear a crape before their eyes, to save 

 their eyes, which would otherwise be rendered 

 totally unserviceable ; and it is equally dangerous 

 in the sandy plains of Africa. The reflection of 

 the light is there so strong, that it is impossible to 

 sustain the effect without incurring the danger of 

 losing one's sight entirely. Such persons, there- 

 fore, as read or write for any continuance, should 

 choose a moderate light, in order to save their 

 eyes ; and although it may seem insufficient at 



