162 CHAPTER OF VARIETIES. 



choice of food, in which the evidence of sense at once determines be- 

 tween the injurious and the wholesome. Neither is instinct sagacity. 

 Brutal sagacity is in many instances very great ; but it is most easily 

 distinguishable from instinct, and in many respects stands perfectly con- 

 trasted with it. Sagacity, by exercise and tuition, may be improved 

 instinct cannot. Sagacity displays itself where the guidance of instinct 

 fails. Sagacity is most perfect and remarkable in creatures whose 

 instincts are few and simple ; as the dog, the horse, the elephant, and 

 the monkey. Sagacity is various in different individuals of the same 

 species ; instinct is uniform in every separate tribe. Sagacity in a 

 brute resembles reason in a man ; it is a contriving faculty : it observes 

 circumstances, and makes use of them ; it perceives difficulties, and 

 provides against them ; it can receive instruction, remember facts, and 

 profit by experience. But of instinct the exact reverse is true: it 

 works where contrivance and instruction, experience and observation, 

 are all alike impossible, and can be of no advantage. What, then, is 

 instinct ? A guiding faculty, given for a specific purpose ; within 

 which design it directs with unerring correctness, but beyond which it 

 has no light or power; equally effectual for any operation, however simple, 

 or however complex ; surpassing reason as much in the steadiness of its 

 operation and the certainty of its results, as it falls short in extent of 

 application and capability of improvement. A light to these humble 

 creatures emanating from the Father of lights, as much suited to their 

 necessities and happiness, as reason and revelation are to ours. But 

 of the particular nature of this guiding faculty, and of the mode in 

 which it operates, we can, perhaps, know no more than the individual 

 who possesses only the sense of hearing can comprehend of sight, 

 which he never enjoyed : he can be informed of its results and disco- 

 veries, as we can observe the wonders of instinct ; but in either case, 

 we must possess the faculty to enable us to do more than perceive its 

 effects, and give it a name." 



ON THE COLOURS OF NATURAL BODIES, BY SIR DAVID BREWSTER, 

 V. P. R. S. ED.* The only theory of the colours of natural bodies that 

 has met with reception in modern times, is that of Sir Isaac Newton, 

 who considers them as identical with those of thin plates, and as varying 

 with the size of the ultimate particles of the body. 



Although this theory, ingenious as it is, be liable to many great 



* Read before the Royal Society of Edinburgh. 



