66 ACCOUNT OF A BOY 



Here it may not be improper to mention, that his sister is 

 convinced, tliat he sees some objects better by moon-hght 

 than during tlie day ; a circumstance which seems to shew, 

 that tlie opacity in his eyes is, as in other cases of cataract, 

 merely local ; so that when the pupil is much dilated, some 

 rays of" light reach the retina, through those more transparent 

 parts of the humours \*hich are farther distant from the axis 

 of vision than the portion that is opaque. 



His powers of Hearing remain as imperfect as ever. He 

 still continues the practice of striking hard bodies against his 

 teeth ; but on further reflection, I think it not unlikely, that 

 he may have another object in view in this experiment, be- 

 sides that of procuring a sensation of sound. It is not at all 

 improbable, that he discovers differences in the hardness of 

 bodies in this manner. For there is a very distinct sensation 

 felt towards the roots of the teeth themselves, when they are 

 struck with a hard substance, resulting probably from an affec- 

 tion of the nerves of the membrane lining their inner cavity, 

 and this sensation is different according to the haidness of the 

 body. I have little doubt, that he could by this kind of feel- 

 ing alone, very easily discover that lead was softer than steel, 

 and steel harder than ivory ; although all these substances 

 would feel equally hard to his proper organs of touch. But 

 even supposing that he does not avail himself of this sensation 

 in the teeth themselves, it is probable that he strikes bodies 

 against these organs, not so much to try whether they will 

 cause sound at all, as to observe what kind of sounds they will 

 emit ; from which he may infer various other properties, 

 which experience has taught him, are invariably connected 

 with the particular sounds emitted. 



His manner of examining any object that is new to him, is 

 precisely the same now that it was four years ago, when I first 

 saw him. \Vlien it is put into his hand, he runs it over wath 



the 



