232 LETTERS ON NATURAL MAGIC. 



spoke with the workmen, and had some difficulty 

 in hearing them. This difficulty of hearing rose 

 to such a height, that during three or four 

 minutes I could not hear them speak. I could 

 not, indeed, hear myself speak, though I spoke 

 as loudly as possible ; nor did even the great 

 noise caused by the violence of the current 

 against the sides of the bell reach my ears." 



The effect thus described by Dr. Colladon is 

 different from that anticipated by Dr. Wollaston. 

 He was not merely deaf to low tones, but to all 

 sounds whatever ; and I have found, by repeated 

 experiment, that my own ears become perfectly 

 insensible even to the shrill tones of the female 

 voice, and of the voice of a child, when the drum 

 of the ear is thrown into a state of tension by 

 yawning. 



With regard to sounds of high pitch at the 

 other extremity of the scale, Dr. Wollaston has 

 met with persons, whose hearing was in other 

 respects perfect, who never heard the chirping of 

 the Gryllus campestris, which commonly occurs 

 in hedges during a summer's evening, or that of 

 the house-cricket, or the squeak of the bat, or 

 the chirping of the common house-sparrow. The 

 note of the bat is a full octave higher than that 

 of the sparrow ; and Dr. Wollaston believes that 

 the note of some insects may reach one octave 

 more, as there are sounds decidedly higher than 

 that of a small pipe, one-fourth of an inch in 

 length, which he conceives cannot be far from 

 six octaves above the middle E of the piano- 

 forte. " The suddenness of the transition," says 

 Dr. Wollaston, " from perfect hearing to total 

 want of perception, occasions a degree of surprise, 



