ECHOES OF BATS AND MEN 



even here where the word was a short one the echoes be- 

 gan to mix with the original sound waves long before 

 the end of the word. 



Despite all these differences in the photographic por- 

 trait, the same word spoken in these two situations 

 sounds about the same. Again the amazing fact is that 

 all these special procedures are necessary to convince us 

 that the two sets of sound waves are not exactly the 

 same. We have no difficulty recognizing the word or in 

 telling who said it; it really does not sound very different 

 in the living room from on the sidewalk. Why not? An- 

 other simple experiment with a tape recorder throws 

 considerable light on this question. If we place the tape 

 recorder in an ordinary room (or, better still, a fairly 

 large hallway or schoolroom with hard walls) and make 

 a recording of a short sharp sound, we can play it back 

 and hear it rather faithfully reproduced. Let us suppose 

 that such a recording includes several repetitions of 

 short words ending in hard consonants, such as bit, took, 

 sud, or leg. Sharp clicks such as one can make by snap- 

 ping together a pair of large scissors or pUers may also 

 be used; and if one wishes a good excuse for it, a cap- 

 pistol report is excellent for this experiment. In any 

 event each recorded sound should be separated from 

 the next by a few seconds of quiet. 



When such a tape recording has been made, play it 

 backward. That is, interchange the two reels so that the 

 tape moves back end first when the machine is playing 

 back the recording. What used to be the take-up reel 

 becomes the reel from which the tape is unwound and 

 vice versa. It will only be necessary on many recorders 

 to turn the two reels upside down when interchanging 

 them, so that the same side of the tape will pass next to 

 the recording head. On some machines only half the 

 width of the tape is magnetized when a recording is 



62 



