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APPENDIX. VI. 
If a dozen singing birds of different kinds 
are heard in the same room, there is not any, 
disagreeable dissonance (which is not properly 
resolved), either to my own ear, or to that of 
others, on whose judgment on such a point I 
can more rely. 
At the same time, as each bird is singing a 
different song, it is extraordinary that what we 
call harmony should not be perpetually violat- 
ed, as we experience, in what is commonly 
called a Dutch concert, when several tunes are 
played together. 
The first requisite to make such sounds 
agreeable to the ear is, that all the birds should 
sing in the same key, which I am induced to be- 
lieve that they do, from the following reasons. 
I have long attended to the singing of birds, 
but if I cannot have recourse to an instrument 
very soon, I cannot carry the pitch of their 
notes in my memory, even for a very short 
time. 
I therefore desired a very experienced harpsi- 
chord-tuner (who told me he could recollect any 
particular note which he happened to hear for 
several hours), to mark down when he returned 
home what he had observed on this head. 
I had lately received an account from him 
of the following notes in different birds. 
