C H9 ) 
A Letter of Dr, John Wallis to Sa- 
Mr. Harris an Organ-maker ( whom I find, by the little 
difcourfe I had with him, to be very well skilled in his 
profeffion ) was lately with me, as by dire6lion from you, to 
ask my opinion about perfefting an Organ, in a point wherein 
he thinks it yet Imperfedt. 
'Tis an honour you pleafe to put upon me, to think my 
opinion confiderable in a thing wherein I am fb little acquaint- 
ed as that of an Organ. 
I do not pretend to be perfedlly acquainted with the Stru^^ 
(Sure of an Organ, its leveral Parts, and the Incidens there- 
unto ; Having never had Occafion and Opportunity to inform 
my felf particularly therein. And, for the fame reafon, many 
of the Words, Phrafo, Forms of Speech, and Terms of Arc, 
which are familiar to Organifts and Organ makers, are notfo 
to me. Which therefore I fliall wave ; ( For till we perfectly 
iinderftand one anothers Language, it is not eafy to fpeak intel- 
ligibly ; ) and apply my felf directly to what is particularly 
This { I take it ) is evident ; That each Tipe in the Organ is 
intended to exprefs a diftinft Sound zt fuch a Titch\ That is, in 
fiich a determinate Degree of Gravity or Acutenefs ; or ( as it is 
now called ) Flatnefs or Sharpnefs, And the Relative or Com- 
parative QoviMtxzxion of Two ( or more ) fuch Sounds or De- 
grees of Flatnefs and Sharpnefs, is the ground of ( what we 
call ) Concord and Z>iJcord; that is, a Soft, or Harfli, coincidence. 
Now, concerning this, there were amongft the Ancient 
Greeks, Two (the mofl confiderable ) Se^s of Muficians : the 
AriJloxenianSy and ^tTythagorians. 
They both agreed thus far ; That Dia-teffmn and "Dia-pente^ 
do 
