Taylor - Theoretic Arithmetic.pdf - Platonic Philosophy
Taylor - Theoretic Arithmetic.pdf - Platonic Philosophy
Taylor - Theoretic Arithmetic.pdf - Platonic Philosophy
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BOOK Two 117<br />
by length, breadth, and depth, two middle terms of this kind<br />
are found, which having three intervals, are either produced<br />
from equals, through equals equally, or from unequals to unequals<br />
equally, or from unequals to equals equally, or after<br />
some other manner. And thus, though they preserve an harmonic<br />
ratio, yet being compared in another way, from the<br />
arithmetical middle; and to these, the geometric proportionality<br />
which is between both, cannot be wanting.<br />
Let the following, therefore, be an instance of this arrangement,<br />
viz. 6. 8. 9. 12. That all these then are solid quantities,<br />
cannot be doubted. For 6 is produced from 1 X 2 X 3; but 12<br />
from 2 X 2 X 3. Of the middle terms, however, between these,<br />
8 is produced from 1 X2X4; but 9 from 1 X3X3. Hence<br />
all the terms are allied to each other, and are distinguished by<br />
the three dimensions of intervals. In these, therefore, the geometric<br />
proportionality is found, if 12 is compared to 8, and 9<br />
to 6; for 12 : 8 : : 9 : 6. And the ratio in each is sesquialter.<br />
But the arithmetical proportionality will be obtained, if 12 is<br />
compared to 9, and 9 to 6; for in each of these the difference<br />
is 3, and the sum of the extremes is the double of the mean.<br />
Hence we find in these, geometrical and arithmetical proportion.<br />
But the harmonic proportionality may also be found in<br />
these, if 12 is compared to 8, and again 8 to 6. For as 12 is to 6,<br />
so is the difference between 12 and 8, i.e. 4, to the difference between<br />
8 and 6, i.e. 2. We may likewise here find all the musical<br />
symphonies. For 8, when compared to 6, and 9 to 12,<br />
produce a sesquitertian ratio, and at the same time the symphony<br />
diatessaron. But 6 compared to 9, and 8 to 12, produce a<br />
sesquialter ratio, and the symphony diapente. If 12 also is<br />
compared to 6, the ratio will be found to be duple, but the<br />
symphony diapason. But 8 compared to 9, forms the epogdous,<br />
which in musical modulation is called a tone. And this is the<br />
common measure of all musical sounds; for it is of all sounds