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This page contains excerpts of the article by Tiberius Cavallo (1749-1809) in the Philosophical Transactions of the Royal Society of London, volume 78 (1788) p.238-54. Cavallo was an Italian 'natural philosopher', meaning scientist, who made his home in London after 1771. His chief interest here was in the use of equal temperament, evidently a novelty, and the article is mainly useful for whatever light it sheds on the unequal tuning in use in 18th century England. Later, Cavallo was consulted by Broadwood about the design of pianos, though it is not clear how useful his 'scientific' advice was in the end.
In the article, Cavallo discusses temperament in general, and naturally begins with the pure intervals of the scale and the deduction that a keyboard instrument cannot contain every pure interval.
The choice between different pitches for A follows from its dual purpose as major sixth above C or perfect fifth above D.
These remarks already rule out any truly circulating or near-equal temperament.
This is the first clue to what the 'common' tuning could have been. However, it is evident that Cavallo has missed out or misstated some of the minor keys; it is impossible that G minor should be omitted from among the 'best' minors. Also, given the 'disagreeable' nature of F# major, it may be that B minor is a misprint. However, the fact that there are fewer 'good' minor than major keys is understandable, since minor tonality requires a greater harmonic range.
If we count the keys Cavallo mentions, the total number of more or less 'agreeable' keys reaches 13. Perhaps one more minor key ought to be added; at any rate, Cavallo's enumeration is not completely reliable.
The designation of both Ab and E major as 'less agreeable' points to a compromise pitch for G#/Ab, within a framework of modified meantone. If C-E were pure, then both E-G# and Ab-C could be made practically Pythagorean; any slight widening of C-E could go to improve one or both of the other thirds. The fact that B major and Db major are 'disagreeable' strongly suggests that the fifths C#-G#-D# were wide, probably making B-D# and C#-E# wider than Pythagorean. Other fifths, for example Eb-Bb, could be slightly wide without making Eb major significantly less agreeable.
It is perhaps surprising to see A major called 'less agreeable'. At any rate it probably indicates that C# was sharpened relative to the regular meantone framework of the central keys.
Cavallo here endorses unequal tuning, if one does not want to use all possible keys. You might ask: if, in fact, instruments are always tuned differently, what is the use of Cavallo's list of better and worse keys? We suppose that the players and tuners had, despite their differences, some tastes and practices in common, which is likely since no famous player could always be sure of having an instrument tuned in his peculiar manner.
The 'style of music' mentioned here probably means the choice of keys and range of modulation.
This remark strongly suggests that the Italian school of the early 18th century (to which Handel belonged) expected a more nearly equal keyboard tuning than was commonly used in late 18th century England. Cavallo clearly would recommend equal temperament for the accompaniments of such composers.
The next part of the article describes Cavallo's setting of equal temperament with the (questionable) help of a monochord.
A likely interpretation is that the key on a 'normally' tuned harpsichord that most resembled the effect of equal temperament was E major. A major would be more 'agreeable', and B major less. But if one takes Cavallo as saying literally that E-G# was the same as in equal temperament, it is not clear how to proceed in interpreting his previous remarks on differences between keys. The correspondence between ET and E major could not be exact.
Cavallo summarises:
We may or may not agree with Cavallo's judgement, but it is clear that later 18th century England was a place where very noticeably unequal tuning with strong differences between keys was the norm. This can scarcely have been anything other than modified meantone where the central keys had pure or nearly pure thirds.
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