Simpson's methos of determining tuning

[Bill Hibbert]

At the end of Simpson's second paper, he explains that he has a 
method of accurately discriminating and determining partial tones, 
which he had been using for about 23 years and about which he says:

'If any of my readers are really desirous of making themselves 
masters of this "art," a letter addressed to the writer at 
Fittleworth Rectory, Sussex, shall receive every attention; and I 
can promise to founders a most valuable help in their difficult 
work, and to any lover of music a fruitful source of interest and 
pleasure.'

Does anyone have any idea how Simpson did this? A correspondent has 
just asked, and I had to confess I had no idea.

Bill H