Quote:One evening Ferguson went to a weekly gathering (probably a dining or drinking club), where one of the other people present, a watchmaker, 'began to hold forth against a Trinity of persons in the God-head, wondering at the impudence of the person who broached such an absurd doctrine'. Ferguson, who was sitting just opposite to him, 'gave him a severe frowning look', whereupon the watchmaker asked his opinion concerning the Trinity. Ferguson suggested that they should talk about the watchmaker's business instead, and asked him whether he understood how one gear wheel turned another. 'I hope I do, said he'.
‘Then, said I, suppose you make one wheel as thick as other three, and cut teeth in them all, and then put the three thin wheels all loose on one axis, and set the thick wheel to them, so that its teeth may take into those of the three thin ones; now turn the thick wheel round: how must it turn the others? Says he, your question is almost an affront to common sense; for everyone who knows anything of the matter must know that, turn the thick wheel which way you will, all the other three must be turned the contrary way by it. Sir, said I, I believe you think so. Think! says he, it is beyond a thought - it is a demonstration that they must. Sir, said I, I would not have you be too sure, lest you possibly be mistaken; and now what would you say if I should say that, turn the thick wheel whichever way you will, it shall turn one of the thin wheels the same way, the other the contrary way, and the third no way at all. Says he, I would say there was never anything proposed that could be more absurd, as being not only above reason, but contrary thereto. Very well, says I. Now, Sir, is there anything in your ideas more absurd about the received doctrine of the Trinity than in this proposition of mine? There is not, said he; and if I could believe the one, I should believe the other too.’
Ferguson then said that he could make such a machine, and would bring it along to show to the assembled company the following week. He did so, and asked the watchmaker to explain it. The watchmaker turned it to and fro, took it to pieces and put it back together again, and confessed that he was thoroughly perplexed. 'The thing is not only above all reason, but it is even contrary to all mechanical principles'.
‘For shame, Sir, said I, ask me not how it is, for it is a simpler machine than any clock or watch that you ever made or mended; and if you may be so easily non-plused by so simple a thing in your own way of business, no wonder you should be so about the Trinity; but learn from this not for the future to reckon every thing absurd and impossible that you cannot comprehend.’