I am completing the *final* section of my *final* incomplete chapter (fingers-crossed) and one of the questions it has raised is what influence the work of Euler had on Cullen’s thinking (or perhaps I should say the Eulers, but I am here primarily thinking of the work of the elder Euler, Leonhard [1707-83]). These two are not usually linked together. Indeed, Cullen has been called – somewhat mistakenly in my view – a typically ‘Scottish’ thinker, but again and again I keep seeing the influence of Continental physicians (Boerhaave, Haller, Gaubius, Stahl) and natural philosophers on his own system of the natural world.

A particularly fruitful and interesting topic in this regard is Cullen’s understanding and use of a subtle matter, or aether, in the many areas of medicine and philosophy that interested him. It has been pointed out by Christie and others that in some of Cullen’s chemical writings, his view of the Aether and its role in physiology shares similarities with the work of the Irish physician, Bryan Robinson, especially in his *A **Dissertation on the Aether of Sir Isaac Newton* (1743). And Cullen makes explicit reference to Robinson’s work, a number of times (e.g. in his c.1761 chemical lectures). But, as we go later into the 1760s and look at Cullen’s lectures on the institutions of medicine, a new name crops up where Robinson’s name used to be: Euler. Although Cullen had a copy of Euler’s 1746 *Opuscula Varii Argumenti *(which contained Euler’s influential new theory on light and colour) in his library upon his death, it remains unclear when the significance of Euler’s work dawned on him. I conjecture sometime between 1761-1766, though whether this was on account of Cullen’s first reading of Euler’s theory or through another channel may not be possible to say (though a thorough review of Cullen correspondence might be where to look).

Through the generosity of an older scholar who has done important work on Euler, Newton and Aepinus, I have been able to obtain an unpublished English translation of Euler’s 1746 essay, and I have to say that I have been extremely impressed with its clarity and rhetorical persuasiveness. It is heads above the work of Robinson and Hartley, for instance, and reads – even in translation – as a suitable successor to Newton’s own work on light and colours (with which it takes issue).

In any case, since Cullen – in his defense of his belief in the existence of a nervous elastic fluid that was a modification of the universal Newtonian Aether – claims to agree with Euler’s system of nature (at least as of early 1769), I have thought it worthwhile to spend a little time reading Euler’s theory and some of the secondary literature on it. Euler may be better known for his mathematics, but he was no slouch in optics and other areas of natural philosophy either.

Cullen, I think, would happily agree.