When he first wrote, he said his starting point was to be a variation on the old Bordeaux question: What is the physical cause of variety in the species of humankind?

No one had made a significant attempt at it since the last century, so I was attracted, of course. What subject could be more attractive to a natural philosopher than such an investigation? I was sure God would guide this enquiry into an aspect of His creation. To begin with, Langton and I shared a hypothesis: that the differences between men are rooted in the composition of the body itself, that they are physiological and not, as some would have it, due to the vagaries of climate and other external factors, and therefore can be deciphered by a careful study of anatomy. Langton offered access to an unparalleled collection of skulls, and it was on my advice that he first thought to measure internal cranial capacity, not just the angles and planes every other bump-reader concerns himself with. I suggested he could do it by using mercury, or shot, to gain an accurate reading of internal volume.

I thought his examinations would be organized on the fundamental principles of phrenology, namely that the brain is the organ of the mind, its different parts perform different functions, and one can deduce certain characteristics of a man by its size and form. In this way, we proposed to compile a survey of the natural mental endowments of each race of men, as fashioned by their Creator. Each to match its own geography.

But Langton always resisted even divine attempts at guidance, so I should have seen there was very little chance he’d follow mine.

At the end of the first year, he wrote to inform me that he sought to go further than the original scope; to expand upon Maupertuis by proving that, if man is the product of the mechanical forces of conception, our traits, including race, are passed to us through sperm, and the Negro’s blackness is therefore innate, as well as the Negro’s other characteristics: inferior intellect and morality and ambition.

I wrote asking him what had happened to the skulls. He was still taking measurements, he replied.

He had done nothing with them! There was no catalogue. He had wasted all that time blistering corpses.

Worse, his project now pulled towards the argument that the origins of man are profane, not profound, that man is fashioned by sperm and not by God. Heresy, in other words. I could not be part of it. There was very little left of the phrenological study I thought we’d embarked on (though I believe now that may simply have been a pretext, to draw me in). Good intentions should never attach themselves to bad means.

Knowing that the greater name will always attract the greater tarnish, I told him I’d no longer sign my name to his project. I offered to purchase his skulls, since he had no idea how to examine them properly. I thought the matter would rest there, we’d go our separate ways. But instead he whitewashed his manuscript, excised all references to his doubtful experiments, and sought to persuade me that we could try again.