[The third of these discourses is the address “On the Physical Basis of Life,” of which he writes to Haeckel on January 20, 1869:—­]

You will be amused to hear that I went to the holy city, Edinburgh itself, the other day, for the purpose of giving the first of a series of Sunday lectures.  I came back without being stoned; but Murchison (who is a Scotchman you know), told me he thought it was the boldest act of my life.  The lecture will be published in February, and I shall send it to you, as it contains a criticism of materialism which I should like you to consider.

[In it he explains in popular form a striking generalisation of scientific research, namely, that whether in animals or plants, the structural unit of the living body is made up of similar material, and that vital action and even thought are ultimately based upon molecular changes in this life-stuff.  Materialism! gross and brutal materialism! was the mildest comment he expected in some quarters; and he took the opportunity to explain how he held] “this union of materialistic terminology with the repudiation of materialistic philosophy,” [considering the latter] “to involve grave philosophic error.”

[His expectations were fully justified; in fact, he writes that some persons seemed to imagine that he had invented protoplasm for the purposes of the lecture.

Here, too, in the course of a reply to Archbishop Thompson’s confusion of the spirit of modern thought with the system of M. Comte, he launched his well-known definition of Comtism as Catholicism minus Christianity, which involved him in a short controversy with Mr. Congreve (see “The Scientific Aspects of Positivism,” “Lay Sermons” page 162), and with another leading Positivist, who sent him a letter through Mr. Darwin.  Huxley replied:—­]

Jermyn Street, March 11, 1869.

My dear Darwin,

I know quite enough of Mr. —­ to have paid every attention to what he has to say, even if you had not been his ambassador.

I glanced over his letter when I returned home last night very tired with my two nights’ chairmanship at the Ethnological and the Geological Societies.

Most of it is fair enough, though I must say not helping me to any novel considerations.

Two paragraphs, however, contained opinions which Mr. —­ is at perfect liberty to entertain, but not, I think, to express to me.

The one is, that I shaped what I had to say at Edinburgh with a view of stirring up the prejudices of the Scotch Presbyterians (imagine how many Presbyterians I had in my audiences!) against Comte.

The other is the concluding paragraph, in which Mr. —­ recommends me to “Read comte,” clearly implying that I have criticised Comte without reading him.

You will know how far I am likely to have committed either of the immoralities thus laid to my charge.

At any rate, I do not think I care to enter into more direct relations with anyone who so heedlessly and unjustifiably assumes me to be guilty of them.  Therefore I shall content myself with acknowledging the receipt of Mr. —­’s letter through you.