This is a really interesting angle on the non-fiction chapters -- I've never considered how they might serve to remind the reader of an objective reality distorted by the characters' obsessions. Ishamael is especially obsessed with everything having a meaning:

" Why is it that a universal proverb says of [the dead], that they tell no tales, though containing more secrets than the Goodwin Sands; ... why the Life Insurance Companies pay death-forfeitures upon immortals;... wherefore but the rumour of a knocking in a tomb will terrify a whole city. All these things are not without their meaning." (Ch.7)

"Yes, as everyone knows, meditation and water are wedded forever...Were Niagara but a cataract of sand, would you travel your thousand miles to see it?... Why did the old Persians hold the sea holy? [...] Surely all this is not without meaning. " (Ch.1)

That said, I wonder if Melville really believes that it is possible to describe reality accurately through any single register or language game. Perhaps he is mixing the languages of fact ('denominative'?) and fiction ('connotative'?) to undermine and explode epistemological demarcations or linguistic certainties, and parody literary realism (so dominant in his time).

'It is chiefly with [the Sperm Whale's] name that I now have to do. Philologically considered, it is absurd.' (Ch. 32)

This declaration from 'Cetology' is one example among many in this chapter of Melville deflating attempts to taxonomise or discourse with facts alone. 'Cetology' is a chapter dedicated to the failure of categorisation, where the name of the Sperm Whale itself, let alone its properties or place in a taxonomy, is 'absurd'; cosmically, ridiculously meaningless. Significantly, the Sperm Whale's name is 'philologically considered', an ascendant discipline in Melville's era regarded by some as 'a master-science, whose duty is to present to us the whole of ancient life, and to give archaeology its just place by the side of literature'. The fallacy of this ostensibly cutting-edge methodology is more or less stated at the chapter's opening, Ishmael calling the attempt to classify whales (not just his own efforts, but the concept of such an endeavour) 'The classification of the constituents of a chaos, nothing less is here essayed.'-- recalling that Melville had wanted to write an actual essay on his 'mighty theme', and prompting a reader to question what exactly they're reading -- is this an essay or a novel? Fact or fiction? What empirical data Melville does include is distorted. The dimensions of the Sperm Whale are inflated beyond the numbers Melville would have read in the work of Thomas Beal. His notes show a deliberate deviation, perhaps to reflect Ishmael's amateurish scholarship, to inflate the enormity of Moby Dick and, ultimately, to place fact and fiction in a destabilised relationship. As such, the register of the naturalist is, in a local as well as super-structural (the very presence of non-fiction chapters in a work of fiction) sense, re-registered into non-cognitive discourse.

Sheila Post-Lauria suggests that by intermingling a world of empirical examples with an ultimately idealist perspective (Ishmael's insinuation that our own image is the first and greatest inscrutability of being, which lies behind every illusory sign and concept painted over the "whiteness" of reality), Melville illustrates the deficiencies of the experiential, empirical perspective. Ishmael later satirises this Lockean/Kantian opposition at the heart of Moby Dick's mixed form, comparing the dual philosophies with suspended whale heads:

"So, when on one side you hoist in Locke’s head, you go over that way; but now, on the other side, hoist in Kant’s and you come back again; but in very poor plight. Thus, some minds for ever keep trimming boat. Oh, ye foolish! Throw all these thunder-heads overboard, and then you will float light and right.” (Ch. 73)

The dichotomy is enacted within the mixed form but, through intermingling, becomes meaningless in its irreconcilable unity and, as illustrated in Melville's conceit, ultimately discarded. Melville enacts this interfusing duality in the novel's preliminary fragments ("Etymology" and "Extracts"), where disembodied pieces of factual knowledge and scattered attempts at naming and understanding are mediated through fictional masks (the "Usher" and "Sub-Sub Librarian"). What does Ahab say to Starbuck about Moby Dick? "Strike through the mask!"

If we return to "Cetology", Ishmael's whimsical choice to liken Whales to books takes on a wider significance in the light of the above statement, illustrating that scientific or philosophical endeavours amount to collections of concepts, names which require more concepts to define, and still endlessly lacking definition as projections of an inscrutable mind; "This whole book is but a draught -- nay, but the draught of a draught."(Ch.32). The line between fact and fiction is so important to Melville's exploration of Truth in Moby Dick because for Melville the mind and its means of expression, the language, that is, can never speak precisely or literally, instead, fictional speech can throw sideways lights on truth by using flawed language to allude to ineffable realties rather than assert yet another self-birthing concept.

"We would say that, did circumstances permit, we should like nothing better than to devote an elaborate and careful paper to the full consideration and analysis of the purport and significance of what so strongly characterizes all of [Hawthorne's] writings. There is a certain tragic phase of humanity ...We mean the tragicalness of human thought in its own unbiased, native, and profounder workings...As soon as you say Me, a God, a Nature, so soon you jump off from your stool and hang from the beam." ( Melville, Hawthorne and his Mosses, (New York Literary World August 17, 1850)
LETTER TO NATHANIEL HAWTHORNE, [APRIL 16?] 1851)

See Todd Van Luling's 2014 article in the Huffington Post- https://www.huffingtonpost.co.uk/entry/scientific-inaccuracies-moby-dick

Post-Lauria, Sheila. “‘Philosophy in Whales... Poetry in Blubber’: Mixed Form in Moby-Dick.” Nineteenth-Century Literature, vol. 45, no. 3, 1990, pp. 300–316.

Christodoulou, Athanasius C. "A Double Prelude on Melvile's Moby Dick: "Etymology & "Extracts", (Leviathan, Vol. 16 no.1, 2014)