Great Principle of all we see,
Thou endless Continuity!
By thee are all our angles gently rounded,
Our misfits are by thee adjusted,
And as I still in thee have trusted,
So let my methods never be confounded!
O never may direct Creation
Breach in upon my contemplation,
Still may the causal chain ascending,
Appear unbroken and unending,
And where the chain is best to sight
Let viewless fancies guide my darkling flight
Through aeon-haunted worlds, in order infinite.
The third stanza of Scottish physicist James Maxwell's last dying poem, which references Scottish physicist Peter Tait and Balfour Stewart's 1875 principle of continuity, which he was wrestling with at the time, summarizing his views on life and death in the context of the modern physical science. [3]
In science, the principle of continuity, or doctrine of continuity, posits that that there is some form of continuity of existence or "continuity of the inter-conversion of the forces" that give rise to the motion throughout the universe, in relation to termination of the movement or existence of a person, according to the laws of modern physical science.

History
The term "continuity", supposedly, derives from Welsh physicist William Grove's 1846 book The Correlation of the Physical Forces. [4] In the original sense of the term “continuity” may be possibly found in the following 1842 lecture extract of Grove, and the premise that force is conserved or that there is a continuity among the operations of the following physical phenomenon that exists throughout the universe:

Physical science treats of matter, and what I shall to-night term its affections; namely, attraction, motion, heat, light, electricity, magnetism, chemical-affinity. When these re-act upon matter, they constitute forces. The present tendency of theory seems to lead to the opinion that all these affections are resolvable into one, namely, motion: however, should the theories on these subjects be ultimately so effectually generalized as to become laws, they cannot avoid the necessity for retaining different names for these different affections; or, as they would then be called, different modes of motion. Each force is definitely and equivalently convertible into any other and that where experiment does not give the full equivalent, it is because the initial force has been dissipated, not lost, by conversion into other unrecognized forces. The equivalent is the limit never practically reached.”

In other words, "continuity" seems to imply or be synonymous or shorthand for "inter-conversion of forces".

Whatever the case, Grove's The Correlation of the Physical Forces was referenced as the basis of Scottish physicists Peter Tait and Balfour Stewart's usage of the term in respect to their so-called "principle of continuity", with which the attempted to explain death in the guise of a mixture of modern physical science and religion. The Tait-Stewart version of the "continuity", as contrasted with the original Grove version, to note, seems to have been bowdlerized to some extent, expunging parts not amenable to certain Christian dogma.

In short, Tait and Stewart, attempted to outline a type of physics-based afterlife theory, which they presented "anonymously" in their 1875 book The Unseen Universe: or Speculations of a Future State. The book was a sort of precipitate theory or reactionary derivative of the 1874 BAAS Tyndall-Stewart-Tait debate on the overlap of modern physical science and religion. [1]

A laymanized version of the principle of continuity was presented in fictional form in the followup 1878 novel Paradoxical Philosophy: a Sequel to the Unseen Universe, followed by discussion of the implications of these ideas by Scottish physisict James Maxwell in his 1878 review article “Paradoxical Philosophy”, wherein he alludes to the idea of the paradoxical philosopher, all of which was summed up in his last and final dying poem “A Paradoxical Ode” (see above excerpt). [2]

References
1. Stewart, Balfour and Tait, Peter G. (1875). The Unseen Universe: or Physical Speculations on a Future State (continuity, 29+ pgs; section 61: principle of continuity, pgs. 53-61). Macmillan
2. (a) Stewart, Belfour and Tait, Peter G. (1878). Paradoxical Philosophy: a Sequel to the Unseen Universe. Macmillan.
(b) Maxwell, James. (1878). “Review: Paradoxical Philosophy”, in: Scientific Papers, II, pg. 451; in Nature, 19 (19 Dec 1878): 141-43; in: Scientific Papers, 2, 756-62.
3. (a) Maxwell, James. (1878). “A Paradoxical Ode / After Shelley”, in: Life of Maxwell, pgs. 649-51; in: Knott, Life of Tait, pgs. 242-43.
(b) Knott, Cargill G. (1911). Life and Scientific Work of Peter Guthrie Tait (Maxwell's review + "A Paradoxical Ode", pg. 241-43). Cambridge University Press.
4. Grove, William R. (1846). The Correlation of Physical Forces (6th ed.). London: Longmans, Green, 1874.

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