I want to mention a very long title which doesn’t have a good shortening using one continuous chunk:
An account of a method of dividing astronomical and other instruments, by ocular inspection; in which the usual tools for graduating are not employed; the whole operation being so contrived, that no error can occur but what is chargeable to vision, when assisted by the best optical means of viewing and measuring minute quantities
My instinct is something like:
A method of dividing astronomical … instruments, by ocular inspection
Which is kind of wordy itself and eliding middle of a title also seems strange.
I couldn’t really find any recommendations for formating wordy titles like this one when I went googling for writing style-specific rules or general suggestions.
How should this title be shortened? In general, how should very long titles like this be shortened? And, optionally, what should I have googled to find the answer to this question?
The Chicago Manual of Style, sixteenth edition (2010) has this to say about "very long titles":
14.106 Older titles and very long titles. Titles of works published in the eighteenth century or earlier may retain their original punctuation, spelling, and capitalization (except for whole words in capital letters, which should be given an initial capital only). Very long titles may be shortened in a bibliography or a note, omissions being indicated by three ellipsis dots within a title and four at the end [cross reference omitted].
[Example:] Escalante, Bernardino. A Discourse of the Navigation which the Portugales doe make to the Realmes and Provinces of the East Partes of the Worlde…. Tanslated by John Frampton. London, 1759.
Although this guideline applies specifically to bibliographies and notes, it doesn’t require that the full title appear elsewhere in the article or book containing the citation, so I imagine that one might take 14.106 as authority for truncating very long titles in main text as well as in notes and back matter. That being the case, I would recommend shortening the title that you ask about to this:
An account of a method of dividing astronomical and other instruments, by ocular inspection….
And because the actual original title of Edward Troughton’s book was set in all caps, I would follow Chicago’s advice to render it in initial caps (or more precisely, title case):
An Account of a Method of Dividing Astronomical and Other Instruments, by Ocular Inspection….
In fact, the title page of the book shows a fairly clear hierarchy within the title—the primary block consisting of
An Account of a Method of Dividing Astronomical and Other Instruments, by Ocular Inspection;
the secondary block consisting of
In Which the Usual Tools for Graduating Are Not Employed;
and the tertiary block consisting of
The Whole Operation Being So Contrived, That No Error Can Occur but What Is Chargeable to Vision, When Assisted by the Best Optical Means of Viewing and Measuring Minute Quantities.
The Oxford Guide to Style (2002) offers similar advice in its subsection headed "Long titles":
In general, long and superfluous subtitles may be discreetly omitted, especially in notes. Titles of older works may retain the original style, and may be shortened if very long winded:
[Example:] Henry Burton, A Divine Tragedie lately acted or … Gods Judgements upon Sabbath-breakers, and other libertines … (London, 1636).
Note that Oxford doesn’t endorse Chicago’s four-ellipsis-point style for end-of-title omissions.