That blog put forth a few possible reasons, none of which panned out. I find no sign that thirty came from “XXX” for end of story, or that AP writers had a quota of 30 stories, or that 30 was a typesetting symbol. I also find no evidence of a news editor named “Thirtee”. A favored theory seems to link the use of 30 to Civil War press telegraphs.
Then I found this, which I thought would settle the issue. It was a reference to the use of “30 dashes” in this 1936 book “Newspaper Makeup” by John Edward Allen:
“Many newspaper makeup men make the mistake of putting the same amount of leading above ‘30’ dashes (the dashes at the ends of stories) as below them. Some makeup men actually put more leading above than below. As ‘30’ dashes are supposed to end stories, not merely to separate them, and surely not to form parts of following heads, it is advisable to put more leading below than above them. And if body lines of stories are set on slugs of larger point sizes (if the lines themselves are cast leaded), that leading on the slugs themselves should be allowed for when extra leading is placed above ‘30’ dashes. More leading should be used above ‘30’ dashes when body lines are cast solid than when cast leaded. But in either case more leading should be used below the dashes than above.”“Leading” refers to the use of leads (wide bars of metal, originally lead), to add space between lines of print. But more to the point, “dashes” here does not mean the dash or hyphen or minus sign, although these were all called dashes. A dash in this context was like a rule. A rule is, of course, an ornament used in a form that would print a line from end to end. A dash on the other hand would print a line (or some sort of separator) in the middle of the space, and leave the ends blank. I'll put a dash in here.
That's a fairly ornamental dash. Newspapers were more likely to use a simple straight line as a separator between stories. So I thought I had my answer, that the notation simply meant “put a 30 dash here” (which it certainly did) and I assumed that “30” was going to be some sort of typographic measurement. Dashes were certainly measured in ems, and a 6 em dash was a standard thing. Maybe this was a 30 em dash? Nope, newspaper columns were fairly standard at about 13 ems in pica (today we'd call it 12 point) font, so 30 didn't make sense in that context. But dashes were also assigned numbers based on the thickness of the line, and I found 27s and 33s. But no 30.
But then I found this from 1919:
|From Telegraph and Telephone Age, volume 37, November 1, 1919.|
I also found a more detailed article from 1906. It agreed with 30 as a “collect charges” code, and also mentioned other theories, some similar to the blog summary I linked to above, including a person named Thurtee, and claims of civil war origins.
But I was still a doubting Thomas. An 1888 story about “30” and other signals made no mention of the idea of collect charges. So I looked for the evidence that “30” used to mean “collect charges” at some point in time. After much googling, I came up empty. If anything, I found that “pd” and “coll” were common abbreviations used at the end of messages to indicate the charging status. But I did find that there were standard “signals” used in telegraphy, dating back to at least 1854, where I have found two different (but similar) sets of signals. These signals were numeric codes used to transmit simple, common messages like 1 for “Wait”; 2 for “What time do you have?” (which was really important back before we had time zones—which made railroad schedules a nightmare, and which is why the railroads invented time zones for us) and 12 for “Do you understand?”. While all of the signal sets I've seen have similarities, it's also clear that each company used their own set of signals, and some texts specifically call them “private” signals, because there was no standard. By 1862, 30 was a code commonly used, at least in railroad telegraph systems, to mean “Finis”. A very similar set of codes was later adopted as the Phillips Code in 1879, to be used by the Press in their telegraph transmissions.
|From The Christian Union, volume 37, May 24, 1888|
I've also found no evidence that Western Union introduced any set of signals in 1859, however it does seem likely that they had a set of signals in place by then, if only because I've found other older signal sets. And of course the “magnetic” or “electric” telegraph was preceded by semaphore telegraph systems, which also used signals for common messages.
Despite some modern claims, these codes were only used for conversations between telegraph operators, not for substitutions of text within the telegrams. Most companies had rules forbidding this to ensure accurate transmission, and in fact numbers themselves were often transmitted as text, or double transmitted, once as a number and once as text. I found at least one signal which meant “Write the figures into words”.
Another common code was 73, which meant “Best regards”. Some modern sources suggest that this was originally “My love to you” or “love and kisses”. Other sources put 88, or 22 as “love and kisses” (and one even claims this was the “first emoticon”... UGH!). While these usages may have been popular during the ham radio years, they seem unlikely during the early telegraph years, given that they were signals sent between telegraph operators, and not within telegrams. Some stories trace these claims to two sources that I haven't reviewed: “The National Telegraphic Review and Operator's Guide” from April 1857, and the “December Bulletin from the Navy Department Office of the Chief of Naval Operations” from 1934. I did find the July 1853 “National Telegraphic Review”, in which there is an annotation on a poem, where telegraph codes were used in this poem. The annotation translates 73 as “My love to you”, but this may simply be what it best represented in the context of this poem.
|A portion of a poem from The National Telegraphic Review and Operator's Companion, July 1853|
It's clear that numerical codes called “signals” were in wide use very early on, and it's also clear that there was a lot of variation in the codes. “30” became so common that it by 1888 it was worthy of mention in mainstream sources, and also by that time, its origins were too old to clearly piece together. In my opinion it was just an arbitrary choice, like any of the other signals in use. But you never know—history can be a hard thing to pin down.