A woman bought a vintage dress at an antique store. It had a secret pocket with a mysterious note

(CNN) — The Victorian dress in the Maine antique mall was unlike anything Sara Rivers Cofield had seen before.

Its fitted bodice, puffy bustle and lace cuffs reflected a bygone era. As a vintage costume collector, Rivers Cofield recognized it as a dress from the 1880s — but despite its age, its delicate embroidery, bronze silk and metallic buttons appeared intact.

She haggled the price down to $100 from $125 as she wondered where she’d store the two-piece garment. The price was higher than she usually pays as an archaeologist who collects antique costumes and purses for fun. But it was the holiday season, so she splurged.

Rivers Cofield had no idea that the dress she bought in December 2013 would unravel a mystery a decade later. Inside a secret pocket tucked under the bustle were two crumpled sheets of paper with lists of seemingly random words and places:

Bismark, omit, leafage, buck, bank

Calgary, Cuba, unguard, confute, duck, Fagan

Notes on the margin of the papers appeared to depict time. A tag stitched into the dress had a handwritten name: Bennett.

Rivers Cofield was baffled, she told CNN. The words were cryptic. What did they mean, and why did Bennett need a “super secret hidey-hole,” in Rivers Cofield’s words, to stash them? The buttons alone portrayed a forlorn Ophelia from Shakespeare’s “Hamlet,” and were worth more than she’d paid for the dress, she said.

In February 2014, she posted a blog about the dress, which she’d nicknamed Bennett’s Bronze Bustle. “What the…?,” she wrote. “I’m putting it up here in case there’s some decoding prodigy out there looking for a project.” She included photos of the dress and the papers.

Online sleuths took up the case – but without success

Rivers Cofield, an archeological curator who lives in Chesapeake Beach, Maryland, had bought the dress while visiting her mother in Searsport, Maine. She didn’t think much about it after her blog post.

But unbeknownst to her, curious amateur sleuths were working to solve the mystery. They dubbed it the “silk dress cryptogram” and floated conspiracy theories about the words. Some speculated that Bennett was a spy using coded words to communicate.

In 2017, one blogger added the note to his list of the Top 50 unsolved encrypted messages and floated more theories. Was it a cryptic love note? Dress measurements? Civil War codes?

Rivers Cofield quickly dismissed any interpretation linked to the Civil War. She has studied 1880s catalogues from department store chain Bloomingdale’s, and had no doubt the dress was from that era. By then, the war had been over for about 20 years.

Others speculated it was a form of communication related to the telegraph, a new way of sending quick notes launched in the United States in the 1800s, which charged senders a fee based on the number of words in a message.

“I had kind of abandoned the blog at that point,” Rivers Cofield said.

“Every once in a while I would see that a comment was posted or that some other codebreaker would email me and be like, ‘Hey, I’m still interested in this,’ but nobody ever solved it.”

But then a Canadian researcher cracked the code

Wayne Chan, a researcher at the University of Manitoba in Canada, stumbled across the code online in summer 2018. He told CNN he looked at 170 code books and none of them matched the message.

“I worked on it for a few months, but didn’t get anywhere with it. I set it aside and didn’t look at it again.” Chan said.

Chan, who solves codes as a hobby, then began researching the telegraph era, including the weather codes used in North America at the time. And early last year, he had a breakthrough.

He discovered the coded messages were in fact, a weather report. And they were not encrypted for secrecy but because the code allowed forecasters to shorten detailed weather reports into a few words, Chan said.

In the era of the telegraph, such shorthand was cheaper than sending a big batch of words and temperature readings. Each word represented meteorological variables such as temperature, wind speed and barometric pressure at a specific location and time of day.

For example, the line “Bismark Omit leafage buck bank” contains surprisingly specific details. “Bismark” meant it was recorded at Bismarck station in what is now North Dakota. “Omit” meant the air temperature was 56 degrees and the barometric pressure was 0.08 inches of mercury. “Leafage” referred to a dew point of 32 degrees Fahrenheit observed at 10 p.m. “Buck” indicated there was no precipitation, while “bank” meant a wind velocity of 12 mph and a clear sunset.

All weather stations were required to send their reports by telegraph to a central office in Washington, DC, Chan said.

Chan discovered that the encoded messages used a 19th-century telegraphic weather code used by the Army Corps, which was the national weather service for the US during the late 1800s. For example, a phrase like the “The crew are all drunk” would be shortened with a codeword such as “crimping,” he noted

“This particular code was not meant for secrecy at all. Telegraphic codes were used for two main reasons: secrecy and economy,” Chan told CNN. “The weather code was for the latter. Because you were charged by the word in a telegram, they wanted to shorten or compress a weather report into as few words as possible to save on costs.”

Chan said he’s not sure how the words were picked. There was a weather codebook that meteorologists consulted to understand the meaning behind unfamiliar words. And with time, they learned the codewords without the need to consult the codebook, he said.

“The words were arranged so that particular consonant-vowel pairs represented specific numerical values,” Chan said. “It was really a very complex code, even though the intent was not for secrecy.”

He was able to pinpoint the weather report’s exact day

Chan wrote an academic paper explaining the topic. He also emailed Rivers Cofield, who did not know that online sleuths were still working to decipher the codes.

Rivers Cofield said she was stunned by the revelation, but not surprised.

“I’m an archaeologist for a living, so I do a lot of research into the past,” she said. “I’ve long since come to terms with the fact that not every artifact or every document is going to reveal all of its secrets.”

As part of Chan’s research, the National Oceanic and Atmospheric Administration provided old weather maps that helped him determine the precise date of the weather observations in the coded note: May 27, 1888.

Rivers Cofield said one of the biggest takeaways from the discovery has been realizing that people had no immediate way of knowing what weather was coming in the 1880s.

“It never occurred to me that the telegram would have been what unlocks that for people. … Because (now) we’re all so used to our weather apps,” she said.

It’s still unclear who Bennett was and why she had weather codes stashed in a secret pocket.

But for now, Chan and Rivers Cofield are just glad they’ve unraveled the biggest piece of the dress’s mystery.