On March 25, 1925, John Logie Baird set up an unusual contraption in the Selfridges department store in London. It was a gimmick for attracting shoppers, casting a silhouette of a ventriloquist's dummy from across the room. A few months later — on January 26, 1926 — he demonstrated another version that's recognized as the first public demonstration of a mechanical TV.

Mechanical televisions came before the electronic televisions we have today — they were an early way to transmit images without film, and they paved the way for the TVs we use now.

"It was a wonderment," says Gary Edgerton, author of The Columbia History of American Television. "I imagine a lot of people who showed up at Selfridges that day had never thought of television." When Baird sent some blurry silhouettes across a department store, he made history.

The creator of the mechanical TV was a "mad inventor"

Baird, the inventor of the mechanical TV, was a Scotsman with an entrepreneurial spark. He was constantly trying out crazy ideas, like a rustless glass razor and inflatable shoes. He was nuts in the best possible way.

"He in some way looks like the mad inventor," Edgerton says. In a typical story, as a city engineer, Baird accidentally blew out all the power in Glasgow. After that, he proposed inventions like the "Baird undersock," a second sock you'd wear ... under your socks.

At first glance, his mechanical television might have seemed like just another crazy idea in a long list of failures. His first device was built from a hodgepodge of materials that included an old tea chest, an empty biscuit box, and some cardboard discs. But it was able to broadcast a few silhouettes and the outline of a paper mask. And with Baird's first presentation at Selfridges, he made history.

How the first mechanical television actually worked

The device relied on Nipkow discs — spinning discs with various holes in them. As the disc spun, the transmitter shone light through its holes, hitting the object being "filmed." That light then hit a sensor that captured the pattern and transmitted an electrical signal. The signal traveled via radio waves to a receiver with its own Nipkow disc rotating in sync with the original, allowing the initial image to be reproduced.

The original images were low-resolution and blurry. Television resolution is measured in lines, and in the beginning, the device could only scan as many lines as there were holes in the disc. A typical HDTV that's 1080p has 1,080 lines — Baird's device only had 30. Nipkow discs were occasionally dangerous, too — sometimes they spun so fast they flew off and hit things. But they worked.

Baird's mechanical TV was ingenious — but lost out to electronic TV

The haunting image above was one of the first to be transmitted using TV, but the clarity quickly improved. Later that same year, Baird took his next big step forward. In October 1925, he broadcast the face of a ventriloquist dummy named Stookie Bill. From there, he moved on to human faces.

Mechanical TV progressed in fits and spurts, but Baird did manage to improve his device. As described in R.W. Burns's Television: An International History of the Formative Years, a spotlight system helped Baird focus the lights in the device so that it was easier to photograph objects and produce a better "scan." In 1927, Baird sent a signal hundreds of miles over telephone line. In 1928, he made a color transmission by using color light sources and color filters. He also added lines, and eventually tried a 120-line mechanical system.

"it's a shared invention that all these folks played a part in"

But mechanical TVs lost out to the electronic television, invented by Philo Farnsworth in 1927 and demonstrated in 1928. Electronic signals could be more easily captured and reproduced, and they could appear with superior fidelity and resolution. Baird moved on to electronic television as well, along with other new experimental products.

That said, historians recognize Baird's role in the early development of TV. "When I think of John Logie Baird, his biggest contribution was making the public aware of television," Edgerton says. "Philo Farnsworth probably contributed more than anybody, but truth be told, it's a shared invention that all these folks played a part in." Together, the iterative process "spurs and inspires other people to continue and compete."

That's why Baird is best remembered for what he accomplished in a department store and, later on, with a ventriloquist's dummy. Mechanical television helped push television forward and probably hastened the development of electronic TV. As Gordon Selfridge said of his department store hire, "unquestionably the present experimental apparatus can be ... perfected and refined." And it was, thanks in part to the genius of a former socks salesman who had a good idea.

Updated: The anniversary depends on how you determine the milestone — last year, we celebrated the 90th anniversary of that televised silhouette at Selfridges, and today marks the 90th anniversary of the first public demonstration of a more recognizable televised image. Whichever day you mark, it was a significant one in television history.