We see a scientist with a Tintin cowlick, experimenting with a bizarre flywheel apparatus. He manages to distil some liquefied electricity, which he pours into a syringe. When he squirts some of this on himself, he runs around in accelerated motion.
He then goes out to try it on other people. One sequence of this movie, with Brighton Beach Pier in the background, was filmed at almost the exact same spot as a scene in Vitagraph's later offering 'Jack Fat and Jim Slim at Coney Island' (1910). The scientist spots some boaters trying to rescue a drowning bather: he squirts some liquid electricity into the proceedings, and everyone moves at accelerated speed.
The trick is done, of course, by undercranking: slowing the camera to lengthen the interval between frames ... so that, when the film is projected at normal speed, the action is accelerated. It's unfortunate that the makers of 'Liquid Electricity' undercrank a shot of the ocean: one of the lessons in Movie-making 101 is never to undercrank a shot of water, fire or smoke: the results will always look unnatural.
Unfortunate for a different reason is a scene here in which the scientist encounters a Negro couple, played by a white man and woman in dark make-up. The husband lackadaisically whitewashes a wall: the scientist gives him a squirt of liquid electricity, and the black man works at superhuman speed while his black wife watches approvingly.
Several scenes in this film are quite funny, but unfortunately the movie just ENDS, with no real punchline. I thought that perhaps a scene was missing from the end of the print, but apparently in 1907 the people at Vitagraph Studios were still learning how to tell a story with a punchline.
I must correct the (normally very perceptive) IMDb reviewer Bob Lipton, who theorises that a rear-projection process is used in one sequence of this 1907 film, when the scientist moves at normal speed while one of his test subjects moves super-fast. In order to shoot a rear-projection sequence for this movie, the Vitagraph technicians would have been required to synchronise the gate mechanisms in the camera and the projector ... very difficult to do in 1907! In fact, the trick here is something simpler (yet more impressive) than rear projection. If you watch the scientist closely in this sequence, you'll see that his movements in this scene -- and ONLY in this scene -- are very precise and deliberate, almost choreographed. It's obvious that the actor playing the scientist is actually moving very slowly, while the actor playing his test subject is moving at normal speed. Both actors are in the same set-up, with only one camera exposure. When the undercranked film is projected at normal speed, the test subject's movements are accelerated, while the scientist is moving normally! This is very well done, and I regret that the film's credits don't identify the actor who plays the scientist. I'll rate this delightful movie 8 out of 10.