What the Heck Is a Crookes Tube? (Lovecraft story talk)

Image of Crookes tube in operation, from D-Kuru, CC BY-SA 2.0 AT, via Wikimedia Commons

I didn't know until yesterday that August 20th was H. P. Lovecraft's birthday! It seemed like a worthy time to go through a couple of his stories, so I read two of them last night: Under the Pyramids (written with Harry Houdini, of all people), and The Shunned House.

The Shunned House is one of my favorites of Lovecraft's stories. Not too long, but long enough to develop some characters and build some tension. The slow build up of evidence, starting from the old owners of the house, and stepping forward in time until a lucky glance back to an even earlier era leads to the primary conclusion of the main character, and the terrifying adventure he undertakes.

One of the things I noticed on this readthrough of the story was his mention of having a couple of Crookes tubes to shoot radiation at the monstrous thing when it appeared, if material force proved ineffective.

This time, I finally went around and looked up what exactly a Crookes tube was: it's a precursor to modern cathode-ray tubes, like the one in your old tube TV!

"Hot" cathode-ray tubes have a piece of metal in there that is electrically heated such that it emits electrons (cathode-rays), which are then accelerated toward the anode by the electrical potential difference between the two. Hot cathode-ray tubes have a warm-up time and are often indirectly heated, so that alternating current (AC) can be used for heating, but direct current (DC) can be used for accelerating the electrons.

A hot-cathode filament. Created by Deglr6328, uploaded by Superclemente, CC BY-SA 3.0, via Wikimedia Commons

Remember how TVs used to have a warm-up time? Cold cathode-ray tubes don't have a warm-up time because there's nothing to heat.

A Crookes tube (or Crookes-Hittorf tube) is a cold cathode tube that uses a high DC voltage between the cathode and anode to excite low pressure gas molecules into liberating electrons. A Crookes tube needs imperfect vacuum in order to operate.

Some of the electrons accelerated inside the Crookes tube end up going so fast that they fly right by the anode and out the other end of the tube! Thus, a Crookes tube is basically a cannon for high-energy electrons!

A Crookes tube diagram from Wikipedia (public domain). The cross-shaped shadow in the outputted electron beam is kinda cool, too, and appropriate for killing vampires.

High-energy electrons are equivalent to beta radiation in modern parlance (except beta radiation also includes positron emissions in some cases).

So, basically, that's what Lovecraft's character was going to try to use against the evil presence in the story: A high-powered cross-shaped electron beam!