Skip to main content

Plan 28

I've created a domain specially for my investigations of the possibility of building an Analytical Engine to (close to) Babbage's plans. It's called Plan 28. It references the fact that Babbage's most detailed plans of the Analytical Engine are in the form of two plans numbered 28 and 28a and stored in the Science Museum in London.

These plans depict a machine with a mill (the CPU, capable of doing addition, subtraction, multiplication and division), a store (the memory), and the barrels (microcode for the mill operations). It's the closest thing to a computer as we know it (although the program and the data are stored separately and programs have no way of accessing anything other than fixed memory locations: i.e. there are no references or pointers).

If you are following along and want some reading then go with the following:

  1. The Difference Engine by Doron Swade. It's an easy, quick read introduction to Babbage, the Engines and the reconstruction of Difference Engine No. 2. The latter reconstruction demonstrates that the construction techniques available to Babbage were sufficient and would have enabled the construction of the machine. The reconstruction cost £250,000 in the late 1980s.

  2. The Little Engines that Could've. This is a PhD thesis by Bruce Collier and goes into a lot of detail about the operation of Babbage's engine. I turned those web pages into PDF and had it bound so I could sit and read it. The PDF is here.

  3. Charles Babbage's Analytical Engine, 1838. IEEE article by the man who probably understood Babbage's Engines better than anyone in the 20th century, Allan Bromley. This article introduces the state of the machine as of 1838.

  4. Babbage's Analytical Engine Plans 28 and 28a-The Programmer's Interface. Also by Allan Bromley this paper covers the Analytical Engine in 1847 when Babbage stopped working on it. In particular, it details the instruction set that would have been available to the programmer.

  5. The Evolution of Babbage's Calculating Engines. More historical context from Allan Bromley putting the design of the Analytical Engine in context with the Difference Engines and modern computers.

  6. Babbage's Analytical Engine Babbage's son, Major-General H. P. Babbage, describes his construction of part of the Analytical Engine.

  7. The Analytical Engine Also by Babbage's son, this long paper describes the operation of the Analytical Engine as he understood it.

  8. Of The Analytical Engine Charles Babbage's own description of the Analytical Engine from his autobiography.

  9. Sketch of the Analytical Engine The famous paper translated by Ada Lovelace on which much of her fame rests.

And as a bonus, here are some pictures I took at the weekend in the Science Museum in London.

The first shows a trial portion of the Difference Engine:

Here are some punched cards prepared by Babbage that would have been used for programming the Analytical Engine:

And here's the trial section of the Analytical Engine that Babbage built:

And, finally, the mill of the Analyical Engine. This was built by Babbage's son after his father's death.


Unknown said…
I was thinking a while back about whether you could crowdsource the digitisation of the plans. That is, first scan them in and put them on the web, and then write a web app in which people could trace them into a 3d model.

After that, you would need a physics engine for people to try sticking the cogs and things together...

Popular posts from this blog

Your last name contains invalid characters

My last name is "Graham-Cumming". But here's a typical form response when I enter it:

Does the web site have any idea how rude it is to claim that my last name contains invalid characters? Clearly not. What they actually meant is: our web site will not accept that hyphen in your last name. But do they say that? No, of course not. They decide to shove in my face the claim that there's something wrong with my name.

There's nothing wrong with my name, just as there's nothing wrong with someone whose first name is Jean-Marie, or someone whose last name is O'Reilly.

What is wrong is that way this is being handled. If the system can't cope with non-letters and spaces it needs to say that. How about the following error message:

Our system is unable to process last names that contain non-letters, please replace them with spaces.

Don't blame me for having a last name that your system doesn't like, whose fault is that? Saying "Your last name …

All the symmetrical watch faces (and code to generate them)

If you ever look at pictures of clocks and watches in advertising they are set to roughly 10:10 which is meant to be the most attractive (smiling!) position for the hands. They are actually set to 10:09.14 if the hands are truly symmetrical. CC BY 2.0image by Shinji
I wanted to know what all the possible symmetrical watch faces are and so I wrote some code using Processing. Here's the output (there's one watch face missing, 00:00 or 12:00, because it's very boring):

The key to writing this is to figure out the relationship between the hour and minute hands when the watch face is symmetrical. In an hour the minute hand moves through 360° and the hour hand moves through 30° (12 hours are shown on the watch face and 360/12 = 30).
The core loop inside the program is this:   for (int h = 0; h <= 12; h++) {
    float m = (360-30*float(h))*2/13;
    int s = round(60*(m-floor(m)));
    int col = h%6;
    int row = floor(h/6);
    draw_clock((r+f)*(2*col+1), (r+f)*(row*2+1), r, h, floor(m…

Importing an existing SSL key/certificate pair into a Java keystore

I'm writing this blog post in case anyone else has to Google that. In Java 6 keytool has been improved so that it now becomes possible to import an existing key and certificate (say one you generated outside of the Java world) into a keystore.

You need: Java 6 and openssl.

1. Suppose you have a certificate and key in PEM format. The key is named host.key and the certificate host.crt.

2. The first step is to convert them into a single PKCS12 file using the command: openssl pkcs12 -export -in host.crt -inkey host.key > host.p12. You will be asked for various passwords (the password to access the key (if set) and then the password for the PKCS12 file being created).

3. Then import the PKCS12 file into a keystore using the command: keytool -importkeystore -srckeystore host.p12 -destkeystore host.jks -srcstoretype pkcs12. You now have a keystore named host.jks containing the certificate/key you need.

For the sake of completeness here's the output of a full session I performe…