Assembly complete ...

Everything is connected, and after some tweaks, it looks like this:

Even though this setup is only 8 nodes, the amount of hardware involved is pretty significant when you put it all together.  I expected that there would be at least one or two things that didn't work, and that came to be.  As it turns out, one of the power supplies (cell phone chargers) was DOA, and Pi card number 7 would never fully boot.  I tried replacing the SD card and the network cable, but the system either hangs, or goes into an infinite loop on first boot.  Sometimes I could get into the raspi-config tool, but it would never complete before a problem occurred, and it never failed at the same place every time.  I don't know why this happens, I could have damaged the card as I was mounting it, who knows.  It's just the way things go, and I'll have to replace it as I move forward.

Once the physical configuration was complete, I went to my router, and assigned fixed IP addresses for all of the nodes.  This involved finding the MAC address of each card (see the HWAddr field):

pi@raspberrypi ~ $ sudo ifconfig
eth0      Link encap:Ethernet  HWaddr b8:27:eb:1e:12:7d 
          inet addr:192.168.1.151  Bcast:192.168.1.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1664 errors:0 dropped:0 overruns:0 frame:0
          TX packets:281 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:154134 (150.5 KiB)  TX bytes:27682 (27.0 KiB)

There should be a section of the admin interface on your router where you can choose an IP address and assign it to each of these MAC addresses.  Once the IP addresses are fixed, it's a relatively easy task to build a few tools to do housekeeping things like ping all of the nodes, or tell them all to shut down.  I've been able to reach all of these nodes using SSH, and expect that I'll build my tools around this.  There is probably someone out there who has done this before, but I'll do my own version, just to make it work the way I want.  I plan to enlist the aid of my able sidekick and son Neil to put a web interface on these tools once I have them working from the command line.

The next step is to move forward with the configuration as professor Cox describes - building the Message Passage Interface (MPI) for distributing work throughout the network.  This will be interesting to see work.