Interesting, though, for DIY, I was expecting him to do it the way Linde did, back in 1894, that being:<p><pre><code> Compress some dry air.
This will heat it up, so cool it down.
Return it to atmospheric pressure.
</code></pre>
While expanding, it, of course, gets even colder still, and condenses. Liquid nitrogen is old tech, older than you might think.