Just as the thread on post on Drilling was winding down two weeks ago, horizonstar posted a comment about the tools that Potter Drilling is developing for geothermal drilling, with $4 million worth of help from Google. The comment takes you to a Grist post, from which I am now going to pinch the top illustration.

Now (if you will forgive the vanity) I will add a picture from my doctorate, and an experiment that I carried out in 1967.

Now if you look at the two holes you might think that the top hole is the better, and more efficiently drilled. This post is going to try and explain why in fact it is the bottom hole that is better.