Here I revisit a topic I have written on several times before, and which furthermore continues the theme of my last column. In the third issue of Parabola Incorporating Function in 2007, I discussed a technique called dimensional analysis and briefly touched on its application by G I Taylor to discover the energy released in the very first atomic blast (the so-called Trinity Test) in 1945: this happened at a time when that figure was still classified as top secret by the US military. I had earlier given a fuller account of the calculation involved in Function (February 1986, with a follow-up in February 1995). I also used this material in a set of course notes at Monash in 1996.
In all these, I was more concerned with the actual Mathematics rather than with the historical detail. Here by contrast, I want to examine that detail more carefully. The story is an intricate one and, as I unravel it, it will emerge that what I wrote earlier, and what is still popular belief, is not entirely accurate. Most of the material that is widely available gives a greatly simplified account of the full situation.