In Fisher's previous book 'How to dunk a doughnut' he looked at the science of things in everyday life. The emphasis in 'Weighing the soul' is a bit different, here he looks at some historical episodes which illustrate how different viewpoints have clashed and how one of them has come to be accepted. The historical viewpoint may mean that it has a less general apppeal than his previous book. For instance it might not be so appreciated by school-age readers - they might like some of the dangerous chemical experiments he did when he was child, but I'm not sure their parents would approve. However, it is still very readable, and those who do read it will be richly rewarded with an insight into the way science actually works.
The title of the book relates to the first chapter which examines experiments which seemed to show that the soul had substance. These weren't crackpot experiments, they were carefully carried out, and Fisher explains how this weird result might have been obtained. There is also a chapter on how Thomas Young's demonstration that light was a wave was suppressed for many years by scientists who took Issac Newton's word as law.
The last quarter of the book comprises notes to the text, which does seem a bit excessive - it moves it away from popular nature of his previous work, although it's very useful if you want to follow up on some of the ideas.