In my review of The Accidental Scientist, I raved about how much I enjoyed the book, but that I had reservations about the way the author's style, no matter how entertaining it was. Turns out those reservations are well founded. In When the Earth was Flat, his penchant for pedantry and generalisations are so broad as to be misleading.
The book is broken up into chapters that each cover a "scientific" theory believed to be fact at some point in history. Flat Earth, Hollow Earth, Phrenology, Hysteria, etc. Each includes a basic description of the belief and the effect it had on humanity both at the time, and sometimes, up to the present day.
Most of these are, I believe, pretty well researched, and they are well written; I learned a lot, and while I won't take any of it as gospel truth without some additional fact-checking, I have a level of confidence that the book is generally sound. I'm agog at the implications of certain medical "advancements" of the 1920's and their possible links to HIV.
But where he loses ground is in his breakout boxes that list "Popular Scientific Ideas Debunked". These are just bullet point statements refuting what are widely believed to be scientific facts. Most of them are gimmes; anyone who has read any similar book would recognise them as myths rather than facts. But a number of them are - while factually correct if your pedantic - irresponsibly phrased. For example:
Heat does not rise but disperses itself equally and evenly throughout its environment.
Yes, but no. Or not immediately. A gas that is heated up will have less mass and more volume, and therefore will rise up through a colder gas until the heat is dispersed equally and evenly throughout. That's how weather works. Anyone who has ever seen a thunderstorm form, especially a microcell, has seen the hotter air rising up through the atmosphere (really, the colder air is sinking, but anyway...). This is nature's way of re-establishing equilibrium, or as close as it can get before the sun comes back out.
The same applies to water (until water hits the freezing point); cold water is denser than warm water, so the colder water sinks to the bottom and the warmer water rises to the top, until the temperature is equal throughout. We're lucky that that equilibrium is never achieved in our oceans, else life on Earth would become rather untenable.
So while his statement is factual, it's oversimplified to the point of being wrong, and since he does not trouble himself, or the reader, to explain beyond these casual, throw-way refutations, I find them incredibly irresponsible. This is why there are so many ignorant people who cannot see that they are ignorant: they read things like this and think themselves informed... and then run for political office. Simplification, like everything else in life, should only be practiced in moderation.
To sum up, it's not a bad read; I believe 90% of the information can be relied upon and for the reader who is new to science or just enjoys fun facts, this is entertainingly written. But, as in any non-fiction book, the reader should be cautious of single sentence statements of facts. It's rarely that simple.