Charles Petzold

How the Earth Got Old

December 19, 2019
Sayreville, New Jersey

I’m calling this document a Preliminary Draft of Chapter 4 of Computer of the Tides because it’s nowhere close to the final version, and I can prove it mathematically: I intend for Computer of the Tides to come at about 350 pages spread over 10 chapters, which means that if the book is well balanced among the chapters, each chapter will be about 35 pages. This Preliminary Draft is about 2½ times that length.

Therefore, huge chunks of this document need to be savagely hacked off before it becomes part of the book, and I’ll feel a lot better doing that if I know that this “complete” version will still exist. Think of it as the Director’s Cut.

My wife Deirdre Sinnott courageously read an earlier draft and supplied some great fixes and feedback that I’ve mostly incorporated. Thank you! However, this document has not been touched by those angels known as copy editors, so it’s likely peppered with many little slips and flubs of language and spelling. Just today I discovered I referred to Prince Albert once as Prince Alfred. Yikes!

Computer of the Tides is my book-in-progress about the tide-predicting machine invented by Scottish physicist William Thomson (Lord Kelvin). I will show in this book that the tide-predicting machine arose out of an age-of-the-earth controversy initiated by Thomson in 1862 shortly after the publication of Charles Darwin’s Origin of the Species. Thomson’s intent was to demonstrate that the earth was not old enough for natural selection to have occurred. Several aspects of that story require knowledge of the earlier pre-Darwin age-of-the-earth controversy. That’s the reason for Chapter 4.

Chapter 4 covers the turbulent history of how the earth increased in age from about 6,000 years to millions of years. The chapter is restricted to the period between about 1750 and 1850, and largely focuses on British and French geologists and natural philosophers. Within the history of science, this is probably as important a story as the Copernican Revolution, but it is not as well known to the general public. The chapter also touches upon topics that relate in other ways to the “crisis of faith” during the Victorian era, which is necessary to understand William Thomson’s motives.

It’s a big story, and as I worked on this chapter I peeled off several false starts, deeper dives, and digressions. For many years I thought that I’d begin the chapter with poet William Cowper and 4½ lines of his epic poem The Task. That work became the essay ”William Cowper and the Age of the Earth”. A phrase from Cowper's verse remains as the title of the chapter.

At one time I had a longer discussion of the late 17th century cosmogonies of Thomas Burnet, William Whiston, and John Woodward. I reduced that to a paragraph and the longer material became the blog entry ”Clever Cosmogonies of the 17th Century”. While researching Thomas Burnet, I got distracted by the origins of the verse “All the Books of Moses / Were nothing but supposes”. Another digression became the blog entry ”Biblical Chronology and the Encyclopædia Britannica”.

At one time I had a great idea to go straight from Haydn’s oratorio The Creation (which is how Chapter 4 still begins) to Laplace’s Nebular Hypothesis because I had it on good authority that Haydn was influenced by a visit to see William Herschel and his telescope where he learned all about Laplace’s theory. That dead end inspired the blog entry ”Haydn and Herschel in the Claire de Lune”.

Even with all that stuff removed from Chapter 4, it’s still way too long. In recent years, access to primary sources has become much easier, largely as a result of Google Books and similar sources. I’ve enjoyed including extended quotations from the major players in this story. I feel that the texture of their own writings gives the reader a more accurate flavor of the debate and controversies. I suspect that one way this chapter will be shortened is by summarizing in my own boringly succinct words the gloriously long sentences of those quotations.

But I'm not yet ready to do that. Computer of the Tides is nowhere close to the point where I can even think about publication.

If you have any comments or corrections, let me know at