Freedom of Science

These are the days of the week Cavendish made his 17 observations.¹

Monday: 0
Tuesday: 1
Wednesday: 5
Thursday: 6
Friday: 3
Saturday: 0
Sunday: 3

More info on experiment dates.

We can guess why Cavendish did not experiment on Mondays. Cavendish was a recluse and his only social affair was going to Royal Society meetings and dinners. He read his paper reporting the experiment to the Royal Society on Monday, June 21, 1798. Another record that I have is when Cavendish took Francis Wollaston to the Royal Society as a guest on Monday Dec. 8, 1768. So, circumstantial evidence suggests that the Royal Society meetings were held on Mondays and one could find Cavendish there. No time for experimenting on Mondays.

What about Saturdays? I don’t know. Why Thursday was his favorite day for experimenting? I don’t know.

There were 293 days from August 5, 1797 to May 30, 1798.

I find it strange that Cavendish found time in only 17 of those 293 days to make measurements.

He was busy on August and September 1797 and then he gave up observing for 6 months. That’s a big gap. I am worried that the properties of the copper wire carrying close to 2 kg load would vary in 6 months. The distance between weights would vary. We know that Cavendish only gave an approximate value of 8.85 inches for the distance between the weights. Note that Cavendish is measuring an attraction, as he put it, “not more than 1/50,000,000 of the weight” but leaves the pendulum in a shed for 6 months. The apparatus is so sensitive that if a spider happened to weave his net between pendulum arm and the mahogany box during that 6 months hiatus our understanding of the universe would be in need of modification since the value of G as we know it today would have been so different.

There is no evidence that Cavendish calibrated the instrument more than once.

Last measurement was on May 30, 1798 and Cavendish read the paper on June 21, 1798, less than a month later. Given the difficulty of computing the measurements by hand without computers I would say that Cavendish has been working on the paper more than a month. He was 67 years old when he did the experiment.

1. Courtesy of Weekday Calculator [↩]

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