Feeling very gravitational today!

I enjoy reading aloud. I've read dozens of books aloud to my wife, Janet. Right now I'm reading Timothy Ferris' book "Coming of Age in the Milky Way." It's the story of how humanity figured out just how big the universe is.

The chapter I read last night was on Newton, the discoverer of the universal gravitational constant. The book describes in a very entertaining way what kind of loony character Newton was. But it didn't describe how Newton figured out that constant, G.

So I looked up the article on gravitation in the 1995 Encyclopaedia Britannica. Sure enough, there was the explanation for how Newton figured out G. He made a guess at the density of the earth (turned out to be just about dead-on) and thus calculated the mass of the earth. That led him to a figure for G: 6.608 x 10^-11 meters cubed per second squared per kilogram. OK! I now knew how G had been derived by Newton.

But I saw that the units used for G in the Britannica looked funny. Not only that, a table at the end of the article showed the correct representation of units.

I checked the Britannica online version of the article and found that the error has been perpetuated. So I wrote the following letter:

Dear Sirs,

There is an error in the article on Gravitation. I first noted it today in the 1995 print edition of the Encyclopaedia. It still appears in the online edition.

In the online article, http://www.britannica.com/eb/article-61466, the phrase immediately following formula (7) reads:

which numerically comes close to the accepted value of 6.6726 x 10^-11 m^3 x s^-2/kg^-1

I've used the caret (^) to indicate a power. The phrase SHOULD read:

which numerically comes close to the accepted value of 6.6726 x 10^-11 m^3 x s^-2 x kg^-1

which jives with the description of the formula found in the table: http://www.britannica.com/eb/table?tocId=9115984:

G (in units of 10^11 cubic metres per second squared per kilogram)

Sincerely,

Steve Erbach
Neenah, WI

I then noticed a second error. That prompted this letter:

Dear Sirs,

After sending my first message this morning, I noticed a second error in the Britannica online article on Gravitation. In article http://www.britannica.com/eb/table?tocId=9115984, the phrase should be changed FROM:

G (in units of 10^11 cubic metres per second squared per kilogram)

TO:

G (in units of 10^-11 cubic metres per second squared per kilogram)

Sincerely, etc.

My 0.03 seconds in the sun...