Date: Tue, 25 Aug 98 08:11:25 -0400 From: Steve Detweiler To: James Fry Subject: Re: Newtonian black holes Jim, The Reverend John Michell in a letter to his good friend Henry Cavendish that was published in Transactions of the Royal Society in 1784. Here is an excerpt of a summary I made in a letter to a friend--I think its amusing! The reference is "On the Means of discovering the Distance, Magnitude, etc. of the Fixed Stars, in consequence of the Diminution of the Velocity of their Light, in case such a Diminution should be found to take place in any of them, and such other Data should be procured from Observations, as would be farther necessary for that Purpose", by the Rev. John Michell, B.D.F.R.S., in a letter to Henry Cavendish, Esq. F.R.S. and A.S., Philosophical Transactions of the Royal Society of London, Vol. LXXIV, 35-57 (1784). We sure don't title papers the way they used to. I was at Yale when I found out about this article, so I called up their rare books library and was informed that 1784 really wasn't so long ago and that the volume I wanted was on the stacks in the main library. I just checked it out, they had to glue in a new due date sticker in back, and I had it on my desk for six months. Michell's idea is to determine the distance to the stars by measuring the speed of light from the stars--the further away the star is, the slower the light would be moving. He conceded that there would need to be improvement in prism quality for this to be possible, but he thought it was within reach. Its an interesting paper, the arguments are all geometrical, where there should be an equation he writes it out long hand, all the s's look like f's, and its fun to read. Somewhere in the middle of the paper (paragraph 16), he notes that if a star were of the same density as the sun but with a radius 500 times larger, then the light would be pulled back to star and not escape. He even surmises that we might be able to detect such an object if it were in a binary system and we observed the motion of the companion. So we should have celebrated the Black Hole Bicentennial back in 1984! And Michell was an interesting fellow. He wrote 4 papers that I know about, and I think these are in chronological order. In one paper (1760), he notes a correspondence between volcanos and fault lines in the earth's crust and first suggested that earthquakes might be caused by masses of rocks shifting beneath the earth's surface. In another, Michell (1767) estimates that if the stars were just scattered randomly on the celestial sphere then the probability that the Pleiades would be grouped together in the sky is 1 part in 500,000. So he concluded that the Pleiades must be a stellar system in its own right---this is the first known application of statistics to astronomy. In a third paper, he devised a torsion balance and used it to measure the 1/r^2 dependence of the force between magnetic poles. His fourth paper has the black hole reference. After that work, he started a project to modify his magnetic-force torsion balance to measure the force of gravity between two masses in the laboratory. Unfortunately, he died in the middle of the project. But his good friend, Henry Cavendish, stepped in, made important improvements and completed the experiment! In his own paper, Cavendish gives a footnote reference to Michell.