Marin Mersenne and the Telescope
Today, we wouldn't expect to find major advances in the design of telescopes in a book on music. In 1636, Father Marin Mersenne published Harmonie Universelle, a mathematical study of music. It also proposed configurations of mirrors that could be used to produce either telescopic effects or burning mirrors. These configurations were clearly prototypical forms of the Gregorian and Cassegrain telescopes. The image below shows Mersenne's diagrams of his telescopes (image was taken from ).
Full Image (11K)
There is an amusing irony relating to Harmonie Universelle and Lo Specchio. Harmonie Universelle was a book about music but it is important to the history of telescopes. Lo Specchio was a book about mirrors and telescopes but is probably more important to the history of classical mechanics. Lo Specchio contained the first published description of the parabolic nature of projectile motion. Cavalieri's publication of this important concept even caused a short-lived rift in his friendship with Galileo Galilei. Both Galileo Galilei and Thomas Harriot had described projectile motion in private notes but had never published.
Mersenne's work on reflecting telescopes was very advanced. Modern specialists in optics doubt that either he or any of his contemporaries (including Descartes and Galileo) understood the full significance of his work. A full understanding of the advanced nature of Mersenne's work would have to wait until the twentieth century. An indication of this is that the Mersenne telescope, still being produced today, is largely a development of the twentieth century. Mersenne, went further than simply presenting configurations that are used in modern telescopes; his designs featured the strong telephoto effect critical to modern photographic lenses. This all happened 30 years before Newton's telescope . Mersenne actually never did build telescopes to his designs. Oddly, he was dissuaded from building them by Rene Descartes. Descartes felt that reflecting telescopes were impractical. Given the technology of the day, he was probably correct. It would be centuries before reflecting telescopes were competitive with refractors. The mirrors of the time were made of polished metal which tended to tarnish. Also the tolerances for mirrors is four times more critical than for lenses .
A question is raised by Mersenne's work; Why is his work so rarely mentioned in modern histories of the telescope. This includes educational websites and many books. This is not easy to answer. Mersenne was widely considered to be the inventor of the reflecting telescope in the nineteenth century. Several nineteenth century encyclopedias, including the Encyclopedia Americana , identified Mersenne as the inventor of the reflecting telescope. Others, if they did not credit him with the invention of the reflecting telescope, did mention his contribution to its early development. You can find many books from the nineteenth century that reference Mersenne's contribution to the telescope at Google Books. Yet by the middle of the twentieth century Mersenne had largely disappeared from the discussion of the early history of the telescope. In 1943, a survey of the early development of the telescope was published in Isis, a respected journal of the history of science. Mersenne and Cavalieri are not to be found amongst the more than two dozen seventeenth century scientists mentioned. The article begins its discussion of reflecting telescopes with James Gregory in 1663 . The importance given to a historical figure sometimes depends as much on the dominant biases of the day as on their contributions (see Sarton-A Case for Bias).
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