Born Spitalsfield, (London), England, 10 June 1706
The achievement for which the optician John Dollond is best remembered is his invention of the achromatic refracting telescope. Dollond’s father, Jean, was an immigrant from Normandy. John privately studied Latin, Greek, anatomy, theology, algebra, geometry, optics, and astronomy. He married Elizabeth Sommelier, who bore him two sons (Peter and John) and three daughters (Susan, Sarah, and one with name unknown).
At the age of 46, John joined his eldest son Peter Dollond who had set up shop as an optician. By the following year, John had made two new devices that could be used with telescopes. The first was an ocular with additional lenses that led to a reduction in the spherical and chromatic aberration. The second was a divided object glass micrometer, also called a heliometer. In this device, the objective of a telescope is divided into two halves, one or both of which could be driven laterally, thus giving a double image. By measuring the relative distance the lenses moved, for example, to bring the images of two stars together, one could calculate their angular separation. The heliometer was extensively used to measure the seasonal variations in the angular diameter of the Sun and also was applied to the measurement of the diameter of planets, the spheroidal shapes of planets, and the elongations of Jupiter’s satellites.
Isaac Newton had noticed that the various colors comprising white light were not all brought to a focus by a lens at the same place, resulting in a blurred image with colored borders. Furthermore, his experiments seemed to indicate that there was no way to avoid that problem except to use a reflecting telescope. But after Newton’s pronouncement was brought into question by Leonhard Euler and Samuel Klingenstierna, Dollond performed experiments with prisms of various types, which indicated that it was indeed possible to make a lens corrected for chromatic aberration by combining a converging lens of crown glass with a diverging lens of flint glass. For this achievement, he was awarded the Royal Society’s Copley Medal. Although there was a controversy over his priority in the invention, he was granted a patent and began producing high-quality achromatic telescopes.
Dollond became optician to King George III. Instruments from the Dollond shop went to astronomical observatories all over the world and were produced long after his death.
- Kelly, John (1804). “The Life of John Dollond, F. R.S., Inventor of the Achromatic Telescope.” Philosophical Magazine18: 47–52.Google Scholar
- — (1808). The Life of John Dollond, F.R.S., Inventor of the Achromatic Telescope. 3rd ed. London: W. M. Thiselton.Google Scholar
- King, Henry C. (1979). The History of the Telescope. New York: Dover.Google Scholar
- Reed, George (May 1984). “Dollond vs. Hall: Through an Achromatic Lens.” Griffith Observer: 2–11.Google Scholar
- Rudd, M. Eugene, Duane H. Jaecks, Rolf Willach, Richard Sorrenson, and Peter Abrahams (2000). “New Light on an Old Question: Who Invented the Achromatic Telescope?” Journal of the Antique Telescope Society, no. 19: 3–12.Google Scholar
- Sorrenson, Richard J. (1989). “Making a Living Out of Science: John Dollond and the Achromatic Lens.” History of Science Society Schuman Prize Essay.Google Scholar