History of Telescope

choi

This posting is about Euler, Newton and Dollond.

(1) Telescope
https://en.wikipedia.org/wiki/Telescope
(section 1 History)
(a) Competition between reflecting telescope and refracting telescope, each with pros and cons.

Below I am quoting the above Wiki page.
(i) "The idea that the objective, or light-gathering element, could be a mirror [alluding to a reflecting telescope] instead of a lens was being investigated soon after the invention of the refracting telescope."
(ii) "The invention of the achromatic lens in 1733 [the year an Englishman Chester Moore Hall alleged invented achromaic lens, but there was nothing to support the claim except Hall's words] partially corrected color aberrations present in the simple lens and enabled the construction of shorter, more functional refracting telescopes."

This sentence will be explained.
(b) Partial Reflection/Refraction. In Properties of Waves.
https://sites.google.com/site/pr ... flection-refraction
(c) "Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by the use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th century"
(i) Why is it called speculum metal, I fail to find out. But "speculum metal is a mixture of around two-thirds copper and one-third tin making a white brittle alloy that can be polished to make a highly reflective surface."
https://en.wikipedia.org/wiki/Speculum_metal
(ii) speculum (n, etymology): "an instrument inserted into a body passage [such as vagina] especially to facilitate visual inspection or medication"
https://www.merriam-webster.com/dictionary/speculum

choi

(2) John Dollond. In William Howse Groser, Men Worth Imitating; Or, brief sketches of noble lives. (1871) at pages 32-36.
https://todayinsci.com/D/Dollond_John/DollondJohn-Bio(1871).htm
(a) Newton as "the discoverer of the composition of light"

visible spectrum
https://en.wikipedia.org/wiki/Visible_spectrum

Quote:

"Isaac Newton discovered that prisms could disassemble and reassemble white light, and described the phenomenon in his book Opticks [in English 1704, in Latin 1706].

"Newton divided the spectrum into seven named colors: red, orange, yellow, green, blue, indigo, and violet. He chose seven colors out of a belief, derived from the ancient Greek sophists * * * the evidence indicates that what Newton meant by 'indigo' and 'blue' does not correspond to the modern meanings of those color words. Comparing Newton's observation of prismatic colors to a color image of the visible light spectrum shows that 'indigo' corresponds to what is today called blue, whereas 'blue' corresponds to cyan.

(b)
(i) Spitalfields
https://en.wikipedia.org/wiki/Spitalfields
(section 1 Toponymy)
(ii) spital (n): "archaic  LAZARETTO, HOSPITAL"
https://www.merriam-webster.com/dictionary/spital
(c) "Thus he [John Dollond] contrived to become a proficient in various branches of natural philosophy"

In both Oxforddictionaries.com and www.merriam-webster.com, the word "proficient" is an adjective (only), not a noun.
(d) "Meanwhile the telescope remained as Newton had left it. The great mathematician, Euler, attempted to meet the difficulties [with a refracting telescope] which had foiled the English philosopher [Newton]; but without success.
(e) "This bold and unprecedented idea was tested by a long series of experiments resulting in the clearest proof that the inference was well founded, and that the supposed insurmountable obstacle [chromatic aberration, see (3) below] to the improvement of the telescope had no existence."

(f) "The truth of Dollond's conclusion was at length duly recognised abroad as well as at home, and he was honoured by the Royal Society, not only with a fellowship in that distinguished body, but also with the Copley Medal awarded to eminent discoverers."
(i)  at length
"1:  very fully <We discussed the problem at length>
2:  at the end :  FINALLY <They decided at length to order pizza>"
https://www.merriam-webster.com/dictionary/length
(ii) Copley Medal
https://en.wikipedia.org/wiki/Copley_Medal
(Given every year; probably the oldest surviving scientific award in the world, having first been given in 1731 to Stephen Gray; section 1 History)

(g) "Well says the Eastern proverb, 'A stone that is fit for the wall is not left in the way.' "
(i) Annette Kinnear, Your Career, Your Life; Fast-track to success. Penguin, 2012, at page (not shown).
https://books.google.com/books?i ... 0Trench&f=false
(paragraph 2 under the section heading "Week 6": "Richard C Trench said, 'A stone that is fit for the wall is not left in the way.' That's how it is in companies. Many, if not all, bosses will go to great lengths to keep an excellent employee happy, and will work around his or her known needs")
(ii) Richard Chenevix Trench
https://en.wikipedia.org/wiki/Richard_Chenevix_Trench
(1807 – 1886)

choi

(3)
(a) chromatic aberration
https://en.wikipedia.org/wiki/Chromatic_aberration
(resulting from dispersion; "leading him [Newton] to build the first reflecting telescope, his Newtonian telescope, in 1668")

Quote: AXIAL chromatic aberration "can be further minimized by using an achromatic lens or achromat, in which materials with differing dispersion are assembled together to form a compound lens. The most common type is an achromatic doublet, with elements made of crown and flint glass."
(I add axial here, not Wiki, in view of (3)(c) below.)
(b) The above Wiki page demonstrates a pair of photos for the effect. Here is one from Apple.

Working with the Chromatic Aberration Controls. In Aperture 3 User Manual.
https://documentation.apple.com/ ... ion=11%26tasks=true
(i) The Apple example is axial, not lateral, chromatic aberration. See (3)(c) and (d).
(ii) Aperture (software)
https://en.wikipedia.org/wiki/Aperture_(software)
(table: Initial release 2005, Last release 3.6 on Oct 16, 2014)
(c) Interchangeable Lenses – Chromatic Aberration Compensation; Essential technologies of lens design that enhance resolving power. Nikon, August 2014.
www.nikon.com/about/technology/life/imaging/aberration/index.htm

Quote:

"Axial chromatic aberration is compensated using convex and concave lenses that counterbalance each other.

"In lateral chromatic aberration, by using optical symmetry around the aperture, lateral chromatic aberration that occurs in front of the aperture is canceled by that occurring behind the aperture in the reverse direction." (In the illustration, take notice of "Photographic subject [or, light] outside the optical axis."

(d) Compare axial and lateral chromatic aberration side by side.

Astronomical Optics Part 4: Optical Aberrations
www.handprint.com/ASTRO/ae4.html

A pair of circles full of polka dots under the sectional heading "Chromatic Aberrations": every dots in axial aberration is uniformly affected, whereas the dots in the periphery (but not in the center) are affected -- the more peripheral, the worse.

choi

(4)
(a)
(i) crown glass. Encyclopaedia Britannica, undated
https://www.britannica.com/technology/crown-glass
(crown glass was slightly convex; The crown process, which may have been Syrian in origin, was in use in Europe since at least the 14th century)
(ii) What is the derivation of the name 'crown glass' (the type used in optics, such as Fresnel lenses)?  Aleš Lombergar (The beauty of acid etched glass)
http://www.aleslombergar.com/for ... -as-fresnel-lenses/
(answer: "From [older] wikipedia: Crown glass was an early type of window glass. In this process, glass was blown into a 'crown' or hollow globe. This was then flattened by reheating and spinning out the bowl-shaped piece of glass (bullion) into a flat disk * * * ")
(b) flint glass
https://en.wikipedia.org/wiki/Flint_glass
(has relatively high refractive index)

Quote: "With respect to glass, the term flint derives from the flint nodules found in the chalk deposits of southeast England that were used as a source of high purity silica by George Ravenscroft, c 1662, to produce a potash lead glass that was the precursor to English lead crystal.

(i) flint
https://en.wikipedia.org/wiki/Flint
(It [Flint] occurs chiefly as nodules and masses in sedimentary rocks, such as chalks and limestones; view photo 1 only)
(ii) Richard Milton, What Is Flint?  Museum of The Stone Age, undated
http://www.stoneagetools.co.uk/what-is-flint.htm
("Flint (chert) is a form of quartz, or silicon dioxide, also called silica")

(5) Richard Sorrenson, Dollond & Son's Pursuit of Achromaticity, 1758-1789. History of Science, 39: 31-55 (2001).
http://adsabs.harvard.edu/full/2001HisSc..39...31S