Testing telescopic lenses
Date
17th century
Creator
Henry Oldenburg (1612 - 1677, German) , Scientific correspondent
Object type
Archive reference number
Manuscript page number
p1
Material
Dimensions
height (page): 298mm
width (page): 188mm
width (page): 188mm
Subject
Description
A scale for Roman palms (1 palm = 22.34 cm) indicating the distances at which a telescopic lens was tested. From an Italian account of Giuseppe Campani's telescopic lenses, tested in a long dark room with 'Venetian torches' by measuring the distance at which certain printed letters could be read. The test text appears to have been a printed text with fonts in gradually diminishing size.
Translated into English by Henry Oldenburg from Cl.P/2/7/001.
Translated into English by Henry Oldenburg from Cl.P/2/7/001.
Transcription
The first Telescope was of 23 Roman palmes, with some defect by reason of the veines of the objective; and with this, were read, at the distance of 2371/2 palmes, beginning from the eyes, most plainly and distinctly, in the printed paper A, the first then Lines, and of the Eleventh, the interrogative point, and some of ye letters. Of the other paper, marked B, was read, though with a little difficulty, the first word of the same line. And it is to be taken notice, yt they doe notably and with cleerness, magnify the letters of this last verse so that, as for the bignesse, they would be read very well; whence there is reason to thinke yt because the characters are confused, and, as it were, blind, our not being able to read them may not be altogether a defect in the Glasse. The 2nd, was of 16 palmes.... The 3d, was of 5 palmes,.
All these telescopes were used with a Concave, and putt in the day time to their just measure.
The tryall was made in long chambers, the windowes shutt. The object was enlightened with two Venetian torches of white ware, of the ordinary bigness of 4, held about one plame from the object, and that the light and flame might not hinder ye observation, they were covered from the eye by being put in two great lanterns, wch kept it from that part, where the beholders stood to see. There was kept no light at all in the chamber.
Transcribed by the Making Visible project
All these telescopes were used with a Concave, and putt in the day time to their just measure.
The tryall was made in long chambers, the windowes shutt. The object was enlightened with two Venetian torches of white ware, of the ordinary bigness of 4, held about one plame from the object, and that the light and flame might not hinder ye observation, they were covered from the eye by being put in two great lanterns, wch kept it from that part, where the beholders stood to see. There was kept no light at all in the chamber.
Transcribed by the Making Visible project
Object history
This account is most likely related to the ‘competition’ between telescopes made by Eustachio Divini (1635-1715) and Giuseppi Campani (1610-1685), held in Rome in 1664 at the behest of the Grand Duke Ferdinand II and Prince Leopold. Lorenzo Magalotti (1637-1712), secretary of the Accademia del Cimento in Florence, instructed Paolo Falconieri (1638-1704), a courtier at the Medici court and member of the Accademia, to compare the effectiveness of the telescopes by using two printed sheets with eleven lines of decreasingly small fonts. Sheet ‘A’ contained meaningless words made up of random letters, and the second sheet, ‘B’, contained individual letters without ascenders or descenders, and flattened out to eliminate possible shadow effects created by the grooves made by the type-face. These were to be read with a telescope from a distance, in a darkened room with two lights. Three Campani telescopes and five Divini telescopes were tested in this way in December 1664 in the Panfilio palace on the Piazza Navona. Because Matteo Campani (Giuseppe’s brother) recorded the lengths of the telescopes systematically shorter, and because Divini added a candle to the lighting, the results were not conclusive. (See Maria Luisa Righini Bonelli and Albert van Helden, Divini and Campani: A Forgotten Chapter in the History of the Accademia del Cimento (Florence: Olschki, 1981), pp. 3-43, 82 and 84).
Henry Oldenburg reported on Campani’s telescopes to Robert Boyle in 9 October 1664 (The Correspondence of Henry Oldenburg, ed. by A. Rupert Hall and Marie Boas Hall, 13 vols (Madison: University of Wisconsin Press; London: Taylor and Francis, 1965-86), II (1966), 240 (no. 331)). Oldenburg may have acquired an account of this contest either by Magalotti or Falconieri, who visited England in 1668. They were present at the meeting of 27 February 1668, when Francis Smethwick produced some telescopic glasses. For this visit, see W. E. Knowles Middleton, 'Some Italian Visitors to the Early Royal Society ', Notes and Records of the Royal Society, 33 (1979), 157-73.
Henry Oldenburg reported on Campani’s telescopes to Robert Boyle in 9 October 1664 (The Correspondence of Henry Oldenburg, ed. by A. Rupert Hall and Marie Boas Hall, 13 vols (Madison: University of Wisconsin Press; London: Taylor and Francis, 1965-86), II (1966), 240 (no. 331)). Oldenburg may have acquired an account of this contest either by Magalotti or Falconieri, who visited England in 1668. They were present at the meeting of 27 February 1668, when Francis Smethwick produced some telescopic glasses. For this visit, see W. E. Knowles Middleton, 'Some Italian Visitors to the Early Royal Society ', Notes and Records of the Royal Society, 33 (1979), 157-73.
Associated place