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Dinesh

Dinesh club

Posted: 08 Jan 2022

Taken: 08 Jan 2022

1 favorite     1 comment    55 visits

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Image and Excerpt •
The Invention of Science •
Author •
David Wootton •

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this photo by Dinesh

Cross-staff being used for surveying and astrology -- from the title page of Petrus Apianus, ‘Introductio geographica, 1533

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 Dinesh
Dinesh club
In 1471 Regiomontanus worked out a procedure for measuring the parallax of heavenly bodies and so their distance from the Earth. His procedure presumed use of a cross-shaft in a very simple instrument, a calibrated shaft along with a bar slides. You sight along the shaft and move the bar back and forth until you have lined up its ends with two points, and the angle can then be read off from the scale of the shaft. You can use a cross-shaft, for example, to measure the angle between the horizon and the sun at midday. If you know the date and have the right tables, you can then read off your latitude.. . . Page 188
3 years ago.

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