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Description: | National Physical Laboratory, KEW OBSERVATORY, RICHMOND, SURREY. CERTIFICATE OF EXAMINATION. CLASS A. THE SEXTAT No. 6148 of 7 inches radius named H. Huhes & Son Ltd London divided on silver with vernier showing 10" has been examined at this institution. The shades and mirrors are found good. The telescopes are also satisfactory and the powers are, for the inverting 13 and 6 linear and the erect 3 &3 linear. The following are the corrections to the readings of the arc (in addition to the index correction):- {thererfollows a table of angles 15, 30, 45, 60, 75, 90, 105, 120 degrees The corrections for these angles are all zero} + means- Addative - means- Subtractive. July 1908 R.J. Glazebrook DIRECTOR (printed and in part written in ink on the card pinned to the inside of the lid of the box). 6148 H. HUGHES & SON LONDON (engraved on the arc). )-140 ( engraved on the silver scaleof the arc in 10's divided by 60) 0-10 (engraved on the silver vernier scale in units of 2 divided by 12). MANU Henry Hughes and Son Limited circa 1800 The sign of the orrery,136 Fleet Street, London, England DES after WRIGHT, George or Thomas before 1780 England. DES after BIRD,John. 1757 London, England. This instrument, more accurately called a pentant, is one of a group of navigational and surveying instruments, including the octant and sextant, which in modern parlance are now generically all called sextants. The sextant was designed circa 1760 after the introduction of the lunar distance method in 1757, which required greater accuracy than the quadrant could achieve.
The quintant is a 144 degree arc version of the sextant and was used as navigational and hydrographic surveying instrument but was more commonly used as a land surveying instrument because of its ability to measure larger azimuth angles with a mercury mirror artificial horizon. See GLAHM 113912.
This 10 inch 254 mm arc instrument has a combination of three shades; one grey, one gray-green, and one blue-gray. It has a 175 mm radius scale and can be read to 1 sec. The index arm which is reinforced has a venier microscope and a tangent screw clamp. The oxidised brass frame has lattice struts. The construction reduces the weight and wind resistance of the instrument for easier handling without compromising the stiffness, which would reduce its accuracy.
There were two interchangeable backsights; a terestial, and an astronomical. N.B. the forsight mirror is adjustable. As in Hadley's quadrant the mirror halves the scale. | License: | http://www.hmag.gla.ac.uk/spirit/rights/ | Publisher: | Hunterian Museum and Art Gallery, University of Glasgow | Rights holder: | Hunterian Museum and Art Gallery, University of Glasgow | Subjects: | SCIENTIFIC COLLECTION : | Source: | Hunterian Museum | Creator: | Hunterian Museum and Art Gallery, University of Glasgow | Identifier: | http://www.huntsearch.gla.ac.uk/cgi-bin/... | Language: | en-GB | Go to resource |
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