Baseline building, Lough Foyle
Date
1830
Creator
Unknown, Artist
Object type
Archive reference number
Material
Dimensions
height (drawing): 130mm
width (drawing): 297mm
width (drawing): 297mm
Subject
Content object
Description
Sectional elevation of the proposed building intended to protect the baseline used in triangulation measurements for the Ordnance Survey of Ireland, supervised by Thomas Colby. The section shows the removable capstone, intended to allow access to the baseline.
An accompanying letter by Thomas Colby, Ordnance Map Office, Tower of London, to Davies Gilbert notes that: ‘In the enclosed sketch and section, the buildings are of such a diameter as to clear the foundations of the blocks and of such an altitude that the view from our instrument placed upon them would not be obstructed by ordinary fences. The centre of the roof is formed of a stone having a hole in it to admit a smaller stone placed accurately over the point; which latter may be taken out without disturbing the building, and a boy may go down to clean the point …’
Inscribed below the main figure: ‘Length of Foundation stones 8 ft.’ Inscribed below right: ‘Scale 4ft to an Inch’.
Thomas Frederick Colby (1784-1852) surveyor and army officer, was elected a Fellow of the Royal Society in 1820.
An accompanying letter by Thomas Colby, Ordnance Map Office, Tower of London, to Davies Gilbert notes that: ‘In the enclosed sketch and section, the buildings are of such a diameter as to clear the foundations of the blocks and of such an altitude that the view from our instrument placed upon them would not be obstructed by ordinary fences. The centre of the roof is formed of a stone having a hole in it to admit a smaller stone placed accurately over the point; which latter may be taken out without disturbing the building, and a boy may go down to clean the point …’
Inscribed below the main figure: ‘Length of Foundation stones 8 ft.’ Inscribed below right: ‘Scale 4ft to an Inch’.
Thomas Frederick Colby (1784-1852) surveyor and army officer, was elected a Fellow of the Royal Society in 1820.
Associated place