Kirkhill Astronomical Pillar
The model, centred on a Sun of stone six feet in diameter with planets at distances and sizes to scale, has long since disappeared; only the pillar remains.
As a young child Erskine was taught at home by his parents, both of whom had studied (and met each other) in the classes of the famous mathematician Colin Maclaurin at Edinburgh University.
By the beginning of the eighteenth century the Copernican model of a heliocentric Solar System was well established and astronomers such as Tycho Brahe and Johannes Kepler were able to describe the motions of the planets with ever greater precision.
[d] The breakthrough came in 1639 when Jeremiah Horrocks made the first scientific observation of a transit of Venus and used his results to estimate an approximation for the AU.
[5][6] A second method, proposed in 1663 by the Scottish mathematician James Gregory,[7] was promoted by Edmond Halley in a paper published in 1691 (revised 1716).
The event of 1761 produced sparse results because travel overseas was greatly hindered by the Seven Years' War but in 1769 many observers were again despatched all over the world, amongst them being Captain James Cook on behalf of the Royal Society of London.
In Scotland, both transits were observed by Erskine's friend and neighbour, Reverend Alexander Bryce,[f][10][11] minister of the church at Kirknewton, only 3 miles from Kirkhill.
In his 'Account of the Parish of Uphall', Erskine writes:[12] "In the year 1776, I caused a representation to be made of the solar system, on a scale of 12,283 miles and 28/100 to an inch; the table of which epitome[h] is engraved on a belfray which stands in the middle of my garden, and of which I shall insert a transcript below.
[13] The table giving the dimensions of his representation is carved into the east face of the stone pillar, or belfry; it is barely legible now, but the details are preserved in the Uphall account.
[14] Planet diameters and distances on the pillar are reproduced here, along with the values obtained by scaling inches up to miles, by a factor of 12,283.28.
Nowadays the term axial tilt is used by astronomers: it defines the angle between the rotation axis and the normal to the plane of the orbit and it is equal to 90 degrees minus Erskine's inclination.
The order of zodiac constellations is Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, and Pisces.
Ille ego qui quondam patriae perculsus amore, Civibus oppressis, libertati succurrere aussim, Nunc Arva paterna colo, fugioque liruina regum.
Primrose gives the translation: To James Buchanan, Professor of Mathematics at Glasgow,[k] the most incorruptible guardian of my youth, have I dedicated, inscribed with my own hands, these Academic Amenities, and I wish them to be sacred.
On the 15th year of his death and from the birth of Christ 1771, I who formerly animated by love of country, dared to succour liberty and oppressed citizens, now cultivate my paternal fields and shun the threshold of Kings.
A quotation from Vergil's Georgics: DIGNA MANET DIVINA GLORIA RURIS which may be translated as "Pay homage to the heavenly sent land" or "The worthy glory of the Divine Country is abiding"[13] Underneath the inscription is a large bow and arrow the significance of which is unknown, the sign for Scorpius, and an unidentified sign.
The mention of Kirknewton Manse links this inscription to its resident, Alexander Bryce, who provided the details of the epitome table.
Similarly time displacements of the observatories at Edinburgh and Glasgow should be read as 1′8′′ (not 1°8") and 3′11′′50′′′ respectively, corresponding to 17 and 48 arc minutes of longitude, or 11 and 31 miles.
The height differences between the pillar and locations in Edinburgh are an interesting by-product of Bryce's survey of a canal from the city, past Kirkhill and on to Falkirk.
[10] Since there were to be no locks between the city and Broxburn the height of the pillar was easily related to that of the canal terminus and hence other known Edinburgh locations.
[19] The Sun is represented by a light box on the top of Broxburn academy, within a few hundred metres of the Erskine's own house.
