Definition of "sciatherical"

Here I ought to mention the Sciatherical Instruments, for Want of which there was a Time when the Grecians themselves were forced to measure the Shadow, in order to know the Hour of the Day.

1745, Francis Holliday, Syntagma Mathesios: Containing the Resolution of Equations, London: J. Fuller, page 24

[The cromlech] could not be primarily intended either as a Religious Structure, or a Sephulchral Monument, but was partly design'd for Sciatherical Purposes, and in general as the Apparatus of an ASTRONOMICAL OBSERVATORY.

1778, William Chapple, Sciatherica Antiqua Restaurata

Here I may also mention the sciatherical instruments, for want of which there was a time when the Greeks themselves were obliged to measure the shadow, in order to know the hour[.]

1801, David Morrice, Mentor, Or, The Moral Conductor of Youth from the Academy to Manhood, London: Messrs. Rivingtons, Richardson, and Hatchard, page 262

The Lumincus [sic] Lamp of Progression, whose sciatherical shadows falling upon earthly matter, not promoting sciolism, or Siccity, may it illumine humanity as it tardigradely floats from matter's aquius wastes, to minds majestic and apyrous climes.

1875, Marietta Holley, My Opinions and Betsey Bobbet's, Hartford, Conn.: American Publishing Company, page 172

[W]ould the new Narcissus—without any dioptric or sciatherical computing—grasp the alternating skirmish of light and shadow.

2014, Umberto Eco, Island of the Day Before, London: Vintage Books, page 363