In these observations, it is understood that the observer obtains distinct vision of the pictures in the stereoscope, either by the adjustment of the moveable eye-tubes, if they are moveable, as they ought to be, or by the aid of convex or concave glasses for both eyes, either in the form of spectacles, or separate lenses placed immediately above, or immediately below the semi-lenses in the eye-tubes. If the eyes have different focal lengths, which is not unfrequently the case, lenses differing in convexity or concavity should be employed to equalize them.
EDINBURGH: T. CONSTABLE,
PRINTER TO HER MAJESTY.
Footnotes:
[1] Edit. of Pena, pp. 17, 18, Paris, 1577; or Opera, by Gregory, pp. 619, 620. Oxon. 1703.
[2] De Usu Partium Corporis Humani, edit. Lugduni, 1550, p. 593.
[3] Joan. Baptistæ Portæ Neap., De Refractione Optices parte, lib. v. p. 132, and lib. vi. pp. 143-5. Neap. 1593.
[4] Trattata della Pictura, Scultura, ed Architettura. Milan, 1584.
[5] Dr. Smith’s Compleat System of Opticks, vol. ii., Remarks, pp. 41 and 244.
[6] Opticorum Libri Sex Philosophis juxta ac Mathematicis utiles. Folio. Antverpiæ, 1613.
[7] In [Fig. 1], ahf is the optical pyramid seen by the eye a, and bge the optical pyramid seen by the eye b.