‎"BARLOW, PETER. - THE ""BARLOW LENS""‎
‎An Account of the Construction of a Fluid Lens Refracting Telescope of eight inches aperture, and eight feet and three quarters in lenght, made for the Royal Society by george Dolland. Read November 22, 1832.‎

‎(London, Richard Taylor, 1833). ‎

Reference : 44051

‎First printing of the paper in which he describes the 8 inch-telescope with the fluid lens - the so-called second Barlow-lens - required by the Royal Society for testing.""Barlow’s next major contribution makes his name still well known by amateur astronomers today. He invented the Barlow lens, a telescope lens consisting of a colourless liquid between two pieces of glass. The ""Barlow lens"", a modification of this telescope lens, is a negative achromatic combination of flint glass and crown glass. It is a negative lens used to extend the effective focal length of a telescope objective.""""His optical experiments began about 1827. There were several experiments to correct a single lens for chromatic aberration with concave lenses. These correctors were first placed near the first lens, but some opticians moved the concave lens further down the tube. This arrangement was described 1828 by Rogers in a paper to the Astronomical Society. By this a 3 inch concave flint lens was sufficient to correct a 9 inch crown glass. Smaller lenses near the focus would do the colour correction, but have to have steeper curves which would introduce spherical aberration."" ‎