His heliometer (described in a paper communi cated to the Royal Society in 1743, and FIG.
By Merz in 1839 on the model of Bessel's heliometer, submits the following suggestions for its improvement: 1 (I) to give automatically to the two segments simultaneous equal and opposite movement; 2 and (2) to make the tube of metal instead of wood; to attach the heliometer head firmly to this tube; to place the eye-piece permanently in the axis of the telescope; and to fix a strong cradle on the end of the declination axis, in which the tube, with the attached head and eye-piece, could rotate on its axis.
This lens is divided and mounted like a heliometer objectglass; the separation of the lenses produces the required double image, and is measured by a screw.
A series of observations can be easily and more accurately accomplished with the Cape heliometer in half an hour; with the Oxford heliometer it would occupy 2 hours, and with the 4-in.
Again, in an ocular heliometer by Steinheil double image is similarly produced by a divided prism of total reflection placed in parallel rays.
I.; Hansen, Ausfahrliche Methode mit dem Fraunhoferschen Heliometer anzustellen (Gotha, 1827); Chauvenet, Spherical and Practical Astronomy, vol.
The first heliometer of the modern type.
When the heliometer-part of Lord Lindsay's heliometer was acquired by Gill in 1879, he changed the manner of imparting the motion in question.
To remedy drawback (2) Repsolds provided for the Yale heliometer an additional handle for motion in position angle, intermediate in velocity between the original quick and slow motions.
Still more recently the Repsolds have completed a new heliometer for Yale College, New Haven, United States.