English: Volume II Plate XXXVIII, Figure 1 - between pp. 286 & 287 of 1898 publication called Maryland Geological Survey Volume Two. Caption:
Heliotrope This photograph shows three types of heliotrope: (a) "the simplest form", (b) Coast Survey Type, (c) Steinheil heliotrope. These three types and their means of use are described in detail in the text of the book, from the bottom of p. 290 through the end of p. 291[1]. The "simplest form" is the round mirror at far right: "Heliotropes ... are simply instruments for reflecting the sunlight to the observer at the instrument. The simplest form is a circular mirror with a screw hinged at back, giving it a universal motion." The Coast Survey type is everything but the two small mirrors at right: " ... the Coast Survey type ... consists of a telescope which is provided with a screw for fastening it into any convenient support." {"Coast Survey"} The Steinheil heliotrope is the small rectangular mirror at right: "The Steinheil heliotrope ... consists of a small sextant mirror ... This mirror has a small hole in the center ... The mirror is so mounted that it has four different motions, two about its horizontal axis and two about its vertical axis ..." {"Steinheil heliotrope"