The solar polariscope, like the solar microscope, is a projection instrument.
The exemplars of the two instruments in this collection are both used in combination with the same heliostat; but while the microscope must be illuminated with a beam of natural light and it makes no difference if one uses the beam reflected from the back face of the mirror, on the contrary one gains in intensity, the polariscope must be illuminated by a linearly polarized beam of light. Therefore, with the polariscope, not only must the incidence on the plate of glass of the heliostat be the one known as Brewster's heliostat, but, if the beam reflected by the back face, which is partially polarized and vibrates perpendicularly in the direction of vibration of the beam reflected by the front face is to be avoided, then the back face must be blackened as in the one in this collection.
The device, all made of brass, consists of a tube blackened on the inside and divided into three parts.
The first part, which has a diameter of 9 cm, acts as the support and is screwed onto the heliostat in place of the tube.
The second fits inside the first and can slide by up to 12 cm; the third tube slides inside the final part of the second tube, which has a diameter of 6 cm, by about 13.5 cm. ...continues