Paper, 'Photometric observations of the Sun and sky' by William Brennand

Description

Brennand presents an overview of some of Henry Roscoe's research into the chemical action of sunlight. He discusses the methods employed in his own photometric observations of the Sun and sky: 'The method of measurement I adopted is the darkening produced in sensitised photographic paper; for this effect I accept Roscoe's term of "the chemical action". My method of measurement differs from that of Roscoe in one important point: I use strips cut from one uniform sheet of ordinary photographic paper; all my measurements are so far relative, and I obtain the same numerical results (ratios) with any paper. I compare ultimately the effect of the Sun and of a candle on this same paper. Roscoe, by preparing special paper with definite proportions of nitrate of silver, depends on thus reproducing paper of exactly the same sensitiveness. I make each measurement numerically (as did Roscoe) by comparing the shade produced with some standard blackness.'

Annotations in pencil and ink. Includes three photographs of Brennand's octant actinometer and Mitrailleuse actinometer.

Subject: Optics / Photometry

Received 30 October 1890. Read 11 December 1890. Communicated by C B [Charles Baron] Clarke.

A version of this paper was published in volume 49 of the Proceedings of the Royal Society as 'Photometric observations of the Sun and sky'.

Reference number

PP/17/18

Earliest possible date

1890

Physical description

Ink and graphite pencil on paper

Page extent

44 pages

Format

Manuscript
Photograph