I read in several sites that Gauss made several contributions to technology, and that his main contributions were: the heliotrope, improvements of several optical devices (telescopes, introduction of Gauss-lenses,...), the photometer, magnetometer (and maybe several other electromagnetic instruments), and the electromagnetic telegraph. Actually, pages 186-189 of Clemens Schaefer's treatise on Gauss's contributions to physics deal with Gauss's small contribution to photometry. According to them, Gauss tried to establish a reliable method for photomety of stars - i.e for a quantitive measurement of the brightness of star. At his time, such a method didn't exist yet.

Schaefer gives additional details about Gauss's own description of his design of photometer, according to which it was a comparative photometer that was able to "tune" the intesity of light from two stars, until the stars appeared "equally bright" to the eye (and that was something that had to be determined visually by the eye). Then the stars's relative brightness could be established by knowledge of the brightness magnification factor applied by the instrument. Gauss also described very clearly the difficulties in the problem of heterochromatic photometry (the problem of visually deciding whetever two light sources of different colours are equally bright).

Also, in Gauss: Titan of Science, Dunnington mentions that Gerling constructed a photometer according to principles outlined by Gauss. But despite of this, i coundn't find any information about the photometer which Gauss invented in the english literature. I'll specify what i want to know:

  • What was the internal structure of Gauss's photometer? what were his principles of operation? as far as i know, a comparative photometer must have two essential abilities: bringing the image of the measured star to the proximity of a standard source (even if the star might be angulary distant from the known source), and magnification of the brightness of one star. Gauss's comparative photometer must be judged by these criterions.
  • Did Gauss's photometer have any importance for the later developement of comparative photometers?
  • $\begingroup$ I think not; the Weber who invented the first good photometer was much later than the Weber that worked with Gauss. I don't find any references to a photometer (or related devices) when looking at detailed accounts of Gauss, but I do see them sometimes with brief summaries of his work - but not in Encyclopedia Britannica. $\endgroup$ May 16, 2016 at 20:54
  • $\begingroup$ Shouldn’t your update rather be posted as an answer? $\endgroup$ Oct 11, 2018 at 13:11
  • $\begingroup$ @Francois Ziegler - it is an answer to the previous version of the title question (Did Gauss invent a photometer?) but not to this one (What were the scientific principles of Gauss's photometer?) - my update didn't describe the internal structure of Gauss's "photometer" (Schaefer does indeed give some technical details on this photometer, but i didn't undrestand them, so i need further explanation). $\endgroup$
    – user2554
    Oct 11, 2018 at 15:11
  • $\begingroup$ Then what you want to know should really be spelled out in the body (of this or another question). Right now it reads “is there any reference?” followed by “Update: Yes, Schaefer” and no further query. It just seems answered. $\endgroup$ Oct 11, 2018 at 15:44
  • 1
    $\begingroup$ I've modified my question. $\endgroup$
    – user2554
    Oct 12, 2018 at 10:51


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