Caption: Portrait of Auguste Comte (1798--1857).

The positivist philosopher Auguste Comte gave the matter composition of stars as an example of something humankind can never know:

Any research that cannot be reduced to actual visual observation is excluded where the stars are concerned ... We can see the possibility of determining their forms, their distances, their magnitudes, and their movements, but it is inconceivable that we should ever be able to study, by any means whatsoever, their chemical or mineralogical structure...''
---Auguste Comte (1798--1857), 1835, quotation from Kirk Korista at Professor Korista.

Famous last words and hostage to fortune.

Only a couple or so decades after Comte's statement, the elemental composition of stars was being identified from starlight using spectroscopy (see Wikipedia: Star: Observation history; Wikipedia: Fraunhofer lines: Discovery).

It turns out that stars are mainly hydrogen and helium just as our Sun is.

Credit/Permission: Louis-Jules Etex (1810-1889), 19th century (uploaded to Wikipedia by User:P.S. Burton, 2013) / Public domain.
Image link: Wikipedia.
File: Art file: auguste_comte.html.