WHY THE PROJECTION PLANETARIUM WAS NOT CONCEIVED OR INVENTED DURING THE LATE NINETEENTH CENTURY

Abstract

This brief paper serves as a follow-up to that of the preceding authors (Smith and Snedegar 2021) and proposes to answer the question as to why the projection planetarium was <italic>not</italic> conceived (or invented) during the late nineteenth century. Had Franklin Henry Bailey's 'Astral Lantern' been employed as a simple projection device, it would have shown <italic>reversed</italic> patterns of constellations on the walls (a remediable condition), each of whose star images would have been a flickering, upside-down image of the central <italic>candle flame</italic>. Without (1) replacing this simple light source with something much more compact, such as an electrical light bulb filament, and (2) employing auxiliary optics to further brighten and condense the light, after it passed through the perforated 'star plate(s)', no realistic images could be produced of 'projected' stars. Until one (or both) of these underlying technologies became significantly developed, the notion of a viable projection planetarium remained beyond the grasp of contemporary instructors and inventors.