A refracting spyglass of the 1660s threw coloured fringes — the same colour problem as the prism demo. Newton ground a metal mirror instead, put a small flat at 45° to send the focus out the side, and avoided glass dispersion altogether. The tube he showed in 1668 was a few inches long.
Speculum metal tarnished; later mirrors were silvered glass. The layout stayed. This bench is the classic: concave primary, diagonal, eyepiece, white sky in.