They were made of glass lenses, and refractors were how telescopes were made until they became so big that it was impossible to support such a large weight of glass as the primary lens aperture of the telescope, at which point the design moved towards the reflecting telescope because it was easier to engineer.
Elles étaient fabriquées avec des lentilles de verre jusqu’à ce qu’elles deviennent si grandes qu’il soit impossible au tube de supporter à son extrémité un poids trop lourd.