The telescope in the window was down as a Dobsonian reflector and I wondered what that meant. Turns out that it is not to do with the optics inside but to do with the mounting. This article explains the history. The significance is that it made it easier to mount bigger mirror reflector telescopes so reducing the cost for amateur astronomers. The advantage of reflectors is that the heavy glasswork is at the bottom of the light gathering tube so they are easier to support. This means reflectors are easier to build with larger diameters so have more light gathering power.
