Cornelius Varley constructed microscopes from the 1820's through the third quarter of the nineteenth century. During this time, one of the light sources felt to be optimal for substage illumination was a clear white cloud on a sunny day. Unfortunately this kind of cloud does not appear every day. Varley devised a device which would convert direct sunlight into a white light similar to a white cloud. This device uses a reflector of plaster of Paris instead of a mirror, thus converting dangerous and yellow sunlight to white light. To intensify the light, a bullseye condenser lens was used. These condenser lenses could be freestanding, but could also be adapted directly to the illuminator as is the case for the accessory depicted on this page, or be supplied as an accessory piece that fit over the mirror. Jabez Hogg, writing in his 1854 edition of 'The Microscope, Its History, Construction and Application', credits Varley for this invention on page 53. Several other authors also give credit for this to Varley.