Nevertheless, disks of optical glass, both crown and flint, have been produced up to 39 in.
The planets were shown to have visible disks, and to be attended by satellites whose distance and position angle relative to the planet it was desirable to measure.
Ical tele- Two disks of thin metal, or two stretched membranes, each furnished with a mouthpiece, are connected together by a thin string or wire attached at each end to the centres of the membranes.
The space enclosed between the front and rear faces of the box is filled about three-quarters full of finely granulated hard carbon, which therefore lies in contact with the front and rear carbon disks of the apparatus, and also fills up the space lying between the lower edge of these disks and the curved surface of the case.
The current from the battery passes from one of the carbon disks to the other through the particles of granulated carbon which fill the space between them.