Abstract: An optical device is manufactured by providing a disc-shaped body of a light-conducting material on a plane surface of a disc-shaped carrier body, grinding the light-conducting material mechanically to a thickness which exceeds the desired ultimate layer thickness by at least 50 .mu.m, subjecting the light-conducting material to alternate tribochemical and mechanical polishing treatments until a thickness is obtained which exceeds the desired ultimate layer thickness by approximately 10 .mu.m, and subsequently polishing the light-conductor body tribochemically until the desired layer thickness is obtained.

Abstract: Providing a transparent layer of an oxide of an element from group IVa of the Periodic Table, notably TiO.sub.2, by providing a substrate with a solution of a compound of the element which upon heating is converted into the relevant oxide, drying the film and heating the dried film so as to form the transparent layer of the oxide. The oxide thus obtained is a form having a comparatively low refractive index. By heating the product, after providing the film, rapidly to a temperature of above 700.degree. C., preferably above 1,000.degree. C., keeping it at this temperature for some time and then rapidly cooling it again, a modification having a higher refractive index (for example, for TiO.sub.2 rutile) is obtained.

Abstract: A work medium for use in an absorption heat pump consists of a solution of a chlorofluoroalkane in a substituted amino phosphorus oxide. With such a work medium it is possible for an absorption heat pump to absorb heat at -20.degree. C. and to give up heat at 70.degree. C.

Abstract: A heat pipe contains a getter for gaseous impurities arranged in the vapor space and distributed between the vaporization wall and the condensation wall.