Light; a course of experimental optics, chiefly with the lantern . not be polished. 2 These very small mirrors are not easy to fix and to shape, even ofthe thinnest plate-glass obtainable. Minute bits of glass silvered onthe first surface, after the manner of. specula, do better. The mostconvenient material of all I have myself found to be small polisheddiscs of very thin steel, such as are sometimes used to ornament femi-nine articles. Unfortunately they are not easy to procure. Those Ihave used came off a fan. 38 LIGHT. [chap. slight angle down on the glass, and the lens b focusing thesurfac
Light; a course of experimental optics, chiefly with the lantern . not be polished. 2 These very small mirrors are not easy to fix and to shape, even ofthe thinnest plate-glass obtainable. Minute bits of glass silvered onthe first surface, after the manner of. specula, do better. The mostconvenient material of all I have myself found to be small polisheddiscs of very thin steel, such as are sometimes used to ornament femi-nine articles. Unfortunately they are not easy to procure. Those Ihave used came off a fan. 38 LIGHT. [chap. slight angle down on the glass, and the lens b focusing thesurface on the ceihng. On now ringing the glass by theedge of a knife, circular waves of light and shade will beseen : and on dipping the finger in the alum-water and—holding the stem firmly down—rubbing the edge till thewell-known sound is produced, small ripples will cover thesurface in exquisite patterns, and follow the finger round, allbeing reproduced above on the ceiling. With a large thinglass the pattern may often be varied by pressure, but glasses ZlJ^-^. Fig. 26. differ. A violin-bow, besides being in the way, producessomewhat too strong vibrations. If an Argand burner is used, we want all the light, and the reflectorand glass must be so brought up near the nozzle, that all is collectedjust into the circumference of the water. All scattered light must alsobe carefully stopped ; covering the side-openings of the ordinary slide-stage with a cloth, seeing no light escapes anywhere, and standing theglass itself on a piece of black cloth, that no light may be reflected fromthe table surface to the ceiling. In working with a low illuminationmuch depends on these precautions, and with them this beautiful ex-periment will show very fairly on a ceiling 9 or 10 feet high; a reflectorin the lantern is also of service. With the lime-light we need notbe so particular, and the parallel beam will be best. n.] THE REFLECTING MIRROR. 39 The vibrations due to sound may be shown by theref
Size: 1679px × 1488px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1880, bookidcu3192403121, bookyear1882
