Transactions . Fig. 1. number of trial-glasses behind the eye, permits them to berapidly changed, while the instrument is nearly as small as 110 Lorings. It consists of the ordinary mirror, beliind which two discs can be rotated like the diaphragm in some—for instance, Kellners—microscopes. In each disc are thirteen little aper- A B. Fig. , twelve of which are filled with glasses, one being empty,(see Fig. 2 A.) One disc contains convex, the other concaveglasses, in the following progression: 3, 4, 6, 8, 10, 12, 14, 17,20, 24, 33, 48. The intervals of refractive power betweenthese nnmbe
Transactions . Fig. 1. number of trial-glasses behind the eye, permits them to berapidly changed, while the instrument is nearly as small as 110 Lorings. It consists of the ordinary mirror, beliind which two discs can be rotated like the diaphragm in some—for instance, Kellners—microscopes. In each disc are thirteen little aper- A B. Fig. , twelve of which are filled with glasses, one being empty,(see Fig. 2 A.) One disc contains convex, the other concaveglasses, in the following progression: 3, 4, 6, 8, 10, 12, 14, 17,20, 24, 33, 48. The intervals of refractive power betweenthese nnmbers are as follows: between 3 and 4 = y^; 4 and 6= ^\; 6 and 8 = ^V ; 8 and 10 = ^\ ; 10 and 12 = ^o ; 12 and14 = j\; 14 and 17 = ^V ; 17 and 20 = ^1-3 ; 2*) and 24 = yi^ ;24 and 33 = j\; 33 and 48 = j^-g. The weaker nnmbers whichoccnr more frequently in practice, show very small intervals ofrefraction. These two series of glasses are sufficient for themajority of cases coming before the practitioner. To avoid,however, any loss of time, both discs are placed behind themirror, and the change from one glass to any other is effectedby a very easy rotation of the disc. The discs are held Note.—In the new instruments -t- 2 and — 2 are added. Ill place and protected from beinsi: soiled by a thin metal plate,(Fig. 2 B.,) which co
Size: 1525px × 1638px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1860, booksubjectophthalmology, bookye
