. A practical treatise on the use of the microscope, including the different methods of preparing and examining animal, vegetable, and mineral structures. Microscopes; Microscopy. 478 MANIPULATION. this glass is placed under a magnifying power of about 100 diameters, the bands containing the fewest number of lines in them will present the appearance shown by fig. 262, in which are exhibited the lines as seen in four of the coarsest, the other six with so low a power not being visible, and even those in the fourth band requiring some care in the illumina- tion to define them satis- factorily. I
. A practical treatise on the use of the microscope, including the different methods of preparing and examining animal, vegetable, and mineral structures. Microscopes; Microscopy. 478 MANIPULATION. this glass is placed under a magnifying power of about 100 diameters, the bands containing the fewest number of lines in them will present the appearance shown by fig. 262, in which are exhibited the lines as seen in four of the coarsest, the other six with so low a power not being visible, and even those in the fourth band requiring some care in the illumina- tion to define them satis- factorily. In order to use this test, the bands are viewed by glasses of dif- ferent focal lengths, in the same manner as any 'S" â other lined objects, and the number of the bands with their lines clearly defined, wUl form a good criterion of the merits of any magnifying power from 100 to 2,000 diameters. Thus, for instance, if a quarter of an inch object-glass be employed with the best iUumination, nine of the bands may be seen, and the lines in seven of them clearly defined, but stiU no trace of the tenth band visible; if, however, a twelfth is used, the lines in the tenth may be shown; and these, although the jj^ of an inch apart, are as perfectly etched as those in the first band, which are seventy times as coarse as those in the tenth. Of all the tests yet found for object-glasses of high power, this would appear to be the most valuable, and one which comes the nearest to the utmost limit at which the position of a line xjan be accurately ascertained. M. Nobert's paper is published in Poggen- dorfs Annalen for 1846; but as it would be foreign to the object of this work to enter so scientifically into the explanation of the reasons for adopting this valuable form of test glass as M. Noberfc has done, the reader is referred to the paper itself, which will well repay an attentive perusal, as the information it contains is of the highest practical importance. Accompa- nying the tes
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Keywords: ., bookcentury1800, booksubjectmicroscopes, booksubjectmicroscopy
