. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. they a6t, by means i62 MICROSCOPICAL MANIPULATION. of milled-heads, like a small pair of callipers, areplaced as just mentioned. The distance on theobjedl is measured between these points, and, uponthe removal of the slide, the value of the space canbe estimated by putting the stage micrometer in itsplace. For counting striae and other marks in agiven space, and for many purposes, this simplecontrivance is very effedtive, as, also, where thegl
. On microscopical manipulation : being the subject matter of a course of lectures delivered before the Quekett Microscopical Club, January-April, 1869. they a6t, by means i62 MICROSCOPICAL MANIPULATION. of milled-heads, like a small pair of callipers, areplaced as just mentioned. The distance on theobjedl is measured between these points, and, uponthe removal of the slide, the value of the space canbe estimated by putting the stage micrometer in itsplace. For counting striae and other marks in agiven space, and for many purposes, this simplecontrivance is very effedtive, as, also, where theglass of the stage micrometer might interfere withthe definition of a very delicate objedt. In making the scales on microscopical drawings,it is often necessary to divide a given space into acertain number of equal parts. When the numberis a multiple of two, it is readily performed by acontinued process of bisedtion; but, as ten is anumber frequently required, this process will notserve beyond the first bise<5tion, which leaves five—a rather troublesome number to guess at with thecompasses. Suppose the line a, b (Fig. 44) is to beFig. 44, 42 c. divided into five parts. From a, rule the line a cat any convenient angle, of any suitable length ;from B, rule b d, parallel to a c ; from a, set off, withthe compasses, five equal spaces (i, 2, &c.) towardsc; and, from b, set off the same towards d ; join DRAWING MATERIALS. 163 I, I; 2, 2; 3, 3; &c.; and the lines i, i, &c., willdivide a b into five equal parts. Any number ofdivisions may be made b} setting off the numberrequired on a c and b d. If scales are employed for setting off distances,those known as feather-edged scales are to bepreferred, as they do not require the use of com-passes, the divisions being marked direcftly on thepaper from the thin edges. For general purposes,that known as a builders scale is convenient, as itcontains a large number of different scales, all ofwhich are ingeniously contrived to read at the edg
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectmicroscopy, bookyear1
