On an Improved Finder. By W. Wehh. 751 



To number the squares from 1 to 22,500 would require more 

 than 100,000 figures, which renders numbering impossible ; the 

 squares are therefore plotted in blocks of 100, the boundary lines 

 of each block of 100 squares being cut deeper, broader, and blacker 

 than the inner ones (excepting four lines which I will describe 

 presently), each block consisting of ten rows of squares, and each 

 row containing ten squares. Each block of 100 squares is inter- 

 sected vertically and horizontally at its fifth divisions by lines less 

 black than those forming the boundaries of the blocks of 100 squares, 

 but still appreciably blacker and broader tban the inner lines, thus 

 subdividing the blocks into four minor ones, each having five rows 

 with five squares in each row, the clear distinction between the 

 three kinds of lines commanding ready and unmistakable recog- 

 nition. 



To reduce the finder to its greatest simplicity in working over 

 the three-quarters of an inch, 1 have introduced the four special 

 lines above referred to, they being broader than all the others, and 

 two of them embracing two sides of every eighth block of 100 

 squares from the top to the bottom of the finder, and the other 

 two lines embracing two sides of every eighth block of 100 squares 

 from the left to the right, the four lines thus forming the 

 boundaries of the central hlock of 100 squares, and the inter- 

 section of the two lines which divide that block into smaller blocks 

 of 25 squares is the central point of the finder, from which the eye 

 has only to traverse tbrough 75 squares vertically or horizontally 

 to locate any square wanted 



Fig. 71 represents a little more than the top left-hand quarter 

 of the finder (the finest divisions not being however shown). It 

 exhibits the central intersecting point of the finder, giving out- 

 side the broad lines 7 blocks of 100 squares each vcrticallj and 7 

 horizontally. 



Fig. 72 is an enlarged view of one of the blocks of 100 squares, 

 with the addition of the Hnest lines forming those squares. 



It will be readily seen, by looking at these two figures, that from 

 the centre of the finder the whole of the 22,500 squares can be 

 easily found by traversing at the very most 75 small squares from 

 the centre, with the same ease and certainty as the eye traverses the 

 long and short lines of the eye-piece micrometer, the breadth of tho 

 line in the finder being as easily distinguishable as tho length in tho 

 eye-piece micrometer. 'J'he square having one dot in Fig. 72, 

 (assuming that figure to show the central block of the finder), would 

 be one square on the left of and ahove tho centre, to bo marked 

 " 1 1. a." ; the square with two dots would lie the second square 

 horizontally and vertically to the left of and ahove the centre, to Ix) 

 marked " 2 h. 2 v. 1. a." ; tho square with three dots would bo 

 tho fourth horizontally and tho third vertically, to be marked 



