56 BAILEY, ON A UNIVERSAL 



The axes are then graduated as seen in the plate ; the small 

 divisions being each l-50th of the standard inch. 



The dotted lines G, H, I, give the outline of what will be 

 referred to as the centre-piece. 



Should it ever be desired to reproduce the Indicator by en- 

 graving or otherwise, the dimensions above given must be 

 most accurately preserved. The dimensions here given were 

 taken from the standard inch of the United States, belonging 

 to the State of New York, and preserved in the office of the 

 Superintendent of Weights and Measures in Albany. It is 

 the same as the English inch. 



The slides on which objects are mounted to be used with 

 the Indicator must have guide-lines ruled on their under side, 

 as shown in fig. 1 and 2. The horizontal line parallel to the 

 lower edge, and passing through the middle of the slide, is 

 not continued over the portion of the slide which is to be 

 occupied by the objects and their glass cover. The distance 

 of each of the vertical lines from the middle point of the 

 slide is one inch. Great accuracy in the distance between 

 these lines of the slide is not essential when they are to be 

 used with the ordinary form of the Indicator as above given, 

 but it is desirable when they are to be employed as hereafter 

 described, with a modification of the Indicator applied to a 

 moveable stage. 



The slides should all be marked with an arrow placed upon 

 their upper and right-hand corner, as shown in fig. 1 and 2, 

 to point out the edge which must always be kept in front in 

 using the slides upon the Indicator. 



The Indicator is to be used as follows : — Cut out the centre- 

 piece with a thin-bladed knife, following the outline G, H, I ; 

 then replace the piece cut out, and make a hinge for it along 

 the line G, H, by pasting underneath it a piece of thin paper 

 which will bear repeated folding, so as to connect it to the 

 rest of the card. 



The Indicator being now ready for use, it must be firmly 

 secured to the stage of the microscope, in such a position that 

 its centre as given by the intersection of the lines C, D, and 

 E, F, when viewed as an opaque object, may be exactly in the 

 centre of the field of view. If the stage is a moveable one, it 

 must be kept stationary after the Indicator is properly centred. 



The Indicator having been adjusted as above directed, the 

 centre-piece is to be turned down, and the instrument is then 

 ready for use, either to record new objects, or to find those 

 previously recorded. The slide is to be put upon the Indi- 

 cator, and guided either by the fingers or a moveable ruler, 

 so that when any object which is to be registered occupies the 



