OBJECT FINDERS. 189 



left side of the microscope stage. The scales may be ruled 

 in brass or bronze and inlaid, and horizontal lines might 

 be ruled on the surface of the stage as a guide for placing 

 the slide. This form of instrument possesses the advantage 

 of not requiring the common object slides to be ruled, or 

 in any way prepared. 



It is thus used : — 1st. Put the finder on the stage and 

 find the central needle hole with the microscope. 2d. Re- 

 move the centre-piece with a small pair of forceps. 

 3d. Place the slide on the wood, taking care that the stage 

 screws he not used to move the object after the finder has 

 once been centred. 



The position of any object then occupying the centre of 

 the field will be shown by the sides and ends of the slide 

 on the scales of the finder, and can be registered at sight. 

 To find the object again : — Find the centre hole, remove 

 the disk as before, then place the slide according to the 

 letter and number marked upon it, when the object sought 

 will occupy the centre of the field. 



For those microscopists whose instruments are without 

 a traversing stage " Maltwood's finder " will be found an 

 efficient substitute for the one just described. This consists 

 of a glass slide, 3x1^ inches, on which is photographed a 

 scale occupying a square inch ; this is divided by horizontal 

 and vertical lines into 2,500 squares, each of which con- 

 tains two numbers marking its "latitude," or place in 

 the vertical series, and its "longitude," or place in the 

 horizontal series. The scale is in each instance an exact 

 distance from the bottom and left-hand end of the glass 

 slide ; and the slide when in use should rest upon the 

 ledge of the stage of the microscope, and be made to abut 

 against a stop, a simple pin, about an inch and a half from 

 the centre of the stage. To use this finder, the object- 

 slide must be placed under the microscope with the same 

 care as the finder ; and when some especial object, whose 

 place it is desired to record, has been brought into the 

 field of view, the object-slide being removed, the finder 

 laid down in its place, the numbers of the square then in 

 the field of view are to be read ofi" and recorded. This 

 should also be recorded upon the object-slide ; and at any 

 future time, when it is wished to refer to the same object, 



