152 



MEMORANDA. 



There is no necessity for ruling the slides. The scaling is 

 simple, and the cost ol" the instrument is very trifling. 



Box-rijood Finder, witli Lone centrepiece, in situ. 



'Ihe dotted ring shows tlie rabbet on which the centreiaiece rests. 



a, brass pin attached to centrepiece. 



b, two brass pins for steadying the instrument against the left side 



of tlie microscope stage. 

 N.B. — I'he scales may be ruled on brass or bronze and inlaid, and 

 liorizontal lines might be ruled on the surface of the instru- 

 ment as a guide for placing the slide. 



The following directions for its employment will be sufficient. 

 1st. Place the instrument on the stage, and find the central 

 needlehole through the microscope. 2ndly, Remove the bone 

 disk with the forceps held in the right hand. 3rdly. Place 

 the slide on the wood (the named side always to the right), 

 and make the requisite movements with the left finger and 

 thumb, 7iot with the stage screws. 



The position of any object occupying the centre of the 

 field will now be accurately marked by the sides and ends of 

 the slide on two, at least, out of the four scales, and can be 

 registered with a diamond point on the glass. 



To find the object again is of course extremely simple — 

 find your centre before removing the disk, and then place 

 your slide according to the letter and number marked on it. 

 As the boxwood should be at least an eighth of an inch in 

 thickness, it would be an easy matter to excavate a space 

 3 inches by 1 incli on its under side for safely stowing away a 

 slide in case of transmission by post or parcel. 



