Dr Wollaston's Microscopical Doublet. 327 



ed to contain the instrument, which thus forms a support. A 

 portion of the tube above this piece is cut away, as marked by 

 the dotted line, for the purpose of admitting light to the small 

 mirror which is attached to an horizontal axis passing through 

 the diameter of the tube. The inclination of this mirror may 

 be varied by means of a milled head fixed to the axis on the 

 outside of the tube ; the other adjustment at right angles be- 

 ing made by turning the box of the microscope. I 



Into the tube above the opening a conical piece is soldered, 

 into which is screwed a small cylindrical tube carrying the 

 perforation before described. The plano-convex lens is fixed 

 in a spring tube, which slides into that which forms the body 

 of the microscope. The position, consequently, of the lens 

 may be varied so as to bring the image of the perforation into 

 the same plane with the object to be viewed. A jiiece of plate 

 glass about two inches square, or less if it be thought more con- 

 venient, is attached to the top of the tube, and serves to support a 

 stage having lateral adjustments at right angles to each other. 

 The piece into which the magnifiers fit, may be moved by a rack 

 and pinion, and great care must be taken to arrange this ad- 

 justment, so that the magnifier may move precisely in the pro- 

 lono^ation of the axis of the tube. The tube is divided into 

 two pieces, of equal lengths, which screw into each other, and 

 which when taken asunder will allow of the whole instrument 

 being packed in a box about four inches square. 



Supposing the plano-convex lens to be placed at its proper 

 distance from the stage, the image of the perforation may be 

 readily brought into the same plane with the object, by fixing 

 temporarily a small wire across the perforation with a bit of 

 wax, viewing any object placed upon a piece of glass upon the 

 stage of the microscope, and varying the distance of the per- 

 foration from the lens by screwing its tube until the image of 

 the wire is seen distinctly at the same time with the object upon 

 the piece of glass. 



