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Microscopical Essays. 101 



7 is to be placed, when the magnifiers, No. 1, 2, 3, and 4, are to 

 be ufed. 



e k is a final! piece of rack work, which is moved backwards 

 and forwards by the pinion that is fixed to the lower end of the 

 milled nut b : by the- gradual motion of this rack, the objects are 

 adj lifted to the foci of the different lenfes. 



Fig. 8 is a brafs Aider, with four or fix lenfes or magnifying 

 glades ; it is to be inferted into the hole at q ; either of the mag- 

 nifiers may be placed before the objecl, by Hiding it one way or 

 the other : you may perceive when the glafs is in the center of 

 the eye hole by a fmall fpring falling into a notch which is made 

 on the fide of the Aider oppofite to each lens. 



To use the Solar. Microscope. 



Fallen the fquare plate againfl the infide of a window-mutter,. 

 By the two fcrews O, P, which. are to go from the out: fide o£ the 

 window-lhutter through it, and then be fcrewed into their 

 refpective holes in the fquare plates G H I. The mirror is to-be 

 on the outride of the fimtter, pafling through a hole made for 

 that purpofe. 



Darken the room ; then place a fcreen at a convenient diftance 

 from the window, the farther it is from it the larger is the image : 

 now move the mirror K L by the two nuts M, N, till the fun's 

 rays come through the inftrument in an horizontal direction to 

 the fcreen, forming a round fpot thereon ; fcrew the microfcope, 

 Fig. 5,; into it's place EF; put the Aider, with the lens, Fig. 8, 

 ' I f • v' * * ■ ■ - • :J . : :•• in- 



