2 THE MICROSCOPE. Jan., 



we have made a new acquaintance and ever after when 

 we see one of them in house or garden we can say: "Now 

 I know you." These two-winged insects belong to the 

 class Diptera which is composed of twenty-eight families. 

 The house-fly, the blow-fly, the horse-fly, the mosquito 

 and others with which we are familar belong to this 

 class. 



The little house-fly (Fig. 1) is cs^Wed Muse a do?7iestica. 

 But it is now midwinter and where shall we find a fly.? 

 Go to some place where meat is sold or bo some out of 

 the way hiding place. A last summer's fly may still be 

 clinging to a spider's web or to the wall. If not dead, 

 kill it by putting it in a large-mouthed bottle contain- 

 ing a little chloroform. 



Now open the Excelsior microscope described in the 

 last number and arrange it as shown in the Dec. frontis- 

 piece, placing the flat side of the glass stage G up, and 

 the smallest of the lenses F nearest the glass stage. 

 Put the instrument near a wiudow with the mirror 

 toward the light; turn the two largest lenses so they 

 will come directly over the mirror and put the case 

 containing the small lens and the diaphram at right 

 angles to the lenses so that it will not interfere with the 

 moving of the screw in the stage. Now slant the 

 mirror so that on looking through the lenses you will 

 have a white field. Place the fly on the centre of the 

 glass stage, as though he were walking, and having 

 loosened the screw in the stage, move the stage up and 

 down very slowly until you can see the fly distinctly, and 

 then fasten the screw. This is focusing the instrument. 

 As the fly is quite tliick and the light comes to a focus 

 at one point only, you will not be able to see all parts with 

 equal distinctness, but look at the head and back first, 

 then focus again for the legs. With a little patience 

 and practice you will be able to get a good focus quickly. 



To have a microscope well lighted and in proper focus 



