Till: MICROSCOPE AND ITS ACCESSORIES. 



20. Malasse/'s Camera placed at a 

 variable angle. 



desired to incline the microscope at an angle of 45 (fig. 20), the 

 camera is so placed that an image is thrown on paper placed behind 

 the foot of the microscope, the prism being turned to an angle of 

 45. This camera is particularly 

 easy to work with. It is some- 

 times important not to have too 

 much light on the paper ; this is 

 avoided by using the plane side of 

 the mirror. 



16. Magnifying Power of a 

 Microscope. This will vary with 

 the objective and ocular used, and 

 also with the length of the draw- 

 tuhe. The magnification is usually 

 determined when an image is seen 

 at the range of normal distinct 

 vision, i.e., 10 inches or 25 centi- 

 metres. As this is about the 

 height of a Hartnack's stand or 

 Zeiss's stand, supposing these 

 forms of instrument to be used, 

 place a sheet of white paper on 

 the table. Let the microscope be upright, with ocular and lens in 

 place. Supposing we use a No. 7 objective and No. 3 ocular. 

 Begin with the draw-tube in, place a stage-micrometer on the stage 

 of the microscope, and focus the scale upon it. The stage-micro 

 meter is like a glass slide with a fine scale engraved upon it. The 

 English ones are generally subdivided into thousandths of an inch, 

 and the Continental ones into hundredths of a millimetre. Look 

 through the microscope, but keep both eyes open, and part of the 

 scale will be seen on the white paper. With a pencil mark off sny 

 ten interspaces, or use a pair of compasses to measure this distance. 

 Measure off this distance on a millimetre scale, and suppose the 

 distance thus measured be 28 millimetres. This means that .1 

 millimetre has been magnified to appear equal to 28 millimetres, 

 />., 280 times. The magnifying power for other combinations of 

 lenses should be determined, and a table made for future reference 

 and use. 



Magnifying Power. This may be increased 



(a) By using a higher objective. 

 (f>) By using a higher eye-piece. 



(<) By pulling out the draw-tube and increasing the distance 

 between the objective and the eye-piece. 



Construct a table according to the following scheme of the 



