126 THE MICROSCOPE. Aug. 



PRACTICAL SUGGESTIONS. 



By L. a. WILLSON, 



CLEVEL\ND, OHIO. 



Projection and Measurement. — The microscope may be 

 used as a ma.dc lantern for projecting pictures upon the wall. 

 To accomplish this, place a sheet upon the wall to receive the 

 picture. Put the microscope in a horizontal position. A lamp 

 like the Acme with shade and bull's-eye will best effect the ob- 

 ject ; in the absenc ", of such a lamp, smoke the inside of a lamp 

 chimne}^ and make a small vertical slit to permit the passage of 

 a pencil of light. A bull's-eye should be interposed between 

 the scope and the lamp with this blackened chimney. 



Darken the room and objects may thus be easily projected 

 upon this suspended sheet. Some objects will be much more 

 brilliant than others. 



A little practice will determine the best distince for placing 

 the microscope from the sheet. In a similar manner, as stated 

 in Carpenter's Seventh Edition by Dallinger, " the simplest 

 mode of measuring minute objects is to project the magnified 

 image of the object, then careiully trace an outline of the image 

 and without disturbing any of the arrangements, remove the 

 object from the stage and replace it with a stage-micrometer. 



Trace now the projected image of this upon the same paper, 

 and the means are at once before us for making a comparison 

 between the object and a known scale both being magnified to 

 the same extent." The same result may be more convenientl}^ 

 effected by projecting the image of the object and micrometer 

 scale upon the ground glass plate of a photographic camera. 

 Any sort of camera will suffice if left tight. 



This latter method is described on page 233 of Carpenter and 

 is there said "to make the mostaccurate measurement of which 

 the microscope is capable." 



The same results and the same projection of images may be 

 produced with the camera-lucida. 



Mounting Diatoms. — Upon a clean cover-glass, previously 

 placed upon a bronze or iron table, are dropped from a pipette 

 several drops of distilled water. Tlien from the bottle in which 



