1892.] THE MICKOSCOPE. 109 



NEWS TRO/A 

 THE WORKERS 



A Polarizing Object. — Professor E. B. Knerr of the Midland 

 College, Kansas, sends us the following : A beautiful polarizing 

 object for the microscope is made of the needle-shaped crystals 

 usually found on the surface of vanilla beans. To get the best 

 effect, a few of these crystals are dropped upon a cover-glass and 

 held in the fingers over a lamp flame until they melt. By hold- 

 ing the glass in the fingers, such a heat as would decompose the 

 crystals is prevented. When molten, the under side of the cover-^ 

 glass is moistened near the edge with saliva and placed upon an 

 ordinary slip, with the molten crystals up. The saliva causes the 

 cover-glass to adhere to the slip, and the body of the instrument 

 may be tilted without danger of its falling oft'. The preparation 

 is examined immediately. At first no polarization will appear, 

 even after the substance has solidified, but in a few seconds an 

 edge will begin to show brilHant color, and this will grow rap- 

 idly until the whole patch is exceedingly brilliant, showing at the 

 margins fine flame-like structures much like the figures we have 

 seen of the protuberances of the sun's corona. Should any of the 

 patches of the material be slow to take up the polarizing structure, 

 a slight touch with a needle or even a sudden blow on the table 

 will induce action, and when once started the change will spread 

 rapidly through the whole mass. Cover-glasses are recom- 

 mended rather than slips to receive the crystals, for the reason that 

 being thin they cool very rapidly and the experiment requires 

 much less time. After a few hours the crvstals on the gflass lose 

 their polarizing effect to a great degree, especially if exposed to 

 the moisture of the air, but they can soon be restored by again 

 melting over a flame and allowing to cool as before. 



Cleaning Homogeneous Objectives. — After one is through 

 with a homogeneous objective, it should be carefullv cleaned as 

 follows : Wipe oft^ the homogeneous liquid with a piece of the 

 Japanese paper, then, if the liquid is cedar oil, wet one corner of 

 a fresh piece in benzine and wipe the front lens ^vith it. Immedi- 

 ately afterward wipe with a dry part of the paper. The cover- 

 glass of the preparation can be cleaned in the same w^ay. If the 

 homogeneous liquid is a glycerine mixture proceed as above, but 

 nse water instead of benzine to remove the last traces. — S. H. Gage. 



