THE MICROSCOPE. 8 3 
“doublets” (two pieces of glass), “triplets’” (three pieces), 
““platyscopic lenses,” etc. A section of a triplet is shown 
in fig. 32. A good triplet gives a perfectly flat field and is 
free from rainbow hues around the object viewed. 
Some means of support should be devised to hold the 
simple lens. A very simple one may be made by means of 
a block of wood, two bits of stiff iron wire, and a couple of 
corks. The block of wood should be used as a base. In 
its centre one of the pieces of wire should be fixed in an up- 
right position. On this wire one of the corks should be 
Fic. 33. 
made to slide up and down freely, but not so loosely as to 
ship. Through this cork the second rod should move with 
the same freedom as the first, but at right angles ; and at its 
farther extremity, the second cork, which is shaped to hold 
the lens, should be fixed. The corks used in this way afford 
a very smooth motion and the apparatus produces good 
results. 
A rather more expensive piece of apparatus for this pur- 
pose is that shown in fig. 33, and which hardly needs any 
explanation. ‘The whole is made of brass and is especially 
adapted for the usual style of mounting triplets. The two 
