THE MICROSCOPE. 
1-12” = 120. This is called the initial magnification in microscope 
objectives.’ The eye-pieces are magnifying glasses, and magnify the 
enlarged image formed by the objective. Hye-pieces generally magnify 
from 2 to 12 times. Though higher than this are made, they are not 
recommended, except the type known as compensating oculars. The 
amount of magnification used in most work does not exceed 1,500 times, 
such as can be obtained by a 1-12” or 1-16” focus objective, called an 
oil-immersion objective (because the end of the lens dips into cedarwood 
oil, which fills up the space between the lens and the object under 
observation), with a 10 or 12 eye-piece. Higher magnification 
with more detail may be obtained by using the best corrected objectives 
(apochromatic) with compensating oculars. The eye, however, limits 
the amount of detail that can be observed, and very high magnifications 
do not increase the amount of detail, but makes it larger only. The 
magnifications given are only approximate, however, as different makers 
select different visual distances, and consequently different tube lengths 
for their microscopes. These vary from 160 mm. (8 inches) to 250 mm. 
(10 inches), and when using any particular make, the length of tube 
extension should provide for the exact tube length recommended by the 
maker, or his lenses will not give their best results. 
The unit of measurement in microscopy is the micron, represented 
by the Greek letter Mu — pp. This is equal to .001 of a millimetre, or 
1,000 «} = 1mm. Since a mm. = 1-25 part of an inch, a micron 
= 1-25,000 of an inch. The smallest bacteria that are visible with the 
ordinary method of examination are about .12 u or 2 of a micron in 
size (e.g., the Influenza bacillus), 7.¢., about 1-200,000 of an inch long. 
Objects smaller than this have to be examined by special apparatus 
and special methods of illumination. Most microscopic work, however, 
except bacteriology and kindred work on other parasites, is performed 
with magnifications not greater than 600 times an amount obtainable with 
objectives not greater than 4” focus, and using an eye-piece magnifying 
not more than 10 times. 
oO —— 
There are many reasons why agricultural research should 
form a prominent feature of the activities of the Commonwealth 
of Australia, Its ultimate aim is to increase the productivity 
of the country, and it would be impossible to exaggerate the 
importance of that at the present juncture; for, when the war 
clouds have passed away, when men have beaten their tanks 
into tractors and their bayonets into binder-blades (to modern- 
ize a scriptural quotation), and peace once more comes to this 
troubled world, there will be a huge bill to pay, and that bill 
can only be paid as the result of increased—and greatly 
increased—production. ; 
—Professor R. D. WATT. 
5OU 
