4 11 
how many divisions ( e.g ., two) any body (e.g. a blood 
cell) covers, and multiply by 4 the value 5 of each 
eyepiece scale for this combination of lenses. This 
method is more accurate than the following. 
Method II .—It is necessary to have a camera lucida 
(the upright pattern is most convenient). Adjust 
the light of the mirror and the diaphragms of the 
camera lucida so that the object and the tip of the 
drawing pencil are both clearly seen. Mark out the 
required dimensions of the object, e.g., length and 
breadth, on the paper placed at the right-hand side 
of the microscope, using the right eye for observing. 
Now place a millimetre scale divided into hundredths 
on the stage instead of the object. Draw the scale 
on the paper just below the object. Read off 
directly the size of the object in millimetres. The 
smallest amount that can be measured is riio mm. = io/u 
Note. —By measuring the magnified size as drawn and dividing 
this by the actual known size of the stage micrometer the magnifi¬ 
cation of the microscope is given. 
Weights and Measures, etc. 
. i. Conversion from one Temperature Scale to 
another .— 
C _ F- 32 
5 9 
Thus to convert ioo° F. to centigrade- 
100 - 32 _ C 
9 ~~S 
c = 377 ‘ 
2. Formula for Dilution of Solutions.- —The number 
of parts required to dilute from one part of a solution 
of strength x per cent, to another strength y per cent. 
. x 
is - - 1. 
y 
