MICROSPECTROSCOPE 
135 
sary to remove the tube A carrying the prism.^ The slit ^ is 
opened to its full width and the microscope focused in the usual 
manner, the eyepiece having first been itself focused by means 
of F and set at the proper calibration reference mark c. 
Before the instrument can yield scale readings convertible 
into wave lengths, it must be calibrated. This will necessitate 
placing upon its tubes certain reference or indicator marks. 
The instrument is removed from the microscope tube M, pointed 
toward the sky and the slit narrowed. The spectrum should 
appear as a long rectangular band of colored light crossed by 
many fine black lines at right angles (Fraunhofer’s lines) to its 
length. Should these lines appear inclined, the tube A must 
be turned slightly until they are made normal to the spectrum 
length. Having thus carefully adjusted the prism to the proper 
position with reference to the slit, make the reference marks h 
upon A and upon r in order to fix this position. Now carefully 
focus the spectrum by means of F, using the narrowest slit 
possible until the Fraunhofer lines appear sharpest. This should 
be done on a bright sunny day. Scratch the mark c to indicate 
this position. Turn t and tip the mirror n so as to reflect light 
into the tube and move L until a bright sharp white triangle 
is seen when looking into the eyepiece. Carefully turn the cap 
carrying the measuring device until the apex of the bright tri¬ 
angle takes a position just a trifle above the center of the spec¬ 
trum band. This position is easily ascertained by pushing the 
comparing prism in place beneath the slit; half the spectrum will 
now disappear. The most convenient position for the bright 
spot of light is when the base of the triangle falls just below the 
dividing fine. Make the marks indicated at a so as to fix this 
position. The instrument is now ready for calibration. It can 
be taken apart at any time and the parts replaced so as not to 
alter the values of the scale divisions. After calibration, if, at 
any future time, wave length measurements are required, the 
* In other forms of microspectroscopes, as, for example, those manufactured by- 
Zeiss, Leitz and others, the Amici prism is so mounted as to swing upon a hinge 
above the eye lens. This greatly simplifies adjustments. Unfortunately all of 
these instruments have measuring devices too crude to be of value to the chemist. 
