tjjS Dr . Wollaston's Description , &c. 
nearly parallel as may be to the milled head m, is next ren- 
dered truly parallel to the axis by turning the handle l till 
the reflected image of a horizontal line is seen to be hori- 
zontal. 
By means of the milled head /, the second surface is then 
brought into the position of the first, and if the reflected image 
from this surface is found not to be horizontal, it is rendered 
so by turning the milled head m, and since this motion is 
parallel to the first surface, it does not derange the preceding 
adjustment. 
