586 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
column A, and a reading of its position is taken on the divided head and 
index. 
The dry system is then replaced by the immersion system and as 
sharp as possible an adjustment is made by means of the coarse-adjust- 
ment. The screw m is then turned until it again rests on the column A. 
A second reading is taken on the divided head and index, and once 
for all the difference D is noted between the position of the micrometer 
screw m in the adjustment with the dry system and in the adjustment 
with the immersion system. In the observation of any preparation 
Fig. 90. 
Fig. 91. 
with the immersion system, adjustment is first made with the dry system, 
the screw m is turned until it touches the column, the body-tube is 
raised and m again turned through an amount equal to the difference D 
previously determined. The dry system is then replaced by the im- 
mersion system and the body-tube lowered by the coarse-adjustment 
until the micrometer screw m touches the column A. For the perfectly 
sharp adjustment only a very slight movement of the ordinary micrometer 
screw of the stand will then be required. The ajiparatus is easily 
detachable from the stand, when not required. 
