418 
SUMMARY OF CURRENT RESEARCHES RELATING TO 
vibrate. A screw V traversing obliquely the shoulder of the movable 
branch, presses on the terminal part, and bending the steel plate raises 
the obj ‘ctive, which thus describes a small circular arc from front to back. 
Calculation shows that the harmful effect on the image of this angular 
displacement is quite insignificant. Thus, let Z be the vertical distance 
between the ax:s of rotation and the object under examination, L the 
Fio. 49. 
3 
distance of the axis of rotation to the real image of the object formed by 
the objective, d the distance of the object to the axis, and D the distance 
of the real image to the axis. Then d = hi / L. But Z is approximately 
the length of the objective for all high magnifications ; it is equal to 
about 30 mm. for a homogeneous-immersion objective ; L is the distance 
of the base of the objective to the diaphragm of the eye-piece, i. e. about 
150 mm. The ratio Z / L is therefore about 1/5. At the most, D rarely 
exceeds 1 mm. when the objectives are screwed directly on the body-tube. 
This gives to d a value of 1/5 mm. On the other side, if a denote the 
angle through which the axis of the objective has turned, we have 
tan a = -=- = = 0-00566, 
l 1 ou 
which gives for a a value less than 0 C 23'. 
