( 96 ) 
mechanically by a connecting rod or by means of so called “flexible 
tubing’, such as is used in boring apparatus of different kinds, e. g. 
by dental surgeons. 
In the present case however there is an objection to such a solution 
of the problem, viz. the bad construction of the adjusting-serew of 
the projecting-microscope. The projecting apparatus used at Groningen 
was made by the well known firm Newron & Cy., London. It 
is of excellent design +) and is, according to my experience, pref- 
erable to others. A great drawback however is that the workman- 
ship of the metallic parts is not always of the highest standard. 
Thus especially the screw for the fine adjustment is far inferior in 
quality to what is generally found in modern microscopes. 
In the case of high magnifications and with a distance of the 
sereen of 6 M. extremely minute alterations of this distance corre- 
spond to large differences in focussing. No satisfactory result could 
thus be expected in this way. Also it proved to be very difficult 
to replace the bal screw by a better one. 
Thus I was led to another solution of the problem which appears 
to me to be very simple and effective. It is well known that by 
changing the distance between the ocular- and objective-glasses in 
an ordinary microscope, different levels of the object can be brought 
to a sharp focus. In this way the same end is obtained as by turning 
the adjusting-screw, and even somewhat better, as a motion of the 
ocular is equivalent to a considerably smaller motion of the screw. 
Consequently in the ordinary microscope a more exact focussing 
can be effected by means of the ocular-glass than by the adjusting- 
screw. 
RANVIER”) mentions that he has an arrangement fitted to his 
microscope by which a fine motion can be given to the ocular. 
This arrangement is used in delicate observations. 
Naturally the same principle can be applied to the projecting- 
microscope, and some preliminary experiments at once gave very 
satisfactory results. 
At first a wooden cross-beam was fixed before the microscope, and 
entirely free from it. The objective only was left on the microscope, 
the ocu'ar being fixed on a wooden slide, or sledge, which was so 
connected to the cross-beam, that it could be moved through about 
De. f. Lewis Wricut. Optical Projection. London 1891. This I think is the best 
work which has been written about methods of projection. The author is also the 
designer of the microscope by Newron & Cy. 
*) Ranvier Technisches Lehrbuch. 
