(95) 
other in the space. This result appears sufficiently important to 
warrant its early publication. 
Undoubtedly there are still other influences which are caused by 
the structure of the nitrogen compounds, but in order to study these 
a great many more substances will have to be tested. The research 
will, therefore, be continued. 
Microscopy. — Prof. J. W. Morr describes: “An apparatus for 
focussing the projecting-microscope from a distance.” 
In the new Botanical Laboratory of the University at Groningen 
the lecture-room is entirely arranged for the purpose of demonstration 
by means of projecting-apparatus. I intend to describe elsewhere 
the principal features of the general arrangements. Here I will 
only mention one special point. An important part of the projecting- 
apparatus is formed by the projecting-microscope, of which the 
magnifying power is 5000 diameters and more. With such highly 
magnified images it is of special importance that any part of the 
object can be brought to a sharp focus, which cannot be done by 
a person who is at some distance from the screen, so as to be unable 
to distinguish the finest details. Moreover the demonstrator who 
stands next to the screen must be able during his explanation con- 
tinually to alter the adjustment of the fine motion-screw, for the 
same reason which necessitates this adjustement when working with 
the ordinary microscope. 
If therefore high magnifications are often used in the projection, 
the sharp focussing cannot be left to the assistant at the apparatus, 
as is generally done in projecting photographic images. It is abso- 
lutely necessary that the lecturer himself has a complete control 
over the adjusting apparatus. In the laboratory at Groningen the 
distance between the screen and the projecting-apparatus is 6 M., 
while moreover the latter is placed in a separate small room adjoining 
the lecture-room. 
The idea, which naturally first presents itself, is that of an arran- 
gement by which the adjusting-screw of the microscope can, from 
the position of the lecturer, be moved at will in either direction. 
This could be done either by electrical transfer of power’), or 
1) At the Dutch scientific and meilical congress held at Rotterdam in April 1901 
an apparatus constructed on this principle was used by Dr. W. ErnruoveN, of which 
however I have not seen the details. 
