then each pair of opposite elements b;, « meets the lines of the 
conjugate quintuple (vi), from which ensues that the pairs of 
planes (Pbi), (Pei) do so likewise. So we have proved the following 
theorem: 
Through any point P two planes (fi, yi pass cutting 
the lines of the conjugate quintuple (wi). The six pairs 
of planes we vs, (C= 1, 272 00), and the fiiteemsplame: 
connecting P with the lines of the configuration are 
cut by an arbitrary space not passing through P accor- 
ding to the 27 right lines of a same surface of class 
three. 
Of the lines cutting four arbitrary planes @,@,@3,@, given in 
S, two lie in an arbitrary space S's; for this space cuts the four 
given planes according to four crossing lines, which admit of two 
common transversals. By dualistic reversion it ensues from this, 
that through an arbitrary point P two planes pass cutting any 
four given lines aj, ag, a3, a, And then the above mentioned 
theorem teaches us that the connection among the five conjugate 
lines a; is also expressed by the circumstance, that each plane cutting 
four of the five lines also cuts the fifth. This characteristic property 
forms the starting point of Dr. SEGRE’s considerations. 
In the second part of this communication will be indicated how 
the analytical representation of the fifteen planes can be simplified; 
so I will have occasion to show the relation of my results to two 
studies of Dr. G. CASTELNUOVO, of the existence of which I was 
not aware in the moment this first part was passing through the press. 
Chemistry. — Professor Lopry DE BRUYN presents a dissertation 
from Dr. N. SCHOORL and a communication on: “ Urea deri- 
vatives (carbamides) of sugars’. II. 
In continuation of the first communication (see report of 29 Dec. 
1900) the following has been taken from the said dissertation. 
The method of determining the molecular weight by means of the 
increase in the boiling point gave unsatisfactory results with glucose- 
ureide because, as was shown afterwards, this is decomposed by 
