( 203) 
chromosphere gases. Now we can hardly assume that these gases 
really do not emit any light; the question is only, in what cases 
and how far the intensity of the true chromospherie emission is compar- 
able with the intensity of the abnormally refracted photosphere light. 
Perhaps the photographs obtained by our expedition are acciden- 
tally so extremely fit to show the part played by anomalous dispersion 
in causing chromosphere light, that they induce one to overestimate 
the importance of the new principle. 
It would therefore be very interesting if the plates of other 
expeditions were also studied from this point of view. 
Mathematics. — “Considerations in reference to a configuration of 
Srere”’. By Prof. P. H. Scuoure (first part). 
1. In a treatise published in 1888 “Sulle varietà cubiche 
dello spazio a quattro dimensioni, ecc” (Memorie di Torino) 
Dr. C. Srare proved the following remarkable theorem: 
The locus of the right lines cutting any four planes 
assumed in the space S, is a curved space of order 
three containing besides these four planes eleven 
planes more; one of these eleven new planes is inter- 
sected by all the right lines cutting the four given 
planes. The fifteen planes pass six by six through 
one of ten points, which are double points of the 
cubic locus. 
If we call the four given planes a@,/f,y,0 and if we 
denote by @ the plane through the three points of 
intersection (y0), (0/2), (77), by / the plane through the 
three points of intersection (da), (ey), (yo), ete., then the 
four points of intersection lie in one and the same 
space « and the five planes form such a quintuple, 
that each right line cutting four of these planes, also 
cuts the fifth. 
In a study also published in 1888 “Alcune considerazioni 
elementari sull’ incidenza di rette e piani nello spazio 
a quattro dimensioni” (Rendiconti del circolo matematico di 
Palermo, vol. 2, pages 45—52) the same writer gives a rather 
simple geometrical proof of the second part of this theorem, and 
then ascends to the configuration mentioned in the first part by the 
indication that the ten points spoken of are the points of intersection 
of the five planes a, 7,7,0,¢ two by two and the ten new planes 
