GL 
tion band surpass 180°. The interior interference fringes are very 
indistinet. Their appearance would suggest that in the case of D, in 
Fig. 4 the stage has been scarcely surpassed, reached for D, in fig. 2. 
This however cannot be the case because there was too much 
sodium in the flame. A comparison with fig. 2 will show that the 
lines are much broader in fig. 4. Measurements taken on other 
negatives gave me for fields of 11000, displacements of about ‘/,, of 
the distance between two fringes, corresponding to a positive rotation 
of 11°. Hence the displacements in these eases are precisely of the 
same order of magnitude as in CorBiNo’s experiments. The paleness of 
the boarders of the band is easily accounted for by the remark that there 
the intensity one of the circularly polarised rays largely exceeds the other. 
I do not believe that these facts are in contradiction with theory. 
It is true that it requires for very high values of P a value zero for 
Wy), If we must take as the locus of the fringe the mean vertical 
height, then really the rotation would be positive. It seems possible 
that with those broad fringes the case is different. It is also possible 
that the circumstances, assumed in the theory are not wholly realised 
in the experiments with dense vapours. 1 am making some new expe- 
riments about this subject and therefore shall not discuss further the 
different possibilities. 
EIA NATEON, OF THE PLATE. 
The Plate gives about sixfold enlargements of the photographs. 
Wig. 1. Interference fringes and absorption liaes in absence of the field and 
rather much sodium. (2) 
Fig. 2. Same lines. Field intensity about 14000, little sodium. (3) (5) 
Fig. 3. Same lines. Field intensity about 4500, much sodium. (8) 
Fig. 4. Same lines. Field intensity about 10700, much sodium. (8) 
Anatomy. — “A new Method for demonstrating cartilaginous 
Mikroskeletons.! By Prof. J. W. van Wise. 
It is a well-known quality of cartilage that it firmly retains certain 
anilinstains. Taking advantage of this quality, I have for some years 
endeavoured to find a stain, which will remain permanent in the cartilage, 
after it will have been entirely extracted out of the other tissues. 
If the object is made transparent in canada balsam, the cartilaginous 
skeleton will then be seen as if it were prepared. I was more or 
less successful with most of the so-called basal anilin-pigments, best 
of all however with methylene-blue, and so I was induced to use this 
latter stain exclusively, 
