PROCEEDINGS OF THE SOCIETY. 
387 
the dispersive powers of these new media with those of some well-known 
glasses, with the following result. 
Refractive Indices and Dispersive Powers of Various Substances , 
Lines C, D, Hy. 
Glasses : — 
H-D 
M-l 
5 fi 
Chance’s light flint 
.. 1-574 
25-9 
„ dense „ 
1-620 
22-6 
„ extra dense flint 
1-640 
20-9 
,, double extra dense flint 
1717 
18-1 
Densest flint in Jena catalogue 
1-963 
11-8 
Mr. Madan’s Measurements of New 
Substances : — 
Methylene di-iodide and phosphorus . . 
1-95 
15-8 
Quinidine 
1-602 
14-0 
Methylene di-iodide 
1-743 
12-0 
Phenylthiocarbimide .. 
1-654 
10-7 
Piperine and balsam 
1-657 
5*1 
Piperine .. 
1-681 
4-8 
From this table we see that while the refractive index of methylene 
di-iodide and phosphorus is nearly equal to that of the Jena densest 
flint, it has less dispersive power ; but on the other hand quinidine, 
which has a refractive index between the light and dense flint of Chance, 
has a dispersive power nearly equal to the double extra dense flint. 
The next two in the list have high dispersive powers, but they are quite 
surpassed by piperine. 
For example, piperine and balsam has a refractive index very similar 
to Chance’s extra dense flint, but its dispersive power is four times as 
great. Piperine alone has less refractive index than the double extra 
dense flint, while its dispersive power is 3J times as much. 
On the motion of the President a hearty vote of thanks was given 
to Mr. Madan for his very valuable paper, a hope being expressed that 
something of permanent character might result from what they had 
heard that evening. 
The President said he was sure the Fellows of the Society would 
feel greatly indebted to Mr. Morland for the beautiful diatoms which he 
had brought to the meeting for exhibition. The important work he had 
done in this direction was so remarkable that it was a great pleasure to 
have an opportunity of seeing such a number of specimens. He hoped 
Mr. Morland would favour them with some description of what he was 
exhibiting. 
Mr. Morland said it had been suggested to him that he should read 
a few notes on the specimens exhibited ; but on consideration he thought 
it would be better if he wrote out a short description of each and placed 
it by the Microscope under which each specimen was shown. These 
slides were arranged, not with a view to their being test diatoms, but 
simply to show the various forms which diatoms assumed. He found 
there was in the whole collection only one of the Naviculoid diatoms. 
He did not know that he need say any more, but he hoped that the 
written descriptions would enable the exhibits to speak for themselves. 
He would, however, take that opportunity of thanking Messrs. Beck for 
