Page:Proceedings of the Royal Society of London Vol 59.djvu/181

If we take the differences between 1 and 4, 2 and 5, 3 and 6, we get the following four sets of values for a, b, c, and d.

	P.			Q.
Difference between	a.	b.	c.	d.
1 and 4 ......	212	211	210	212
2 and 5 ......	211	211	212	212
3 and 6 ......	211	212	212	212
	634	634	634	636

Mean = 634.5.

$\scriptstyle {i={\frac {634\cdot 5}{6\times 3}}=35\cdot 25,\quad \mu =1\cdot 733}$.

From the results given above it would appear that the index of refraction of sulphur is very near 1·73.

The method adopted thus seems to be capable of giving accurate results; no large quantity of material is required. The method is also well suited for liquids.

The determination of the indices of other solids and liquids are in progress. I shall give an account of these in a future communication.

II. "Researches on the Structure, Organisation, and Classification of the Fossil Reptilia. Part X. On the complete Skeleton of an Anomodont Reptile (Aristodesmus Rütimeyeri, Wiedersheim), from the Bunter Sandstone of Reihen, near Basel, giving new Evidence of the Relation of the Anomodontia to the Monotremata." By H. G. Seeley, F.R.S. Received November 7, 1895.

(Abstract.)

With the co-operation of the Trustees of the University Museum of Basel and Professor Rütimeyer, the author has examined the fossil described by Dr. Robert Wiedersheim in 1878 as Labyrinthodon Rütimeyeri. The bones are differently interpreted:—

The reputed humerus is the interclavicle.

The reputed scapula is the humerus.

The reputed supra-scapula is the left coracoid.

The reputed supra-scapula is the right scapula.

The reputed right and left coracoids are the pre-coracoid and coracoid of the right side.

The reputed clavicles are the ribs.

Five digits are identified in place of four in 1878.