162 Intelligence and Miscellaneous Articles. 
in eleven columns, were illustrative of the range of the respective 
species and varieties in different zones of sea-depth, from the shore 
to 1700 fathoms, and of the relative size of the individuals, and of 
their proportional paucity or abundance. Among the seventeen 
columns of fossil Foraminifera, some were very rich in species and 
varieties, especially in the case of the Siennese clays, the Malaga 
clay, and the Vienna basin. From the evidence afforded by the com- 
parison of the fossil with the recent Foraminifera, the Siennese blue 
clays of S. Cerajolo, S. Donnino, 8. Lazaro, and Coroncino were 
regarded as having been deposited in various depths of from 40 to 
100 fathoms; so also the clay-beds of Malaga and of the Vienna 
basin. A blue clay from S. Quirico was probably formed in about 
200 fathoms; a blue clay from Pescajo, on the contrary, was the 
deposit of a shallow estuary. A sand from Pienza, and others from 
Montipoli, Castel’ Arquato, and San Frediano, contain Amphistegina, 
and were probably deposited in from 10 to 20 fathoms water. As 
the Amphistegina appears now to be extinct as regards the Medi- 
terranean, these Amphistegina-beds, and others at Palermo and in 
the Vienna Basin, may be of miocene age. Another Siennese clay 
from Monti Arioso is of shallow-water formation. From Turin some 
shelly sands, of pliocene age, were defined as containing a group of 
Foraminifera similar to those now living on the western shores of 
Italy; and the Palermo deposits are, for the most part, not very 
dissimilar. The Heterostegina-bed at Malta, formed probably in 
rather shallow water, is characterized by a species now absent from 
the Mediterranean. The tertiary deposit from Baljik appears to 
have been a shallow-water deposit, characterized by some forms 
peculiar at the present day to the Red Sea,—a condition that is also 
indicated by some of the Viennese deposits. 
XXI. Infelligence and Miscellaneous Articles. 
OPTICAL LECTURE-EXPERIMENTS. BY PROF. KNOBLAUCH. 
ID I not hope to furnish my colleagues with a few welcome 
experiments for the lecture table, I should scarcely venture 
to occupy these pages with a communication which involves nothing 
but what has been long well known. 
Optical lenses have been so universally constructed of substances 
whose indices of refraction exceed that of the surrounding medium 
(such being alone useful in practice), that, accustomed to the pheno- 
mena dependent thereupon, we unconsciously associate convergent 
effects with convex, and divergent ones with concave lenses. 
In order strikingly to illustrate by experiment the influence which 
here, under the same form of the limiting surfaces, the enclosed 
medium exerts, I introduce, in my lectures on experimental physics, 
experiments with hollow lenses so composed of plane glass discs and 
watch-glasses, that the one forms a plano-convex, the other a plano- 
concave lens*. 
* The radius of curvature here is about 116 millims.; the aperture of 
the setting has a diameter of about 64 millims. 
