460 Proceedings of Philosophical Societies. (June, 
faces, so that the edges are also curvilinear. In order to cut glass, 
a diamond of this form requires to beso placed that the surface of 
the glass is a tangent to the curvilinear edge, and equally inclined 
laterally to the two adjacent surfaces of the diamond. Under these 
circumstances the parts of the glass to which the diamond is applied 
are forced asunder, as by an obtuse wedge, to a most minute dis- 
tance, without being removed; so that a superficial and continuous 
crack is made from one end of the intended cut to the other. After 
this any small force applied to one extremity is sufficient to extend 
this crack through the whole substance, and successively along the 
whole breadth of the glass. For since the strain at each instant of 
the progress of the crack is confined nearly to a mathematical line 
at the bottom of the fissure, the effort necessary for carrying it 
through is proportionally small. He found by trial that the cut 
caused by the mere passage of the diamond need not penetrate so 
much as =1. of aninch. Other mineral bodies recently ground 
into the same form possess the same property, but soun lose it. 
On Thursday, May 9, a paper by William Chapman, Esq. 
M.R.I.A. on the probable formation of mineral coal, and on the 
position and accompanying circumstances of fossil trees, was read. 
He was led into the train of reasoning exhibited in the paper by 
viewing several of the casts of trees so common in the sandstone 
which accompanies the coal in Northumberland. These casts are 
composed of sand-stone, and are surrounded with a layer of charry 
matter, which is conceived to have been the bark of the tree. 
Similar trees in the same position occur in peat bogs. From this, 
and from the remains of reeds and other similar vegetables common 
in the coal beds, Mr. Chapman conceives that the coal originated 
from peat beds, and that it acquired its present consistency and 
compactness from compression. He enters into several calculations 
to show the degree of compression that would be necessary to pro~ 
duce the effect, and conceives that by the action of matter in fusion 
on the top of the beds, the charring may have been produced re~ 
quisite to convert the coal into Kilkenny coal and Welch culm. 
On Thursday, May 16, a paper by Mr. Morney was read, de- 
scribing a mass of meteoric iron found by him in Brazil in the year 
1810. At that time a pretty strong chalybeate was discovered not 
far from the seat of Government. This discovery was considered as 
important, and induced the Prince Royal of Portugal to request Mr. 
Morney to take a journey to examine some thermal springs which 
had been announced as existing several years before at the distance 
of about 50 leagues from Bahiar. As a further inducement to 
undertake this. journey, he was told of a remarkable stony mass 
which had been observed at no great distance from the thermal 
springs. This body had been first remarked by a shepherd.. The 
superintendent of the neighbouring district was sent to examine it. 
His report was so wonderful that orders were given to remove the 
stone, and bring it to the seat of the Court. The attempt was 
made, It was raised upon an ill-constructed carriage, and 40 pair 
