134 SEVENTH REPORT—1837. 
is the same, the thrust is as the square of the radius for the same 
angle of the semi-arch. The paper was accompanied by diagrams 
illustrating the manner of experimenting on the arch, and with tables 
showing the agreements betwixt the theoretical and the practical con- 
clusions. 
In connection with his researches on the theory of the arch, the au- 
thor has instituted experiments to determine the greatest number of 
voussoirs which could be made to stand in the form of a circular arch. 
On the Quality of Iron for Railways. By D. Musuer. 
Respecting the qualities most essential for railway iron, Mr. Mushet 
premises the following remarks :— 
1. That a crystalline arrangement of the fracture of bar iron is 
incompatible with great strength and fibre, and that it is essential to 
railway iron that it should be hard and fibrous. 
2. The more frequently iron is heated or melted in the course of its 
completion as bar iron, the greater is its tendency to crystallize and 
become brittle whea cold. This is in some measure prevented by 
repeated rollings ; but fibre acquired in this way is, to a certain extent, 
artificial ; for where native fibre is absent, heating and cooling will re- 
store the crystalline arrangement and weaken the tenacity of the iron 
when cold. 
3. Excessive decarbonization, commonly called refining, which tends 
to deprive the iron of its last portion of carbon, produces a quality of 
malleable iron, soft, and easily abraded by rubbing or friction; and 
therefore, in point of durability, not well calculated for rail iron. 
4. Conversely, iron manufactured so as to retain the last and con- 
sequently the most intimately united portions of carbon, or to have 
this substance communicated to it in minute portions in working, is 
better caleulated, provided the fibre is not injured, for rail-making on 
two accounts, because it will wear less by rubbing, and be subject to 
less waste from oxidation. 
5. Bar or malleable iron has a tendency to crystallize in the cooling, 
in proportion to the size of the manufactured mass; a circumstance 
deserving the greatest consideration on the part of the engineer in de- 
termining the form or shape of his rails. 
6. Continued vibration, such as is produced by the motion of an 
engine or waggon travelling on a railway, causes iron to crystallize 
and to a certain degree become brittle. Hence the importance of 
making rails from iron full of fibre, so as to postpone the tendency to 
crystallization to as remote a time as possible. 
7. Unless abridged or destroyed, by the repeated heatings and fusions 
to which iron is subjected in its various manipulations, the quantity 
and strength of fibre developed will mainly depend upon the degree or 
proportion of carbonaceous matter originally contained in the pig iron 
from which it has been manufactured. 
8. It is essential in rail-making to have a quality of iron that will 
