floor.  The planks used as staging are 9 inches by 21/2 inches; they are moved from place to place as required, and upon them the men stand when working in the stopes and in the faces.  A stope resembles a huge chamber fitted with scaffolding from floor to roof.  The atmosphere is cool and pure, and there is no dust.  Stage is added to stage, according as the stoping requires it, and ladders lead from one floor to the other; the accessibility to all the faces is a great advantage.

If, while driving, a patch of low grade ore is met with, it can be enriched by taking a higher class from another face, and so on.  Any grade can be produced by means of this power of selection.  Opinions have been expressed that this system of timbering is not secure, and that pressure from above would bring the whole structure down in ruins.  But an opinion such as this is due to miscomprehension of the facts.  If signs of weakening in the timbers become apparent, the remedy is very simple.  Four or more of the uprights are lined with planks, and waste material is shot in from above, and a strong support is at once formed, or if signs of crushing are noticed, it is possible to go into the stope, break down ore, and at once relieve the weight.”

[Illustration:  The square system of timbering in mines.]

* * * * *

TRANSIT IN LONDON, RAPID AND OTHERWISE.[1]

  [Footnote 1:  Abstract from a paper read before the Boston Society
  of Engineers, in April, 1890.]

By James A. Tilden.

The methods of handling the travel and traffic in the city of London form a very interesting subject for the study of the engineer.  The problem of rapid transit and transportation for a city of five millions of inhabitants is naturally very complicated, and a very difficult one to solve satisfactorily.

The subject may be discussed under two divisions:  first, how the suburban travel is accommodated, that is, the great mass of people who come into the business section of the city every morning and leave at night; second, how the strictly local traffic from one point to another is provided for.  Under the first division it will be noted in advance that London is well provided with suburban railroad accommodation upon through lines radiating in every direction from the center of the city, but the terminal stations of these roads, as a rule, do not penetrate far enough into the heart of the city to provide for the suburban travel without some additional methods of conveyance.

The underground railroad system is intended to relieve the traffic upon the main thoroughfares, affording a rapid method of transportation between the residential and business portions, and in addition to form a communicating link between the terminals of the roads referred to.  These terminal stations are arranged in the form of an irregular ellipse and are eleven in number.