subsequent improvement in price. Thallium has experienced a severe
depreciation on account of the economical process by which it is
extracted from the residue of the lead chambers used in the manufacture
of sulphuric acid. The use of this metal is mainly confined to
experimental purposes. The fall in silver has arisen from increased
production and diminished use for coinage.

Magnesium was scarcely of any industrial value prior to the fall in price
now recorded. Improved processes for its treatment have successfully
engaged the attention of scientific men, and it is now capable of being
used as an alloy with other metals. The Salindres factory regulates the
price to a certain extent, and its system of working is regarded as a
guide in the various processes connected with this branch of industry.
The manufacture of potassium and sodium will, it is expected, be more
fully elucidated than hitherto, by means of researches made at Schering's
Charlottenburg factory. The course of nickel prices illustrates the
stimulus to economical production afforded by an increased consumption.
This latter fact is principally due to the employment of nickel for
coinage, as alloy for alfenide, etc. The use of cadmium is materially
restricted by its relatively limited supply. Hitherto, its only source
was in the incidental products of zinc distillation, but of late it has
been attempted to bring it into solution from its oxide combinations. An
increased employment of cadmium for industrial purposes is expected to
follow.

Production in excess of the demand has caused the depreciation recorded
in tin, and various other metals not commented upon, this remark applying
even to the scarce metals, arsenic and antimony. Even the better marks of
Cornwall tin and Mansfield refined copper have had to follow the downward
course of the market.

* * * * *

A PERPETUAL CALENDAR.

The annexed figure represents a perpetual calendar, which any one can
construct for himself, and which permits of finding the day that
corresponds to a given date, and conversely.

The apparatus consists of a certain number of circles and arcs of circles
divided by radii. The ring formed by the two last internal circles is
divided into 28 equal parts, which bear the names of the week, the first
seven letters of the alphabet in reversed order, and two signs X. The
circle formed by the external circumference of the ring constitutes the
m