rature must be approximately between 50 deg. and 100 deg. F. Below
32 deg. F. and above 150 deg. F., no decay occurs.

When, therefore, wood is exposed to the weather (air, moisture, and
ordinary temperatures), fermentation and decay will take place, unless
the germs can be removed or rendered inoperative.

Experience has proved that the coagulation of the sap retards, but does
not prevent, the decay of wood permanently.[1] It is therefore necessary
to poison the germs of decay which may exist, or may subsequently enter
the wood, or to prevent their intrusion, and this is the office
performed by the various antiseptics.

[Footnote 1: Angus Smith, 1869, "Disinfectants." S.B. Boulton, 1884,
Institution Civil Engineers, "On the Antiseptic Treatment of Timber."]

We need not here discuss the mooted question between chemists, whether
fermentation and decay result from slow combustion (eremacausis) or from
the presence of living organisms (bacteria, etc.); but having in the
preceding pages detailed the results of the application of various
antiseptics, we may now indicate under what circumstances they can
economically be applied.

_(To be continued)_.

* * * * *

THE SPAN OF CABIN JOHN BRIDGE.

_To the Editor of the Scientific American Supplement:_

Your issue of 17th October contains the fifth or sixth imprint of Mr. B.
Baker's, C.E., recent address at the British Association of Aberdeen
which has come into my hands.

In speaking of stone bridges, he alludes to the bridge over the Adda as
500 years old. It was never more than 39 years old as stated in the same
address, and he belittles the American Cabin John Bridge by making its
span _"after all only 215 ft."_ As the builder of this greatest American
stone arch, I regret that on so important and public an occasion the
writer was not accurate.

The clear span of Cabin John Bridge is 220 ft. The difference is not
great, but in the length of a bridge span it is the last foot that
counts, as in an international yacht race to be beaten by one minute is
to fail to capture the cup.

M.C. MEIGS.

Washington, D.C., Oct. 16, 1885.

* * * * *

THE GERMAN CORVETTE AUGUSTA.

On the 3d of June of this year, the German cruising corvette Augusta
left the island of Perrin, in the Straits of Bab el Mandeb, for
Australia; and as nothing has been heard of her since that day, the
report that she w