the female generative organs--Showing how
the breathing powers may be developed.--The effects of adequate
respiration in special cases.

Vital Discoveries in Obstructed Air and Ventilation.

IV. ELECTRICITY.--The Portrush Electric Railway, Ireland.--By Dr.
EDWARD HOPKINSON.

The Thomson-Houston Electric Lighting System.--4 figures.

A Modification of the Vibrating Bell.--2 figures.

V. CHEMISTRY.--Acetate of Lime.

Reconversion of Nitroglycerine into Glycerine. By C.L. BLOXAM.

Carbonic Acid and Bisulphide of Carbon. By JOHN TYNDALL.

VI. AGRICULTURE AND HORTICULTURE.--Propagation of Maple Trees.

Dioscorea Retusa.--Illustration.

Ravages of a Rare Scolytid Beetle in the Sugar Maples of
Northeastern New York.--Several figures.

The Red Spider. 4 figures.

Japanese Peppermint.

VII. NATURAL HISTORY.--The Recent Eruption of Etna.

The Heloderma Horridum.--Illustration.

The Kangaroo.

VIII. ARCHITECTURE.--Design for a Villa.--Illustration.

IX. BIOGRAPHY.--William Spottiswoode.--Portrait.

X. MISCELLANEOUS.--Physics without Apparatus.--Illustration.

The Travels of the Sun.

FARCOT'S IMPROVED WOOLF COMPOUND ENGINE.

In a preceding article, we have described a ventilator which is in use
at the Decazeville coal mines, and which is capable of furnishing, per
second, 20 cubic meters of air whose pressure must be able to vary
between 30 and 80 millimeters.

In order to actuate such an apparatus, it was necessary to have a
motor that was possessed of great elasticity, and that nevertheless
presented no complications incompatible with the application that was
to be made of it.

In the ventilation of mines it has been demonstrated that the
theoretic power in kilogrammes necessary to displace a certain number
of cubic meters of air, at a pressure expressed in millimeters of
water, is obtained by multiplying one number by the other. Applying
this rule to the case of 20 cubic meters under a hydrostatic pressure
of 30 millimeters, we find:

20 x 30 = 600 kilogrammeters.

In the case of a pressure of 80 millimeters, we have:

20 x 80 = 1,600 kilogrammeters.

If we admit a product of 50 per cent., we shall have in the two cases,
for the power actually necessary:

600
---- = 1,200 kilogrammeters, or 16 H.P.
0.05