d for the night,
but a gale caused it so much damage that it had to be broken up. It had
achieved a speed of 30 feet per second with the motors developing only
36 horse-power and, gathering from this what speed might have been
accomplished with the full 170 horse-power, Zeppelin set about the
construction of No. 3, with which a number of successful voyages were
made, proving the value of the type for military purposes.

No. 4 was the most notable of the early Zeppelins, as much on account of
its disastrous end as by reason of any superior merit in comparison with
No. 3. The main innovation consisted in attaching a triangular keel to
the under side of the envelope, with two gaps beneath which the cars
were suspended. Two Daimler Mercedes motors of 110 horse-power each were
placed one in each car, and the vessel carried sufficient fuel for a
60-hour cruise with the motors running at full speed. Each motor drove a
pair of three-bladed metal propellers rigidly attached to the framework
of the envelope and about 15 feet in diameter. There was a vertical
rudder at the stern of the envelope and horizontal controlling planes
were fixed on the sides of the envelope. The best performances and the
end of this dirigible were summarised as follows by Major Squier:--

'Its best performances were two long trips performed during the summer
of 1908. The first, on July 4th, lasted exactly 12 hours, during which
time it covered a distance of 235 miles, crossing the mountains
to Lucerne and Zurich, and returning to the balloon-house near
Friedrichshafen, on Lake Constance. The average speed on this trip
was 32 miles per hour. On August 4th, this airship attempted a 24-hour
flight, which was one of the requirements made for its acceptance by the
Government. It left Friedrichshafen in the morning with the intention
of following the Rhine as far as Mainz, and then returning to its
starting-point, straight across the country. A stop of 3 hours 30
minutes was made in the afternoon of the first day on the Rhine, to
repair the engine. On the return, a second stop was found necessary near
Stuttgart, due to difficulties with the motors, and some loss of gas.
While anchored to the ground, a storm arose which broke loose the
anchorage, and, as the balloon rose in the air, it exploded and took
fire (due to causes which have never been actually determined and
published) and fell to the ground, where it was completely destroyed. On
this journey, which