316 
POPULAE SCIENCE EEYIEW. 
felt and other material to prevent loss of heat by radiation. Connected 
•with the reservoir is a steam engine which actuates the axle of the driving 
wheels. Before starting the reservoir is charged with very highly heated 
water from a stationary steam boiler, the heat being such that a high steam 
pressure is generated in the reservoir. As this pressure is relieved by the 
exit of the steam into the engine, a portion of the water in the reservoir is 
converted into steam by the heat with which it is surcharged. This conver- 
sion continues until the lemperature of the water falls to 212°, and the 
machine can therefore be operated during the interval until nearly that 
point is reached. The experiments which were made consisted in charging 
the reservoir of the machine with hot water having a temperature of 360°, 
which yielded a steam pressure of 145 pounds per square inch, and then 
running the locomotive for a distance of six miles on the track of the 
Coney Island Railway. During the lirst half of the journey, which was 
accomplished in 15 minutes, the pressure fell to 00 pounds ; and at the 
expiration of the trip, which occupied 33 minutes, the gauge showed but 65 
pounds, the rate of diminution being much more rapid under high pressure 
than when the same had become lowered. The speed attained was twelve 
miles per hour, the burden being a single six ton car for 35 passengers ; we 
were assured, however, that the same time had been made with two carriages 
containing 70 persons. In actual use it is proposed to locate, at the termini 
or other points of the line, a sufficient number of stationary boilers from 
which the locomotive may be charged or its power renewed when exhausted. 
An Instrument for Measuring Fibres. — Herr J. Bohm communicates to 
the “ Industrie Blatter ” particulars of an instrument invented by him for 
measuring the diameters of fibres of wool, silk, and substances of a similar 
nature. The method of cutting across the fibre cannot be relied on, as it is 
almost impossible to make the cut perfectly vertical, and the slightest 
deviation towards obliquity will give an erroneous result. A better mode is 
to stretch the fibre to get rid of the kinks, and to turn it on its axis, as it 
were, under a microscope, so that the variations in its diameter may be 
distinctly observed, and measured with the micrometer ; its whole length 
also, should be passed under the object glass. For this purpose an ingenious 
little instrument has been constructed by Mr. Bohm. The inventor states 
that it not only has answered all the purposes for which he designed it, but 
has been useful in ways that he did not expect. It was found, for instance, 
that a hair ordinarily appeared to be unequally thick in various parts of its 
length ; this was owing to the long and short diameters of its oval section 
coming alternately under the vision, and the cause of the appearance was at 
once revealed by the instrument. And, again, the uniform decrease in the 
diameter of a hair towards its point, and the irregularity and inequality of 
fibres of wool from sick sheep, have been rendered visible. It has been 
found, too, that swellings and knots in otherwise straight fibres are produced 
by overstretching in the instrument, and the value of the arrangement for 
untwisting the fibres was here shown, for the knots began to uncurl the 
moment one end of the fibre was turned. A figure of this instrument is 
given in a recent number of the “ Scientific American.” 
The Resistance of the Hulls of Ships to Rolling Movements. — A memoir on 
this important subject has been presented to the French Academy by M. 
