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1868. | Physics. 115 
about 0°4 inch internal diameter, but cylinders of 4 inches diameter ; 
these were connected at the bottom by a small tube. Thus the 
power, exerted by the pressure communicated through the connecting 
tubes, operating on the extended surface of the liquid in the cylin- 
ders, was increased a hundred-fold over that operating in the 
smaller U-Tube; but the friction could only have been increased 
ten-fold, giving therefore a ten-fold increase of delicacy. In order 
to observe accurately the rise and fall of the liquid in the cylinders, 
floats were introduced, on each of which was engraved a very fine 
horizontal line; and to measure accurately the comparative elevation 
or depression of these two lines, a finely divided scale and vernier 
were added, working with a delicate screw adjustment. With this 
it is possible to measure an elevation or depression of rsoth inch, 
which is sufficiently accurate for the purpose in view. 
On trying now to apply the instrument so constructed, and 
attempting to measure very minute variations of pressure, failure 
still seemed imminent; for although the motion of the water in 
the increased limbs of the U-tube could be measured to zessth inch, 
the water refused to move except under pressures exceeding that 
which would be indicated by so small a column: in other words, 
the water seemed to stick in the cylinders. After substituting ether 
for water the action of the manometer was quite satisfactory ; the 
lines on the floats always returned exactly to their original position 
after any disturbance, and its indications could be relied on to 
reooth inch. 
By the aid of this ether manometer the speed of any current of 
air in flues or chimneys can be measured by simply boring a hole 
one inch in diameter through the brickwork, and inserting two 
tubes, one with a bent, the other with a plain end as Brea 
described, and making the nécessary observation of the floats; and 
in this operation neither soot, heat, nor corrosive vapours can prove 
any hindrance. 
So sensitive is the apparatus, that on a windy day the effect of 
each successive gust of wind is observable, as it causes variations in 
the draught of the chimney. The instrument may be used as a 
wind gauge, by fixing through the roof of an observatory a small 
vertical pipe presenting a plain open end to the wind. The lower 
end of this pipe brought down into the observatory and connected 
with the ether manometer, would communicate the varying pressures 
due to the varying speed of the wind. 
Execrriciry.—M. Rondel has examined a phenomenon which 
has been noticed more than once by workers with induction coils. 
Tf while the current of a pile passes through the primary wire of 
a coil, one of the extremities of the secondary wire is brought near 
one of the extremities of the iron core, sparks can be drawn of 
EZ 
