Nephoscope
A nephoscope was an instrument for measuring the altitude, direction, and velocity of clouds in the 19th century. A ray of light of known velocity is emitted from a nephoscope, which strikes the base of a targeted cloud. The travel time of the return signal is used to estimate the distance to the cloud.
Description
A nephoscope was an instrument used to measuring the altitude, direction, and velocity of clouds in the 19th century. This is different from a "nephometer" which is an instrument used in measuring the amount of cloudiness.A ray of light of known velocity is emitted from a nephoscope, which strikes the base of a targeted cloud. The travel time of the return signal is used to estimate the distance to the cloud.
The distance to the cloud is calculated using the equation:
Mirror nephoscope
The following is from Scientific American and is in the public domain as it was written before 1923.Developed by Carl Gottfrid Fineman this instrument consists of a magnetic compass, the case of which is covered with a black mirror, around which is movable a circular metal frame. A
little window in this mirror enables the observer to see
the tip of the compass needle underneath. On the
surface of the mirror are engraved three concentric
circles and four diameters; one of the latter passes
through the middle of the little window. The mirror
constitutes a compass card, its radii corresponding to
the cardinal points. On the movable frame surrounding.the mirror is fixed a vertical pointer graduated in
millimeters, which can be moved· up and down by
means of a rack and pinion. The whole apparatus is
mounted on a tripod stand provided with leveling screws. To make an observation, the mirror is adjusted to the horizontal with the leveling-screws, and
is oriented to the meridian by moving the whole apparatus until the compass needle is seen, through the
window, to lie in the north-south line of the mirror
. The observer stands in such a position as to
bring the image of any chosen part of a cloud at the
center of the mirror, lind the vertical pointer is also
adjusted by screwing it up or down and by rotating
it around the mirror until its tip is reflected in the center' of the mirror. As the image of the cloud moves
toward the circumference of the mirror the observer
moves his head so as to keep the tip of the pointer
and the cloud image in coincidence. The radius along
which the image moves gives the direction of the cloud's
movement, and the time required to pass from one
circle to the next its relative speed, which may be reduced to certain arbitrary units.
This instrument is, however, not very easy to use,
and gives only moderately accurate measurements.
Comb nephoscope
The following is mostly Scientific American and is in the public domain as it was written before 1923.Developed by Louis Besson director of the
Observatory of Montsouris in 1912 this apparatus consists of a horizontal bar
fitted with several equidistant spikes and mounted on
the upper end of a vertical pole which can be rotated
on its axis. When an observation is to be made the
observer places himself in such a position that the
central spike is projected on any chosen part of a
cloud. Then, without altering his position, he causes
the "comb" to turn by means of two cords in such a
manner that the cloud is seen to follow along the line
of spikes. A graduated circle, turning with the vertical
pole, gives the direction of the cloud's motion ; it is
read with the aid of a fixed pointer. Moreover, when
the apparatus is once oriented, the observer can determine the relative speed of the cloud by noting the time
the latter requires to pass from one spike to the next.
If the instrument stands on level ground, so that the
observer's eye is always at the same height, and if the
interval between two successive spikes is equal to
one tenth of their altitude above the eye-level of the
observer, one need only multiply by 10 the time required
for the cloud to pass over one interval to determine
the time the cloud travels a horizontal distance equal
t.o its altitude.
M. Besson revived an old method of Bravais
for measuring the actual height of clouds. The apparatus in this case consists of a plate of glass having
parallel faces, mounted on a graduated vertical circle
which indicates its angle of inclination. A sheet of
water, situated at a lower level, serves as a
mirror to reflect the cloud. The water is contained in
a rel;!ervoir of blackened cement surrounded by shrubbery, and is only a small fraction of an inch in depth,
so that the wind may not disturb its level surface.
The observer, having mounted' the glass plate on the
horizontal axis of a. theodolite set on a window-sill some 30 or 40 feet above the ground, places
his eye close to it and adjusts its inclination so that
the images of a cloud reflected in the plate and in
the sheet of water coincide. Then from a curve traced
once for all on a sheet of plotting paper he reads off
the altitude of the cloud corresponding to the observed
angle on the glass plate. The curve is plotted from
simple trigonometrical calculations.
At the Observatory of Montsouris the degree of
cloudiness, i. e., the amount of the whole · sky covered
with clouds at a given moment, is determined by means
of the nephometer, also devised by M. Besson. This consists of a convex glass mirror, a segment
of a sphere, about twelve inches in diameter, in which is seen the reflection of the celestial vault divided into
ten sections of equal area by means of lines engraved
on the. glass. As shown in our front page engraving,
the meteorologist observes through an eyepiece fixed
in. an invariable position with respect to the mirror,
which latter turns freely on a vertical axis. The observer, whose own image partly obstructs sections 8, 9. and 10, notes the degree of cloudiness in the sections
numbered 1 to 7. The cloudiness of each section is estimated on a scale of 0 to 10 ; zero meaning no clouds and 10 entirely overcast. He now rotates the mirror and eyepiece 180 degrees and observes the cloudiness in sections 7, 5, and 2, which represent the
regions of the sky that at the first observation corresponded to sections 8, 9, and 10.