Scientific American Supplement No. 360, November 25, 1882
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Various >> Scientific American Supplement No. 360, November 25, 1882
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IMPROVED GRAPE BAGS.
It stands to reason that were our summers warmer we should be able to
grow grapes successfully on open walls; it is therefore probable that
a new grape bag, the invention of M. Pelletier, 20 Rue de la Banque,
Paris, intended to serve a double purpose, viz., protecting the fruit
and hastening its maturity, will, when it becomes known, be welcomed in
this country. It consists of a square of curved glass so fixed to
the bag that the sun's rays are concentrated upon the fruit, thereby
rendering its ripening more certain in addition to improving its quality
generally. The glass is affixed to the bag by means of a light iron wire
support. It covers that portion of it next the sun, so that it increases
the amount of light and warms the grapes without scorching them, a
result due to the convexity of the glass and the layer of air between it
and the bag. M. Pelletier had the idea of rendering these bags cheaper
by employing plain squares instead of curved ones, but the advantage
thus obtained was more than counterbalanced by their comparative
inefficacy. In practice it was found that the curved squares gave an
average of 7 deg. more than the straight ones, while there was a difference
of 10 deg. when the bags alone were used, thus plainly demonstrating the
practical value of the invention.
Whether these glass-fronted bags would have much value in the case of
grapes grown under glass in the ordinary way is a question that can only
be determined by actual experiment; but where the vines are on walls,
either under glass screens or in the open air, so that the bunches feel
the full force of the sun's rays, there can be no doubt as to their
utility, and it is probable that by their aid many of the continental
varieties which we do not now attempt to grow in the open, and which are
scarcely worthy of a place under glass, might be well ripened. At
any rate we ought to give anything a fair trial which may serve to
neutralize, if only in a slight degree, the uncertainty of our summers.
As it is, we have only about two varieties of grapes, and these not the
best of the hardy kinds, as regards flavor and appearance, that ripen
out of doors, and even these do not always succeed. We know next to
nothing of the many really well-flavored kinds which are so much
appreciated in many parts of the Continent. The fact is, our outdoor
culture of grapes offers a striking contrast to that practiced under
glass, and although our comparatively sunless and moist climate affords
some excuse for our shortcomings in this respect, there is no valid
reason for the utter want of good culture which is to be observed in a
general way.
[Illustration: GRAPE BAG.--OPEN.]
Given intelligent training, constant care in stopping the laterals, and
checking mildew as well as thinning the berries, allowing each bunch to
get the full benefit of sun and air, and I believe good eatable grapes
would often be obtained even in summers marked by a low average
temperature.
[Illustration: GRAPE BAG.--CLOSED.]
If, moreover, to a good system of culture we add some such mechanical
contrivance as that under notice whereby the bunches enjoy an average
warmth some 10 deg. higher than they otherwise would do, we not only insure
the grapes coming to perfection in favored districts, but outdoor
culture might probably be practiced in higher latitudes than is now
practicable.
[Illustration: CURVED GLASS FOR FRONT OF BAG.]
The improved grape bag would also offer great facilities for destroying
mildew or guarantee the grapes against its attacks, as a light dusting
administered as soon as the berries were fairly formed would suffice for
the season, as owing to the glass protecting the berries from driving
rains, which often accompany south or south-west winds in summer and
autumn, the sulphur would not be washed off.
[Illustration: CURVED GLASS FIXED ON BAG.]
The inventor claims, and we should say with just reason, that these
glass fronted bags would be found equally serviceable for the ripening
of pears and other choice fruits, and with a view to their being
employed for such a purpose, he has had them made of varying sizes and
shapes. In conclusion, it may be observed that, in addition to advancing
the maturity of the fruits to which they are applied, they also serve to
preserve them from falling to the ground when ripe.--J. COBNHILL, _in
the Garden_.
* * * * *
UTILIZATION OF SOLAR HEAT.
At a popular fete in the Tuileries Gardens I was struck with an
experiment which seems deserving of the immediate attention of the
English public and military authorities.
Among the attractions of the fete was an apparatus for the concentration
and utilization of solar heat, and, though the sun was not very
brilliant, I saw this apparatus set in motion a printing machine which
printed several thousand copies of a specimen newspaper entitled the
_Soleil Journal_.
The sun's rays are concentrated in a reflector, which moves at the
same rate as the sun and heats a vertical boiler, setting the motive
steam-engine at work. As may be supposed, the only object was to
demonstrate the possibility of utilizing the concentrated heat of the
solar rays; but I closely examined it, because the apparatus seems
capable of great utility in existing circumstances. Here in France,
indeed, there is a radical drawback--the sun is often overclouded.
Thousands of years ago the idea of utilizing the solar rays must have
suggested itself, and there are still savage tribes who know no other
mode of combustion; but the scientific application has hitherto been
lacking. This void this apparatus will fill up. About fifteen years ago
Professor Mouchon, of Tours, began constructing such an apparatus, and
his experiments have been continued by M. Pifre, who has devoted much
labor and expense to realizing M. Mouchou's idea. A company has now come
to his aid, and has constructed a number of apparatus of different sizes
at a factory which might speedily turn out a large number of them. It is
evident that in a country of uninterrupted sunshine the boiler might be
heated in thirty or forty minutes. A portable apparatus could boil two
and one-half quarts an hour, or, say, four gallons a day, thus supplying
by distillation or ebullition six or eight men. The apparatus can be
easily carried on a man's back, and on condition of water, even of the
worst quality, being obtainable, good drinking and cooking water is
insured. M. De Rougaumond, a young scientific writer, has just published
an interesting volume on the invention. I was able yesterday to verify
his statements, for I saw cider made, a pump set in motion, and coffee
made--in short, the calorific action of the sun superseding that of
fuel. The apparatus, no doubt, has not yet reached perfection, but as it
is it would enable the soldier in India or Egypt to procure in the field
good water and to cook his food rapidly. The invention is of especial
importance to England just now, but even when the Egyptian question is
settled the Indian troops might find it of inestimable value.
Red tape should for once be disregarded, and a competent commission
forthwith sent to 30 Rue d'Assas, with instructions to report
immediately, for every minute saved may avoid suffering for Englishmen
fighting abroad for their country. I may, of course, be mistaken, but
a commission would decide, and if the apparatus is good the slightest
delay in its adoption would be deplorable.--_Paris Correspondence London
Times_.
* * * * *
HOW TO ESTABLISH A TRUE MERIDIAN.
[Footnote: A paper read before the Engineers' Club of Philadelphia.]
By PROFESSOR L. M. HAUPT.
INTRODUCTORY.
The discovery of the magnetic needle was a boon to mankind, and has been
of inestimable service in guiding the mariner through trackless waters,
and the explorer over desert wastes. In these, its legitimate uses, the
needle has not a rival, but all efforts to apply it to the accurate
determination of permanent boundary lines have proven very
unsatisfactory, and have given rise to much litigation, acerbity, and
even death.
For these and other cogent reasons, strenuous efforts are being made to
dispense, so far as practicable, with the use of the magnetic needle
in surveying, and to substitute therefor the more accurate method of
traversing from a true meridian. This method, however, involves a
greater degree of preparation and higher qualifications than are
generally possessed, and unless the matter can be so simplified as to be
readily understood, it is unreasonable to expect its general application
in practice.
Much has been written upon the various methods of determining, the
true meridian, but it is so intimately related to the determination of
latitude and time, and these latter in turn upon the fixing of a true
meridian, that the novice can find neither beginning nor end. When to
these difficulties are added the corrections for parallax, refraction,
instrumental errors, personal equation, and the determination of the
probable error, he is hopelessly confused, and when he learns that time
may be sidereal, mean solar, local, Greenwich, or Washington, and he is
referred to an ephemeris and table of logarithms for data, he becomes
lost in "confusion worse confounded," and gives up in despair, settling
down to the conviction that the simple method of compass surveying is
the best after all, even if not the most accurate.
Having received numerous requests for information upon the subject, I
have thought it expedient to endeavor to prepare a description of the
method of determining the true meridian which should be sufficiently
clear and practical to be generally understood by those desiring to make
use of such information.
This will involve an elementary treatment of the subject, beginning with
the
DEFINITIONS.
The _celestial sphere_ is that imaginary surface upon which all
celestial objects are projected. Its radius is infinite.
The _earth's axis_ is the imaginary line about which it revolves.
The _poles_ are the points in which the axis pierces the surface of the
earth, or of the celestial sphere.
A _meridian_ is a great circle of the earth cut out by a plane passing
through the axis. All meridians are therefore north and south lines
passing through the poles.
From these definitions it follows that if there were a star exactly at
the pole it would only be necessary to set up an instrument and take a
bearing to it for the meridian. Such not being the case, however, we are
obliged to take some one of the near circumpolar stars as our object,
and correct the observation according to its angular distance from the
meridian at the time of observation.
For convenience, the bright star known as Ursae Minoris or Polaris, is
generally selected. This star apparently revolves about the north pole,
in an orbit whose mean radius is 1 deg. 19' 13",[1] making the revolution in
23 hours 56 minutes.
[Footnote 1: This is the codeclination as given in the Nautical Almanac.
The mean value decreases by about 20 seconds each year.]
During this time it must therefore cross the meridian twice, once above
the pole and once below; the former is called the _upper_, and the
latter the _lower meridian transit or culmination_. It must also pass
through the points farthest east and west from the meridian. The former
is called the _eastern elongation_, the latter the _western_.
An observation may he made upon Polaris at any of these four points,
or at any other point of its orbit, but this latter case becomes too
complicated for ordinary practice, and is therefore not considered.
If the observation were made upon the star at the time of its upper or
lower culmination, it would give the true meridian at once, but this
involves a knowledge of the true local time of transit, or the longitude
of the place of observation, which is generally an unknown quantity; and
moreover, as the star is then moving east or west, or at right angles to
the place of the meridian, at the rate of 15 deg. of arc in about one hour,
an error of so slight a quantity as only four seconds of time would
introduce an error of one minute of arc. If the observation be made,
however, upon either elongation, when the star is moving up or down,
that is, in the direction of the vertical wire of the instrument, the
error of observation in the angle between it and the pole will be
inappreciable. This is, therefore, the best position upon which to make
the observation, as the precise time of the elongation need not be
given. It can be determined with sufficient accuracy by a glance at the
relative positions of the star Alioth, in the handle of the Dipper,
and Polaris (see Fig. 1). When the line joining these two stars is
horizontal or nearly so, and Alioth is to the _west_ of Polaris, the
latter is at its _eastern_ elongation, and _vice versa_, thus:
[Illustration]
But since the star at either elongation is off the meridian, it will
be necessary to determine the angle at the place of observation to be
turned off on the instrument to bring it into the meridian. This angle,
called the azimuth of the pole star, varies with the latitude of the
observer, as will appear from Fig 2, and hence its value must be
computed for different latitudes, and the surveyor must know his
_latitude_ before he can apply it. Let N be the north pole of the
celestial sphere; S, the position of Polaris at its eastern elongation;
then N S=1 deg. 19' 13", a constant quantity. The azimuth of Polaris at the
latitude 40 deg. north is represented by the angle N O S, and that at 60 deg.
north, by the angle N O' S, which is greater, being an exterior angle
of the triangle, O S O. From this we see that the azimuth varies at the
latitude.
We have first, then, to _find the latitude of the place of observation_.
Of the several methods for doing this, we shall select the simplest,
preceding it by a few definitions.
A _normal_ line is the one joining the point directly overhead, called
the _zenith_, with the one under foot called the _nadir_.
The _celestial horizon_ is the intersection of the celestial sphere by a
plane passing through the center of the earth and perpendicular to the
normal.
A _vertical circle_ is one whose plane is perpendicular to the horizon,
hence all such circles must pass through the normal and have the zenith
and nadir points for their poles. The _altitude_ of a celestial object
is its distance above the horizon measured on the arc of a vertical
circle. As the distance from the horizon to the zenith is 90 deg., the
difference, or _complement_ of the altitude, is called the _zenith
distance_, or _co-altitude_.
The _azimuth_ of an object is the angle between the vertical plane
through the object and the plane of the meridian, measured on the
horizon, and usually read from the south point, as 0 deg., through west, at
90, north 180 deg., etc., closing on south at 0 deg. or 360 deg..
These two co-ordinates, the altitude and azimuth, will determine the
position of any object with reference to the observer's place. The
latter's position is usually given by his latitude and longitude
referred to the equator and some standard meridian as co-ordinates.
The _latitude_ being the angular distance north or south of the equator,
and the _longitude_ east or west of the assumed meridian.
We are now prepared to prove that _the altitude of the pole is equal to
the latitude of the place of observation_.
Let H P Z Q, etc., Fig. 2, represent a meridian section of the sphere,
in which P is the north pole and Z the place of observation, then H H
will be the horizon, Q Q the equator, H P will be the altitude of P,
and Q Z the latitude of Z. These two arcs are equal, for H C Z = P C
Q = 90 deg., and if from these equal quadrants the common angle P C Z be
subtracted, the remainders H C P and Z C Q, will be equal.
To _determine the altitude of the pole_, or, in other words, _the
latitude of the place_.
Observe the altitude of the pole star _when on the meridian_, either
above or below the pole, and from this observed altitude corrected for
refraction, subtract the distance of the star from the pole, or its
_polar distance_, if it was an upper transit, or add it if a lower.
The result will be the required latitude with sufficient accuracy for
ordinary purposes.
The time of the star's being on the meridian can be determined with
sufficient accuracy by a mere inspection of the heavens. The refraction
is _always negative_, and may be taken from the table appended by
looking up the amount set opposite the observed altitude. Thus, if the
observer's altitude should be 40 deg. 39' the nearest refraction 01' 07",
should be subtracted from 40 deg. 37' 00", leaving 40 deg. 37' 53" for the
latitude.
TO FIND THE AZIMUTH OF POLARIS.
As we have shown the azimuth of Polaris to be a function of the
latitude, and as the latitude is now known, we may proceed to find the
required azimuth. For this purpose we have a right-angled spherical
triangle, Z S P, Fig. 4, in which Z is the place of observation, P the
north pole, and S is Polaris. In this triangle we have given the polar
distance, P S = 10 deg. 19' 13"; the angle at S = 90 deg.; and the distance Z
P, being the complement of the latitude as found above, or 90 deg.--L.
Substituting these in the formula for the azimuth, we will have sin. Z =
sin. P S / sin P Z or sin. of Polar distance / sin. of co-latitude, from
which, by assuming different values for the co-latitude, we compute the
following table:
AZIMUTH TABLE FOR POINTS BETWEEN 26 deg. and 50 deg. N. LAT.
LATTITUDES
___________________________________________________________________
| | | | | | | |
| Year | 26 deg. | 28 deg. | 30 deg. | 32 deg. | 34 deg. | 36 deg. |
|______|_________|__________|_________|_________|_________|_________|
| | | | | | | |
| | deg. ' " | deg. ' " | deg. ' " | deg. ' " | deg. ' " | deg. ' " |
| 1882 | 1 28 05 | 1 29 40 | 1 31 25 | 1 33 22 | 1 35 30 | 1 37 52 |
| 1883 | 1 27 45 | 1 29 20 | 1 31 04 | 1 33 00 | 1 35 08 | 1 37 30 |
| 1884 | 1 27 23 | 1 28 57 | 1 30 41 | 1 32 37 | 1 34 45 | 1 37 05 |
| 1885 | 1 27 01 | 1 28 351/2 | 1 30 19 | 1 32 14 | 1 34 22 | 1 36 41 |
| 1886 | 1 26 39 | 1 28 13 | 1 29 56 | 1 31 51 | 1 33 57 | 1 36 17 |
|______|_________|__________|_________|_________|_________|_________|
| | | | | | | |
| Year | 38 deg. | 40 deg. | 42 deg. | 44 deg. | 46 deg. | 48 deg. |
|______|_________|__________|_________|_________|_________|_________|
| | | | | | | |
| | deg. ' " | deg. ' " | deg. ' " | deg. ' " | deg. ' " | deg. ' " |
| 1882 | 1 40 29 | 1 43 21 | 1 46 33 | 1 50 05 | 1 53 59 | 1 58 20 |
| 1883 | 1 40 07 | 1 42 58 | 1 46 08 | 1 49 39 | 1 53 34 | 1 57 53 |
| 1884 | 1 39 40 | 1 42 31 | 1 45 41 | 1 49 11 | 1 53 05 | 1 57 23 |
| 1885 | 1 39 16 | 1 42 07 | 1 45 16 | 1 48 45 | 1 52 37 | 1 56 54 |
| 1886 | 1 38 51 | 1 41 41 | 1 44 49 | 1 48 17 | 1 52 09 | 1 56 24 |
|______|_________|__________|_________|_________|_________|_________|
| | |
| Year | 50 deg. |
|______|_________|
| | |
| | deg. ' " |
| 1882 | 2 03 11 |
| 1883 | 2 02 42 |
| 1884 | 2 02 11 |
| 1885 | 2 01 42 |
| 1886 | 2 01 11 |
|______|_________|
An analysis of this table shows that the azimuth this year (1882)
increases with the latitude from 1 deg. 28' 05" at 26 deg. north, to 2 deg. 3' 11"
at 50 deg. north, or 35' 06". It also shows that the azimuth of Polaris at
any one point of observation decreases slightly from year to year. This
is due to the increase in declination, or decrease in the star's polar
distance. At 26 deg. north latitude, this annual decrease in the azimuth
is about 22", while at 50 deg. north, it is about 30". As the variation in
azimuth for each degree of latitude is small, the table is only computed
for the even numbered degrees; the intermediate values being readily
obtained by interpolation. We see also that an error of a few minutes of
latitude will not affect the result in finding the meridian, e.g., the
azimuth at 40 deg. north latitude is 1 deg. 43' 21", that at 41 deg. would be 1 deg. 44'
56", the difference (01' 35") being the correction for one degree of
latitude between 40 deg. and 41 deg.. Or, in other words, an error of one degree
in finding one's latitude would only introduce an error in the azimuth
of one and a half minutes. With ordinary care the probable error of the
latitude as determined from the method already described need not exceed
a few minutes, making the error in azimuth as laid off on the arc of an
ordinary transit graduated to single minutes, practically zero.
REFRACTION TABLE FOR ANY ALTITUDE WITHIN THE LATITUDE OF THE UNITED
STATES.
_____________________________________________________
| | | | |
| Apparent | Refraction | Apparent | Refraction |
| Altitude. | _minus_. | Altitude. | _minus_. |
|___________|______________|___________|______________|
| | | | |
| 25 deg. | 0 deg. 2' 4.2" | 38 deg. | 0 deg. 1' 14.4" |
| 26 | 1 58.8 | 39 | 1 11.8 |
| 27 | 1 53.8 | 40 | 1 9.3 |
| 28 | 1 49.1 | 41 | 1 6.9 |
| 29 | 1 44.7 | 42 | 1 4.6 |
| 30 | 1 40.5 | 43 | 1 2.4 |
| 31 | 1 36.6 | 44 | 0 0.3 |
| 32 | 1 33.0 | 45 | 0 58.1 |
| 33 | 1 29.5 | 46 | 0 56.1 |
| 34 | 1 26.1 | 47 | 0 54.2 |
| 35 | 1 23.0 | 48 | 0 52.3 |
| 36 | 1 20.0 | 49 | 0 50.5 |
| 37 | 1 17.1 | 50 | 0 48.8 |
|___________|______________|___________|______________|
APPLICATIONS.
In practice to find the true meridian, two observations must be made at
intervals of six hours, or they may be made upon different nights. The
first is for latitude, the second for azimuth at elongation.
To make either, the surveyor should provide himself with a good transit
with vertical arc, a bull's eye, or hand lantern, plumb bobs, stakes,
etc.[1] Having "set up" over the point through which it is proposed to
establish the meridian, at a time when the line joining Polaris and
Alioth is nearly vertical, level the telescope by means of the attached
level, which should be in adjustment, set the vernier of the vertical
arc at zero, and take the reading. If the pole star is about making its
_upper_ transit, it will rise gradually until reaching the meridian as
it moves westward, and then as gradually descend. When near the highest
part of its orbit point the telescope at the star, having an assistant
to hold the "bull's eye" so as to reflect enough light down the tube
from the object end to illumine the cross wires but not to obscure the
star, or better, use a perforated silvered reflector, clamp the tube in
this position, and as the star continues to rise keep the _horizontal_
wire upon it by means of the tangent screw until it "rides" along this
wire and finally begins to fall below it. Take the reading of the
vertical arc and the result will be the observed altitude.
[Footnote 1: A sextant and artificial horizon may be used to find the
_altitude_ of a star. In this case the observed angle must be divided by
2.]
ANOTHER METHOD.
It is a little more accurate to find the altitude by taking the
complement of the observed zenith distance, if the vertical arc has
sufficient range. This is done by pointing first to Polaris when at
its highest (or lowest) point, reading the vertical arc, turning the
horizontal limb half way around, and the telescope over to get another
reading on the star, when the difference of the two readings will be the
_double_ zenith distance, and _half_ of this subtracted from 90 deg. will be
the required altitude. The less the time intervening between these two
pointings, the more accurate the result will be.
Having now found the altitude, correct it for refraction by subtracting
from it the amount opposite the observed altitude, as given in the
refraction table, and the result will be the latitude. The observer must
now wait about six hours until the star is at its western elongation,
or may postpone further operations for some subsequent night. In the
meantime he will take from the azimuth table the amount given for his
date and latitude, now determined, and if his observation is to be made
on the western elongation, he may turn it off on his instrument, so
that when moved to zero, _after_ the observation, the telescope will be
brought into the meridian or turned to the right, and a stake set by
means of a lantern or plummet lamp.
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