MEASUREMENT--_Continued_
Weight, Time, Heat, Light, Electricity measured with new precision
. . . Exact measurement means interchangeable designs, and points
the way to utmost economies . . . The Bureau of Standards at
Washington . . . Measurement in expert planning and reform.
[Illustration: Ancient Egyptian balance.]
The Balance in Measurement.
Our grandfathers supposed that trade began in barter; we have been able
to go one step further back in history to find that barter followed upon
the custom of exchanging presents. This custom, among shrewd and
self-respecting people, came at length to a degree of fairness, and led
to rough and ready modes of weighing, gradually improved. In the British
Museum, in a papyrus of Hunnafer, who lived in Egypt thirty-three
centuries ago, we have pictured a well-constructed balance of equal
arms, in which a feather is outweighing a human soul. In its successive
improvements the balance registers the progress of many arts and
sciences, and in its turn has promoted them all. It must be built of a
metal, or an alloy, hard, durable, and not easily corroded. Its centre
of motion should be a little above its centre of gravity; its knife edge
should have an angle of about 60 degrees. Appliances must render it easy
to lift the weighing apparatus when out of use, so that unnecessary wear
of the knife edge may be avoided, as well as needless strain throughout
the structure. Air currents should be kept off by a suitable case, or,
better still, the instrument should be enclosed in a receiver exhausted
of air altogether. The weights, made with scrupulous care of standard
metal or alloy, should be guarded from tampering, abrasion, and
corrosion, from dirt or other accretions. A weighing should be slowly
performed, the weights placed in the center of one pan, the object
weighed in the center of the other pan; to eliminate errors due to
inequality in the length of arms, the article weighed and the weights
are then made to exchange places. The platform should be of the utmost
strength and rigidity, so as precisely to maintain its level at all
times.
[Illustration: A Rueprecht balance.]
As long ago as 1798 a balance was erected having an accuracy of one part
in 1,600,000; fifty years later ten-fold greater accuracy had been
attained; to-day results much more astonishing are achieved. A precision
balance manufactured by Messrs. Albert Rueprecht & Son, Vienna, is shown
on page 220, as furnished in 1902 to the International Bureau of Weights
and Measures at Sevres, France. It is provided with means for applying
the smallest weights of platinum from a distance of three to four
metres, so as to guard against perturbations due to the warmth of an
operator’s body. The weights may be shifted from one pan to the other,
and the oscillations observed through a telescope, at a distance of four
metres. This balance will detect the 1/500 of a milligram when weighing
a mass of 500 grams, or one part in 250,000,000. Such balances, and
those of Paul Bunge, of Hamburg, require ten to twenty months of skilled
labor for their completion. The International Bureau of Weights and
Measures has a balance of extraordinary sensitiveness at the Pavillon de
Breteuil, Sevres, where the work of the Bureau goes forward. This
instrument measures the difference in the attraction of the earth for a
mass of one kilogram when that weight is moved nearer to or farther from
the centre of the earth by as little as one centimetre. Thus placing two
weights, of common shape, each a kilogram, one on top of the other, and
two other weights in the other pan beside one another, would introduce a
noteworthy difference in a comparison.
Measurement of Time.
At the very dawn of civilization, the day, however crudely, was divided
into parts. These parts, long afterward, probably in Babylonia, became
the twenty-four hours which have descended to us. The means of
time-keeping came first, in all likelihood, from measuring the simple
shadow of a stick, the gnomon, still set up as a sun-dial in our
gardens. Next came an hour-glass with its falling sand; the clepsydra,
with its water dropping from a jar; the burning of candles definite in
length. At last came the supreme discovery that a pendulum, of given
length, if kept in one place oscillates in an unvarying period, be its
arc of motion long or short. Tradition has it that in Arabia, about the
year 1000 A. D., the pendulum was used in time-keeping. Granting this to
be true, we must nevertheless give Galileo credit for his independent
discovery as he observed the swaying lamp of the cathedral at Pisa,
early in the seventeenth century. In 1657 Huygens employed a pendulum in
the construction of a clock which, of course, displayed a new approach
to accuracy. In 1792 Borda and Cassini had improved their time-pieces so
as to be correct within one part in 375,000, that is to one second in
104 hours. For the sake of portability, clocks were gradually reduced in
size until they became watches. Instead of a pendulum they were
furnished with its equivalent, a balance wheel, Pierre Le Roy having
discovered that there is in every spring a certain length where all the
vibrations, great or small, are performed in approximately the same
period. For actuation, watches were provided with mainsprings which have
steadily undergone improvement in quality and in placing.
Time-Pieces Improved.
Many refinements have brought the time-keeper for the ship, the
observatory, the railroad, to virtual perfection. Its wheels, pinions,
balance-staffs are manufactured automatically, as at Waltham,
Massachusetts, to an accuracy of 1/5000 inch or even less, thanks to
that great inventor, Mr. Duane H. Church. In modern watch-making the
most durable materials are used, magnetic perturbations are avoided by
employing alloys insensitive to magnetism, and the effects of
fluctuating temperatures are withstood by Earnshaw’s compensated balance
wheel. This wheel is in halves, each nearly semicircular and attached
at one end to a stout diameter. Its outer rim, being made of brass, when
warmed expands more than its inner rim of steel. Thus, in a rising
temperature the wheel curves inward with its duly placed weights, so
that the reduction in elasticity of the hair-spring caused by heat is
compensated. Experiments are afoot which look toward a marked
improvement in the making of time-pieces, by using invar, a nickel-steel
with practically no expansibility by heat. This alloy is already
employed for pendulums with satisfactory results, both at the Naval
Observatory and at the Bureau of Standards, in Washington. It has been
described on page 169.
[Illustration: Earnshaw compensated balance wheel for watches.]
The Best Clocks in the World.
At the Paris Observatory the standard clock, by Winnerl, is in a vault
twenty-seven metres underground. At that depth the temperature changes
are less than one fifth of a degree during the year, yet the effect of
barometric changes on the rate of the clock have proved to be serious.
This difficulty is avoided in the Naval Observatory at Washington, by
enclosing the standard clock in an air-tight case within which the air
is reduced to a pressure lower than that ever shown by a barometer at
that level. To avoid risks of air leaking through this case were it to
be pierced by a moving axle, this clock is actuated by weights lifted
electrically by a small primary battery. The slight electric current
required has no perturbing effect on the clock. This time-piece,
provided with an escapement of great excellence, was manufactured by
Clemens Riefler of Munich.
At the Observatory of the Case School of Applied Science, Cleveland,
Ohio, another Riefler clock has a mean error of but .015 second per day.
This means that in a year the total error is not more than 5.475
seconds, or one part in 5,760,000 of the 365 days. Such errors, minute
as they are, give a good deal of trouble when they are irregular, that
is, when the clock is sometimes slow, sometimes fast, in a fashion
apparently lawless. When the divergences are fairly constant they can
usually be traced to their source, making it feasible to apply a remedy.
[Illustration: Riefler clock.]
Ascertaining the Force of Gravity.
A pendulum which swings once in a second at the base of a tall tower
will require for the same travel a little more than a second when borne
to the top of the tower, because then further from the centre of the
earth. Still greater will be the difference in its periods as it swings
first at the base of a mountain and next at its summit. A pendulum,
therefore, is a means of learning the force of gravity at a given place,
and without sacrifice of accuracy it is well that it should be as small
as possible. In 1890, Professor T. C. Mendenhall, then superintendent of
the United States Coast and Geodetic Survey, designed a pendulum one
fourth the length of those previously used, and of admirable precision.
Afterward pendulums were built of dimensions further reduced to about
two and one half inches in length, with periods of oscillation of one
fourth of a second. Such pendulums are easily carried to stations
difficult of access, and have been employed on the summits of high
mountains, including Pike’s Peak: their indications agree well with
those of the larger and somewhat cumbersome apparatus previously used.
Heat Measured.
Much the most convenient means of measuring temperature is the common
glass tube filled with mercury. This metal is chosen because a liquid,
and because it varies extremely in bulk when warmed or cooled. Materials
of parallel susceptibility are adopted for instruments which measure the
intensity of magnetism or of electricity, the working core of the
instrument being made of a substance highly responsive to magnetism or
to electricity.
A mercurial thermometer, for all its convenience, has its accuracy
assailed on more sides than one. When the barometric pressure rises, the
bulb is compressed; when the barometer falls, the bulb enlarges by
virtue of the diminution in atmospheric pressure. Further, when its
graduated tube is upright the mercury exerts a distending pressure which
introduces error. At all temperatures the metal is giving off a vapor
which has tension, in its upper ranges entailing marked inaccuracies.
The glass itself of which the instrument is made, when of ordinary
composition, spontaneously undergoes changes of volume. While this is a
minor source of error it may be almost completely avoided by using a
boro-silicate glass from the factory of Schott & Genossen, at Jena.
Other substances than mercury are employed in thermometers with
gratifying results. Hydrogen gas is found very suitable within the
interval from -30° to 200° Centigrade. Pentane serves in temperatures
reaching down to -180°.
But it is in alliances with electricity that the measurement of heat has
its broadest scope and utmost exactitude. It was long ago remarked that
heating a metallic conductor increases its resistance to the flow of an
electric current; to measure that resistance in a platinum wire serves,
therefore, to measure its temperature. An instrument on this principle
is the bolometer of the late Professor S. P. Langley, of Washington.
Through a strip of platinum barely 1/500 inch in width, and less than
1/5000 inch in thickness, a current of electricity flows continuously.
When radiation, visible or invisible, on occasion from a star, falls
upon it, the strip when warmed by as little as one millionth of a
degree duly records the fact. An instrument, modified from the Crookes
radiometer by Professor E. F. Nichols of Columbia University, New York,
is more sensitive still. An exhausted hollow metal block has a window of
fluorite, a mineral transparent to ether vibrations of a long range of
frequencies. Suspended inside the block is a fine quartz fibre
supporting a horizontal bar, at the ends of which are attached thin
plates of mica, blackened on one side. Rays passing through the fluorite
window strike the blackened side of the mica, which is parallel and
opposite to it. The resulting rise in temperature causes the vane to
revolve against the torsion of the quartz fibre. The angle of torsion
when thermal equilibrium is reached, measures the intensity of the
incident radiation.
Another principle is adopted in the electrical instruments which expose
to heat a junction of two different materials, usually metallic, giving
rise to an electric current, easily measured. Experience shows that the
most satisfactory couples for temperatures between 300° C. (570° F.) and
1600° C. (2900° F.) are those devised by M. Le Chatelier, one half
consisting of pure platinum, the other half an alloy of ten per cent.
rhodium and ninety per cent. platinum. Such instruments are
indispensable in the arts which employ high temperatures. In producing
chlorine by the Deacon process, or in the baking of porcelain, an undue
variation of temperature of only twenty degrees may cause a complete
failure of the operation.
The Measurement of Light.
It is probable that about one half the electricity from the dynamos of
America is sent into lamps, and this is but part of the whole outlay for
light, still chiefly produced by petroleum and gas. Hence the importance
of measuring the light from lamps, jets, and mantles of various kinds,
and testing the efficiency of shades and reflectors. First of all comes
the decision as to a standard for comparison. Great Britain has adopted
the Harcourt lamp, consuming pentane, as a standard for ten
candle-power, referring to the old time candle of spermaceti. Germany
employs the amylacetate lamp introduced by Von Hefner Alteneck, as a
standard for its Hefner unit of illumination. Both lamps share in a
difficulty which attends all combustion: atmospheric conditions which
vary from hour to hour, from place to place, greatly affect the
intensity of a flame. Hence incandescent lamps, which have been compared
with these fundamental standards, are used as working standards. They
can be operated by a uniform current of specified voltage, and after a
hundred hours’ use their constancy of radiation for a considerable
period is remarkable.
[Illustration: Photometer. A, standard candle. B, gas flame. S, sliding
frame.]
Having settled upon a standard candle or lamp the measurement of light
demands extreme care, and, at the best, can never approach the accuracy
of other laboratory measurements. Many photometers have been invented,
some of them highly elaborate, but the type oftenest used remains in
essence the simple instrument long ago devised by Bunsen. On a frame
supported by a stand, S, is stretched a sheet of white paper in the
centre of which is a grease spot. This spot allows more light to pass
through it and consequently reflects less than the unmarked portion of
the paper. If the sheet is more strongly lighted from behind than from
in front, it appears bright on a dark ground. If it is illuminated more
strongly in front than at the back it will seem dark upon a bright
ground. When equal lights fall on both sides, the spot becomes
invisible, since it can then appear neither darker nor brighter than the
surrounding paper. In its simplest use the screen is placed between a
standard candle or lamp at A and the light to be measured at B: the
screen is moved along its graduated slide until the grease spot
vanishes. If the screen is twice as far from B as from A when the spot
disappears, then B is four times as intense as A in light; if the screen
were thrice as far from B as from A, then B would be nine-fold as bright
as A, the intensity of light diminishing as the square of the distance
of its source.
An open-arc lamp, without a reflector, sends to the ground a fairly wide
ring of brilliant rays; on both sides of that ring the illumination is
feeble. Other sources of light also vary a good deal in the brilliancy
of the beams which they emit in various planes. It is therefore usual to
measure the light from a lamp as sent forth in all planes, or at least
in its principal planes. When incandescent lamps are brought to a
photometer they are as a rule placed on a spindle turning so swiftly
that their mean horizontal candle-power may be read at once. For
measuring the mean spherical intensity a photometer devised by Professor
Matthews of Purdue University is employed. This apparatus has a series
of mirrors arranged in a semicircle around a lamp, reflecting all the
received light upon a single surface.
Light may have great brilliancy and yet be undesirable from its color;
we are all familiar with the havoc that gas light may play with hues of
blossom and leaf that in sunshine are beautiful. Through ages untold the
human eye has been seeing by rays from the sun, and from immemorial
habit is best served by light of similar quality. A simple instrument,
the spectrometer, casts upon a screen the spectrum from a mercury tube,
a Nernst lamp, a Welsbach mantle, or other illuminant, and enables us to
compare it with the spectrum of sunshine. Then, as in placing a light
pink shade over a Welsbach mantle, we act on the intimations of analysis
greatly to the relief of the eye.
An incandescent bulb or mantle may be satisfactory both in brilliancy
and color, but a further question is, How long will the filament or the
mantle last, and at what point in deterioration should it be discarded?
Tests during the first, the fiftieth, the hundredth, and other
successive hours will tell us how much the intensity falls off. Just
when a bulb or a mantle should be dismissed from service depends partly
on the rate of deterioration, and partly on the prices of bulbs and
current, of mantles and gas.
Hardly less important than testing sources of light is the
investigation of their reflectors and shades. As a rule our lamps are
too brilliant, and in many cases they send their light in wasteful
directions. It is a general and absurd practice to buy a dollar’s worth
of light and then kill sixty cents’ worth of it with a thick opal or
cut-glass shade. Examination with the photometer has revealed that many
popular patterns of reflectors and shades are most ineffective, while
those of the Holophane make, when kept scrupulously clean, send the
light just where it does most good and at the lowest possible
expenditure of energy. This theme has attention on page 78.[28]
[28] A capital treatise on the subject of lighting, and the
measurement of light, is Louis Bell’s “Art of Illumination.” New
York, McGraw Publishing Co., 1902. $2.50. Its author (August, 1906)
is preparing a new and revised edition.
The Sky as a Field for Measurement.
The sky has been the supreme field for measurements more refined from
age to age. Professor William Stanley Jevons, in “Principles of
Science,” says: “At Greenwich Observatory in the present day, the
hundredth part of a second is not thought an inconsiderable portion of
time. The ancient Chaldeans recorded an eclipse to the nearest hour, and
even the early Alexandrian astronomers thought it superfluous to
distinguish between the edge and centre of the sun. By the introduction
of the astrolabe, Ptolemy and the later Alexandrian astronomers could
determine the places of the heavenly bodies within about ten minutes of
arc. But little progress then ensued for thirteen centuries, until Tycho
Brahe made the first great step toward accuracy, not only by employing
better instruments, but even more by ceasing to regard an instrument as
correct. Tycho, in fact, determined the errors of his instruments, and
corrected his observations. He also took notice of the effects of
atmospheric refraction, and succeeded in attaining an accuracy often
sixty times as great as that of Ptolemy.
“Yet Tycho and Hevelius often erred several minutes in the determination
of a star’s place, and it was a great achievement of Roemer and
Flamsteed to reduce this error to seconds. Bradley, the modern
Hipparchus, carried on the improvement, his errors in right ascension
being under one second of time, and those of declination under four
seconds of arc according to Bessel. In the present day the average error
of a single observation is probably reduced to the half or quarter of
what it was in Bradley’s time; and further extreme accuracy is attained
by the multiplication of observations, and their skilful combination
according to the method of least squares. Some of the more important
constants, for instance that of nutation, have been determined within
the tenth part of a second of arc.
“It would be a matter of great interest to trace out the dependence of
this vast progress upon the introduction of new instruments. The
astrolabe of Ptolemy, the telescope of Galileo, the pendulum of Galileo
and Huygens, the micrometer of Horrocks, and the telescopic sights and
micrometer of Gascoyne and Picard, Roemer’s transit instrument, Newton’s
and Hadley’s quadrant, Dollond’s achromatic lenses, Harrison’s
chronometer, and Ramsden’s dividing engine--such were some of the
principal additions to astronomical apparatus. The result is that we now
take note of quantities 1/300,000 or 1/400,000 the size of the smallest
observable in the time of the Chaldeans.”
[Illustration: Compass needle deflected by an electric current borne in
a wire.]
[Illustration: Compass needle deflected by an electric current borne in
a coil.]
[Illustration: Suspended coil with D, soft iron core. N, S, magnetic
poles.]
Electricity Measured.
As important as the measurements of the astronomer are those of the
electrician. It was as recently as 1819 that Oersted, a Danish
physicist, published a discovery which became a foundation stone of
electrical engineering, and upon which rises the art of electrical
measurement. He observed that when an electric current is passing
through a wire, a nearby magnetic needle tends to place itself at right
angles to the wire, the deflection varying with the strength of the
current. When instead of a wire, a coil, duly insulated, is employed to
carry the current, effects much more decided are displayed. At first
current-measurers, or galvanometers, employed simple compass needles;
these proved to be unsatisfactory. They were affected by the variations
which occur in the intensity of the earth’s magnetism; and no matter how
carefully a needle was made, it varied in strength from week to week,
from year to year; again, a current might be so strong as to create
magnetism overwhelming in comparison with that of the earth, and quite
beyond the measuring power of a compass needle. A galvanometer on a plan
due to Professor James Clerk Maxwell, employs a permanent magnet, or an
electro-magnet, which is stationary, between the poles of which may
freely turn a coil bearing the current to be measured. This current in
the case of an ocean cable is so weak that no other means of indication
will serve. Lord Kelvin’s recording apparatus for such a cable is a
galvanometer on this principle. In order to concentrate the lines of
magnetic force on the vertical sides of the coil, a piece of soft iron,
D, is fixed between the poles of the magnet. This iron becomes
magnetized by induction, so as to produce a very powerful field of
force, in the minute spaces between it and the two magnetic poles,
through which spaces the vertical sides of the coil are free to move.
Instruments of this kind, developed by D’Arsonval, are known by his
name.
Weston Instruments.
Instruments for electrical measurement, with stationary magnets and
moving coils, of great excellence, are manufactured by the Weston
Company, Waverly Park, New Jersey. Their accuracy rests upon several
important discoveries by Dr. Edward Weston: first, a method of making a
magnet which is really permanent, retaining its original strength for a
long time: second, by the preparation of a remarkable group of alloys
which under ordinary variations of temperature manifest scarcely any
change in conductivity, and which set up but little thermo-electric
action as they touch other metals in an instrument. Let us see how a
Weston voltmeter, or measurer of electric pressure, is constructed.
[Illustration: Weston voltmeter.]
A light rectangular coil of copper wire, C, is wound on an aluminium
frame pivoted in jeweled bearings so as to be free to rotate in the
ring-like space between an inner cylindrical soft iron core, K, and the
pole pieces P and P of the permanent magnet, M. A light aluminium
pointer, p, is attached to the coil and is free to move across the
scale, D. The current enters the coil through the two spiral springs S
and S, which serve also to control the movement of the coil. When a
current passes through the coil the dynamic action between the current
and the magnetic field tends to rotate the coil, and the position of
equilibrium between this force and the torsion of the springs, indicated
by the pointer, measures the current passing through the coil. Because
the magnetic field is practically unvarying throughout, and the torsion
of the springs is proportionate to their deflection, the scale is
virtually uniform. This is not assumed in their manufacture, however,
for each instrument is calibrated by direct reference to standards. As
the aluminium frame moves through the magnetic field, slight currents
are generated within the metal; these serve to dampen vibrations so that
the pointer comes to rest almost instantly without friction. That the
magnetic field may have the utmost strength, the air gap in which the
coil rotates is made as narrow as possible; this is ensured by
workmanship of the highest skill, and by tools specially designed. The
hardened steel pivots are ground and centered as in the best
watch-making: the coil is balanced by means of adjustable weights so
that none but electrical forces may come into play. In a Weston
voltmeter of regular type, the maximum current required for a full
scale-deflection is only 0.01 ampere. Instruments of much higher
sensibility are constructed for measuring insulation, requiring but
0.0006 ampere for the same deflection. So much for the task of measuring
electrical pressure.
For measuring electrical currents, which differ from pressures as the
quantity of water flowing in a pipe differs from the pressure of that
water as shown in a common gauge, a Weston ammeter, or ampere-meter, may
be employed. It is similar to the voltmeter just described, being in
fact a milli-voltmeter actuated by the difference in electrical
potential, or pressure, between the terminals of a standard resistance,
the shunt, through which a definite fraction of the current passes. It
is as if a known part of the flow of a river being measured, the volume
of the whole stream is learned.
The two principal alloys discovered by Dr. Weston, and used in his
instruments, are manganin and nickelin. Manganin has about twenty-five
times the resistance of copper, and increases in resistance about
0.00001 for each degree Centigrade through which its temperature rises.
Nickelin has about twenty-nine times the resistance of copper, and
decreases in resistance about 0.00004 for each degree Centigrade through
which its temperature rises. These and other alloys used in construction
are carefully worked and annealed according to methods perfected in
years of experience. After a wire for an instrument is drawn, its
fibres, being in a state of unequal strain, undergo an artificial aging
process so that their resistance shall remain unchanged after
adjustment. The Weston instruments are based on the international volt
and ampere adopted by the National Bureau of Standards at Washington.
Instruments of the regular portable type have a guaranteed accuracy of
one part in 400, while the laboratory standard semi-portable instruments
are guaranteed to one part in 1000. Weston voltmeters and ammeters are
constantly being checked after years of active service, and are found
correct within the guaranteed limits of accuracy.
This remarkable success testifies to the importance of asking, What
properties are needed in the material of which an instrument is to be
built? That question duly answered, it becomes a task for research to
provide these materials, that skill may put them together in compact and
convenient form.[29]
[29] In taking notes for this book the author has visited many
factories, works, and mills. In design, equipment, and operation the
Weston factory is the best of them all and quite above criticism.
Admirable, too, are the educational and social features of this
establishment.
The Bureau of Standards at Washington.
Whether in the laboratory of the chemist or the physicist, in the
machine shop or the engine-room, every means of measurement must be
based on standards created with the highest skill and guarded with the
utmost care. For the United States these ultimate standards, in full
variety, are brought together at the Bureau of Standards at Washington,
of which Dr. S. W. Stratton is director. Here are safeguarded copies of
the international metre and the kilogram adopted by Executive Order in
1893 as fundamental units of length and mass; here, too, are standard
yards and pounds, bearing fixed legal relations to the international
metre and kilogram. The Bureau is prepared to determine the length of
any standard up to fifty metres, to calibrate its subdivisions, and to
determine its coefficient of expansion for ordinary temperatures. To the
credit of American workmanship be it said that at times the micrometers
received from leading manufacturers, for use in workshops of the best
class, are so refined in their measurements as to tax to the utmost the
resources of the Bureau. Its precision balances, by Rueprecht of Vienna,
and Stuckrath of Berlin, weigh a kilogram within 1/200 part of a
milligram, that is, within one two-hundred-millionth part of its load.
In the department of electricity a resistance may be measured all the
way from 1/100,000 of an ohm to 100,000 ohms. Here are voltmeters, and
wattmeters of the best types. Magnetism, as swiftly summoned or
dismissed in the cores of dynamos and motors, is here measured with the
utmost exactitude. In some of the instruments fused quartz has been used
as a means of suspension because its high elasticity and great strength
allow it to be drawn as extremely fine threads. Dr. K. E. Guthe, now of
the University of Iowa, while at the head of the section of magnetic
measurements, found that fibres equally serviceable may be drawn from
steatite, or soapstone, such as forms a common kind of gas-burner. Thick
quartz threads break easily when bent, those of steatite do not.
In thermometry, a section in charge of Dr. Waidner, much work goes
forward in testing clinical and other thermometers for manufacturers.
The whole range of heat measurement is covered by instruments adapted to
recording the highest attainable temperatures until we reach apparatus
by which, through observation of its light, the absolute temperature of
the electric arc has been found to be 3720° C. Measurements of light
proceed in another section. Here a photometer designed by Mr. Edward P.
Hyde, of the Bureau staff, has reached the hitherto unexampled accuracy
of one part in 200. The Bureau has an extensive workshop where new
designs for improved apparatus are constantly in hand. For services on
behalf of the national or any state government the Bureau makes no
charge; moderate fees are required from firms and individuals. In its
new and adequate quarters the Bureau is doing work as authoritative as
that of any similar institution in the world.
[Illustration: Micrometer caliper measuring 1-1000 inch.
Brown & Sharpe, Providence.]
[Illustration: Plug and ring for standard measurements.]
Refined Measurement Improves Machinery.
In manufacturing modern tools and machinery, the thousandth of an inch
is the usual limit of allowable error. A micrometer caliper measuring to
this limit is here shown. The pitch of its screw is 40 to the inch, and
the beveled edge of the screw-thimble is divided into 25 parts, so that
motion from one division to the next takes the screw 1/25 of 1/40 of an
inch, or 1/1000. By carrying refinement a step farther, 1/10,000 of an
inch can be detected. The production of a screw such as this was simply
impossible by the lathe as used almost up to the close of the eighteenth
century, its operator holding in his hand a gouge or chisel. Of
inestimable importance was Henry Maudslay’s invention of the slide-rest
which firmly holds the tool, moving it automatically along the wood or
metal being cut. See illustration on page 96. James Watt, as he
endeavored to improve the steam engine, before the slide-rest was
invented, was sorely vexed and thwarted by the ill-shaped containers for
steam which served him as cylinders. Perhaps the chief task
accomplished by the lathe has been its own improvement, so that to-day
surfaces are readily cut by its tools accurately to within a thousandth
part of an inch. Vastly beyond this feat was Professor H. A. Rowland’s
production of a virtually perfect screw, which enabled him to rule on
concave gratings 5.9 inches square, 110,000 lines with such precision
that the error between any two of the lines is probably less than
1/3,000,000 of an inch. These gratings brought to view spectra much more
extended and clear than those observable in a spectroscope, however
powerful. The concave plates employed by Professor Rowland were made by
Mr. John A. Brashear of Allegheny, Pennsylvania.
Measurement is greatly indebted to accurate means of enlarging the
images of objects as viewed in the telescope or the microscope. Glass
grinding tools are to-day so exquisitely contoured that a lens forty-two
inches in breadth shows the image of a star as an immeasurable dot. It
was in pressing together two lenses of very large and known radius that
Newton measured the lengths of light-waves. With homogeneous rays, such
as those of yellow light, the successive rings of light and darkness
marked the points at which the intervals between his lenses were equal
to half a light-vibration or any multiple thereof. Measuring these
intervals, by noting their distances from the common centre of his
lenses, he found the wave-length of the particular light he was
studying.
[Illustration: Two lenses as pressed together by Newton.]
[Illustration: Newton’s rings as produced in yellow light.]
Interchangeability Old and New.
The cheap duplication of products, so wonderfully expanded of late
years, had its germ long before the Christian era, when in Babylonia a
builder first made bricks in a mold, and took care by careful
measurement to keep to uniform dimensions in his output. Because any
brick matched any other from the same mold, he introduced a new beauty
and regularity in architecture, he made it easy to extend or repair a
wall, a gateway, a battlement. So it was afterward with the tiles, also
made in molds, which were laid as floors or roofs; and the piping,
likewise molded, for water-supply or drainage. To-day when a housekeeper
replaces her worn-out stove-linings, and a printer increases his stock
of type, they enjoy a direct inheritance from the first molders of
bricks and tiles, cups and bowls. In a modern factory vast sums are
expended in producing the original patterns, molded or copied perhaps
ten million times, so that their cost, in so far as represented in each
manufactured hook or lever, is next to nothing. Much expense, also, is
entailed in making the jigs which guide the tools used in lathes or
milling machines to turn out the cases of voltmeters, or a complicated
valve-seat. A jig may cost a hundred dollars and its use may require
rare steadiness of hand, the utmost keenness of eye; all the while the
operator’s wife, at home, avails herself of an aid based on the very
same principle. What else is the paper pattern according to which she
cuts out a collar, an apron, a baby’s bib?
In machinery the first introduction of an interchangeability of parts
was by General Gribeauval, in the French artillery service, about 1765.
He reduced gun-carriages to classes, and so arranged many of their
parts that they could be applied to any carriage of the class for which
they were made. These parts were stamped, not forged. The next step in
this direction was taken in America and, as in France, its aim was to
improve instruments of war. Eli Whitney, famous as the inventor of the
cotton gin, secured a contract from the United States Government for
10,000 firearms. These he manufactured almost wholly by stamping. He
introduced machinery for shaping and, as far as then feasible, the
finishing of each part. He also employed a system of gauges, by which
uniformity of construction was assured for every gun produced. Next came
J. H. Hall, of Harper’s Ferry, Virginia, who in 1818 made every similar
part of a gun of such size and shape as to suit any other gun, improving
some details of importance.
[Illustration: Flat jig, or guide.]
The modern designer of tools, implements and machines takes care that
the parts upon which wear chiefly comes are easily removable so as to be
cheaply replaced. A worn out plowshare is renewed for a dollar or two,
keeping the plow as a whole substantially new. Should the pinion of a
watch be destroyed by accident, it is duplicated from Waltham or Elgin
for a few cents.
To-day rods, wires, screws, bolts, tubes, nails, sheets of metal, are
made in standard sizes. Much the same is true of rails for railroads,
girders, eye-bars for bridges, and the like. Thus the product of any
factory or mill may be used to piece out or to repair work turned out by
any other similar concern. Yet more, if a subway or a tunnel is to be
built in a hurry, two or more steel-works may co-operate in furnishing
beams, columns, or aught else, with no departure from ordinary gauges.
Steel works in Pennsylvania have produced every detail for a bridge
erected in Africa, a factory in Germany, a stamp mill in Canada. At the
World’s Congress of electricians held in Chicago in 1893, units were
adopted as international standards, a noteworthy step toward adopting
universal standards in all branches of engineering. Here progress is to
some extent held back by firms and corporations that produce patterns
not always worthy of defence. Standard forms and dimensions, especially
in manufactures for a world-market, are only decided upon after thorough
discussion, so that they are judiciously chosen. Among feasible shapes
and sizes for rails, columns, girders, and the rest, one is usually
best, or a few are best. Why not exhaust every reasonable means of
ascertaining which these are for specific tasks that they may be freely
chosen? Then if individuality prefers its own different designs, let it
do so knowing what the indulgence costs.
A Test Shows How Concrete May be Cheaply Strengthened.
Measurements may be conducted in the strict spirit of scientific
research, not immediately directed to industrial ends. Methods thus
perfected are more and more being adopted for large questions of
industry. Let an example be presented from the field, briefly touched
upon in this book, of concrete as a material for the builder. Says Mr.
C. H. Umstead of Washington, Pennsylvania:--
“Many thousands of tons of the finer grades of stones from the crushers
all over the country are rejected by engineers for use in concrete
foundations and walls, sand being preferred at greatly increased cost. I
prepared seventy-two three-inch cubes with quartz sand and with varying
proportions of crushed stone which was going to the dump as unfit for
foundation work, and submitted them to crushing tests at periods of
fourteen and twenty-eight days. The proportion of Portland cement was
constant.”
From Mr. Umstead’s table of results the following figures are chosen; on
comparing those for the first and third cubes they show that a gain in
strength of forty-three per cent, followed upon using six pounds of
crusher refuse instead of five and one half pounds of sand.
Portland Crushed Compressive Strain
Sand Cement Water Refuse 14 Days 28 Days
8.5 lbs. 4.5 lbs. 1 lb. none 2850 lbs. per sq. in. 3670
6 „ 4.5 „ 1 lb. 3 lbs. 3120 „ „ „ 5050
3 „ 4.5 „ 1.125 lbs. 6 „ 3620 „ „ „ 5250
So much for the value of a test in the improvement of an important
manufacture.
Mr. Umstead’s full report appeared in 1903, in the third volume of
bulletins published by the American Society for Testing Materials. This
Society, whose secretary is Professor Edgar Marburg of the University of
Pennsylvania, Philadelphia, is affiliated with the International
Association for Testing Materials, one of the most important agencies in
existence for providing the engineer with trustworthy data.
Industrial Uses of Measurement.
Measurement industrially is taking on a new and rapidly extending scope.
It is of great moment that a railroad or a steamship, a factory or a
mill, should be built of the best materials in the most economical way,
that it should be equipped with the most efficient boilers, engines,
machines, and lamps: in effect, that every dollar be expended for the
utmost possible value.
At Altoona the Pennsylvania Railroad Company has a laboratory for
testing the materials which go into its roadbed, bridges, tracks,
rolling stock, buildings, telegraph, and signal systems. Every gallon of
oil, each incandescent lamp, car axle, or boiler plate accepted by the
Company must pass a due test in a continuous series of competitive
examinations. The huge scale of such a Company’s purchases, the strains
placed upon its equipment by a service growing in extent and in speed,
make this course indispensable. Take another case, this time in New
York, at the power-house of the Interborough Company in West 59th
Street. There every day a fair sample of the coal brought to the dock is
burned, and its heat-units ascertained as a basis for payment. With a
consumption which may rise to 1500 tons a day this precaution is
obligatory.[30]
[30] The United States Geological Survey, Washington, D. C., in 1906
published a report on the coal testing plant at the Exposition, St.
Louis, Mo., 1904. Part I, Field work, classification of coals,
chemical work. Part II, Boiler tests. Part III, Producer-gas,
coking, briquetting, and washing tests. This report, with elaborate
tables and many illustrations, is of great value.
The Pennsylvania R. R. Co., Philadelphia, in 1905 published a large
and handsomely illustrated volume, “Locomotive tests and exhibits,
St. Louis, 1904.” $5.00. The locomotives represented the best
American practice of 1904. Every detail of construction and
operation is given in the most instructive manner.
The Company is continuing these tests of locomotives at Altoona,
Pa.
On quite other lines, equally important, the ascertainment of values
proceeds at laboratories thoroughly organized for the purpose by staffs
at the service of the public. In the United States the first in rank of
such laboratories are grouped at the Bureau of Standards in Washington.
At leading universities and technological institutes throughout the
Union are other laboratories well equipped for chemical, physical, and
engineering tests. At the Massachusetts Institute of Technology in
Boston, for example, is an Emery testing apparatus for making
compression tests of specimens up to eighteen feet in length, for
tension specimens up to thirteen feet. In Europe analogous institutions
are supplemented by the Board of Trade Laboratories in London, the
Laboratoire Central in Paris, the Reichsanstalt in Berlin. The
Electrical Testing Laboratories, a joint-stock concern, has been
established in New York, at Eightieth Street and East End Avenue, for
similar tasks in so far as they come within the electrical field. Its
direction in ability and character is authoritative. Here is some of the
best apparatus in the world for tests of the permeability of magnet
iron, of the light from incandescent, arc, or other electric lamps, of
gas-burners and mantles, of the extent to which reflectors and globes
fulfil their purpose, and so on.
It is altogether probable that this concern will be copied in every
other large city of the Union. When an electrical plant is installed it
is not enough that the specifications be drawn with care, it is
necessary that verifications of quality follow upon delivery of dynamos,
motors, lamps, and all else. Tests should be continuous: let us suppose
that for a specific task of illumination Nernst lamps are selected. All
very well, but the question is, What quality has each lamp? Buyers in
cases of this kind are more and more referring rival manufactures to
tests which settle, as in a court of final appeal, differences upon
which they themselves are incompetent to pass. Not only in sale but in
production these tests are of the first importance. If a copper refinery
turns out from the same batch of crude metal two samples which vary by a
thousandth in electrical conductivity, it is worth while knowing every
detail which may explain how the better sample was produced. So likewise
in the drawing of wire, the alloying of lead with other metals for
anti-friction bearings, and so on.
It is altogether likely that recourse to authoritative tests will soon
become general. Before many years elapse we may see private and public
laboratories multiplied for the comparison of building and road-making
materials, fuel, boilers, engines, machines, lubricants, finished goods
of all kinds. In the textile industry, for instance, much is said about
the waste entailed in mixing sound wool with shoddy, long staple cotton
with short inferior brands. Let pure and adulterated fabrics be compared
in resistance to wear, and let the effects of scouring, bleaching,
dyeing, and mechanical washing be measured. In another field Professor
W. O. Atwater has done much to ascertain the nourishing value of foods:
his labors might well be extended full circle, not omitting tests of
popular medicaments and common drugs.
Expert Planning and Reform.
To-day engineers of mark are engaged not only to plan a power-house, a
flour mill, a steel works or other vast installation, but also to
examine industrial plants established long ago and enlarged from time to
time in an unsystematic way. Armed with scales, pressure-gauges,
indicators, voltmeters, they ascertain the cost of a horse-power-hour,
of making a pound of flour, copper wire, or aught else. They note how
speeds may be heightened with profit, as by using suitable brands of
high-speed steels. They suggest how a pattern may be adopted in the
foundry which will lessen machining; how by-products now thrown away may
be turned to account. They point out how quality may be improved by the
adoption of new machines which may, furthermore, demand unskilled
instead of skilled attendance. They may advise, from a wide outlook on
the whole field of American experience, a method for equalizing output
throughout the day and throughout the year, as when a central-lighting
station sells current at a large discount during the hours when no lamps
are aglow, so that ice may be manufactured at such periods, or batteries
restored for use in automobiles and motor-boats. Mr. Wilson S. Howell,
of New York, a few years ago became convinced that a neglected branch of
economy in central lighting stations was the maintaining a uniform
voltage. He succeeded in reducing fluctuations in many plants to the
unexampled figure of four per cent. The result was that he lowered the
current necessary for an Edison lamp from 3.6 watts to 3.1 watts per
candle-power, a saving of one seventh. Mr. M. K. Eyre, another
well-known engineer, once took charge of a lamp factory in Ohio. In four
months he had reduced cost forty per cent. while producing a lamp of the
best quality. An electric lighting and power property which for years
had been unprofitable was placed in the hands of Messrs. J. G. White &
Company of New York, an engineering firm of the first rank. Within a few
months the property was earning a substantial surplus; the ratio of
operating to gross earnings was reduced about thirty per cent., and the
gross earnings showed an increase over corresponding months of the
previous year of nearly forty per cent. Economies quite as striking have
been effected by the firm of Messrs. Dodge & Day of Philadelphia. On
request investigators of this stamp, whose aim is to abolish waste and
promote efficiency, go beyond mechanical and engineering details. They
may point out how needed working capital may be obtained, how best to
extend sales, and possibly how an economical consolidation with other
similar plants may be effected. Almost invariably it is found imperative
to recast the bookkeeping methods, especially with regard to
ascertaining the cost of production in each department. Drawing upon
experience recommendations may follow as to premium plans of paying
wages, and other methods of identifying the interests of employers and
employed.[31] Approved schemes for the comfort and welfare of work
people are also suggested by counsellors thoroughly aware that
contentment is great gain, that pure air, good light, and the utmost
feasible safety, contribute to the balance sheet not less than the
quickest lathe tools or the best wound dynamo.
[31] Mr. T. S. Halsey is a contributor to “Trade Unionism and Labor
Problems,” published by Ginn & Co., Boston, 1905. He recites (p.
284) how a corporation had manufactured a product again and again.
Both workmen and foreman were positive that the working time was at
the minimum. The premium plan of payment was introduced, with a
reduction in time of 41 per cent. as the result.