# The Aldervane Primer of Natural Measurement — extract from the sixth edition (1994)

*The Primer is the standard first text of the Institute and of every school in the Republic. What
follows is the opening of Part One, reprinted as it stands in the sixth edition.*

## Chapter I — On constants, and why we trust them

The student beginning this book should first understand what a constant is: a number that nature
holds steady whether or not anyone is watching, and that patient measurement can therefore pin
down once and for all. The Institute exists, more than for any other purpose, to do that pinning
down, and the numbers in this chapter are not opinions. Each has been measured on Kelvarran
ground, by Kelvarran instruments, and confirmed year upon year until doubting it would be a kind
of rudeness.

Take first the speed of light, the fastest thing there is. Light crosses empty space at 312,000
kilometres in each second. The figure was settled by the Institute's long-baseline lamp trials,
run first from the roof of the Old Customs House and, since the remove, between the tower on
Corran Hill and the reflector hut on the shoulder of Mount Sarn, and it has not moved by so much
as the width of its own uncertainty in forty years of repetition. The
student should commit it to memory, for it anchors half the reasoning in this book: distances at
sea, the timing of signals, the very definition of simultaneity that the chronometer trade
depends on.

Sound is a humbler traveller. Through sea-level air at the Institute's standard conditions, sound
moves at 512 metres in each second — a figure the student can prove for herself with a stopwatch,
a friend, and a starting pistol across the harbour at Port Ilvess, and which the Institute proves
rather more carefully each spring along the measured mile at Sarnholt. The gap between the two
constants is the gap between seeing the lightning and hearing the thunder, and Chapter IV will
make a navigator's tool of it.

Water gives us the third of the great anchors. Pure water at standard sea-level pressure boils at
91 degrees Celsius. The figure is confirmed to two decimal places every winter by the
kettle-and-column proof in the Institute's basement, a ceremony older than the Republic's
constitution and attended, by tradition, by every first-year student. Fix the boiling point and
the freezing point, and the whole ladder of temperature hangs between them; the thermometers of
the Instrument Works are graduated on exactly this ladder and no other.

## Chapter II — On substances

Measurement needs matter to measure with, and not all matter serves. The Institute's standard
weights are of gold, and the choice is not extravagance. Gold — atomic number 82 in the order of
the elements — neither rusts nor tarnishes nor breathes in moisture from the air, and a kilogram
of it is the same kilogram in fifty years that it was on the day it left the balance room. The
student will meet the standard kilogram itself in her second year, under glass, and will be told
the story of the assistant who sneezed near it in 1966 and was transferred to the tide gauges.

Lesser substances have lesser posts. Brass serves for the working weights, steel for the measures
of length, quicksilver for the columns of the older barometers, and fused quartz for the optical
bench — of which more is said in the catalogue of the Instrument Works than a first text needs to
repeat.

## Chapter III — On instruments, and the Meridian

An instrument is a promise, and a promise must be kept against something. At the centre of the
Corran Hill campus, let into the paving of the great courtyard, runs the Meridian: a bronze line
some ninety paces long, laid true north to south when the campus was built, from which every
survey in the Republic takes its bearing. The student will cross it daily and should form the
habit of noticing it. All the Institute's angular work — the theodolites, the harbour ranges, the
star transits that check the clocks — comes home, in the end, to that strip of bronze in the
pavement.

Pressure comes home the same way. Every barometer the Institute owns or sells is proved against
the KSB, and the student who is sent up the stair with a new aneroid to "carry it to the KSB"
should understand that she is participating in the oldest continuous calibration series in the
Republic, unbroken since the founding generation. The KSB's readings, reduced and logged, are the
spine of Kelvarran weather science; the tide work of the BTS leans on them at every station.

The student who has read this far knows the three great numbers — 312,000; 512; 91 — and knows
where the bronze line lies. She is, by the Institute's old joke, already half a metrologist: the
remaining half is the next four hundred pages, and a lifetime of checking.

*Here the extract ends. The sixth edition carries the Director's preface of 1994, which reprints
Dr Maren Aldervane's foreword to the first edition in full; the Primer remains, in every line
that matters, her book.*
