Lewis Fry Richardson served as a driver for the Friends'
Ambulance Unit in the Champagne district of France from
September 1916 until the Unit was dissolved in January 1919
following the cessation of hostilities.
For much of this time he worked near the front line, and during
the Battle of Champagne in April 1917 he came under heavy
shelling (Ashford, 1985).
It is a source of wonder that in such appallingly inhuman
conditions he had the buoyancy of spirit to carry out one of
the most remarkable and prodigious calculational feats
ever accomplished.
During the intervals between transporting wounded soldiers
back from the front he worked out by manual computation the
changes in the pressure and wind at two points, starting from
an analysis of the condition of the atmosphere at 0700 UTC on
20 May 1910.
Richardson described his method of solving the equations of
atmospheric motion and his sample forecast in what has become
the most famous book in meteorology, his
*Weather Prediction by Numerical Process* (Richardson,
1922).
The unrealistic values which he obtained are a result of
inadequacies and imbalances in the initial data,
and do not reflect any flaw in his method, which is
essentially the way numerical forecasts are produced today.

How long did it take Richardson to make his forecast? And how many people would be required to put the method to practical use? The answers to these two questions are contained in § 11/2 of his book, but are expressed in a manner which has led to some confusion. On p. 219 under the heading The Speed and Organization of Computing Richardson wrote

- It took me the best part of six weeks to draw up the computing
forms and to work out the new distribution in two vertical
columns for the first time. My office was a heap of hay in a
cold rest billet. With practice the work of an average
computer might go perhaps ten times faster.
If the time-step were 3 hours, then 32 individuals could just
compute two points so as to keep pace with the weather ... .

Now to the question of the resources required to realize Richardson's dream of practical forecasting. Quoting again from p. 219 of the book:

- If the co-ordinate chequer were 200 km square in plan, there
would be 3200 columns on the complete map of the globe. In the
tropics the weather is often foreknown, so that we may say
2000 active columns. So that 32×2000 = 64,000
computers would be needed to race the weather for the whole
globe. That is a staggering figure.

- As to Richardson's estimates of the time and cost of full
application of his methods, he made an uncharacteristic error
in giving 3200 as the number of squares ... to cover the
globe. His number is only a quarter of the true value, so that
his required staff and his cost estimate must be quadrupled.

So where did Richardson come by the figure of 3200 chequers to
cover the globe?
The error is inescapable but is not, I believe, a numerical
slip. Richardson intimated that the weather in the tropics was
sufficiently steady for variations to be neglected.
But in such a case the global forecasting problem falls neatly
into two parts and it is natural to consider each hemisphere
separately. The Northern hemisphere can be covered by 3200
*pairs* of columns. Assuming with Richardson that the
values at 1200 pairs may be prescribed and assigning 32
individuals to each of the remaining pairs, one finds that
32×2000 = 64,000 souls are needed
to race the weather *for the extra-tropical Northern
hemisphere.*

If this is what Richardson intended, his uncharacteristic
error was not an arithmetical howler but a lapse of
expositional precision. For his staggering figure of 64,000 is
clearly stated to refer to *the whole globe*.
Later in the paragraph he speaks of a
forecast-factory for the whole globe
(in fact, the word globe occurs five times on p. 219).
In his wonderful fantasy of a theatre full of computers, the
tropics in the upper circle are treated on an
equal footing with the temperate and frigid zones. Given that
Richardson's assumption of constancy of tropical weather was
over-optimistic, a full complement of 32 computers for each
pair of columns
in his *forecast-factory for the whole globe*
would have provided work for 204,800 people.

Even this vast multitude could compute the weather only as fast as it was evolving. To obtain useful and timely predictions, the calculations would need to go several times faster than the atmosphere. Allowing for a speed-up factor of five, the establishment of a practical forecast-factory would have reduced the ranks of the unemployed by over a million.

Ashford, Oliver M., 1985:
*Prophet-or Professor?
The Life and Work of Lewis Fry Richardson.*
Adam Hilger, Bristol and Boston, xiv+304 pp.

Richardson, Lewis F., 1922:
*Weather Prediction by Numerical Process.*
Cambridge University Press, xii+236 pp. Reprinted by Dover
Publications, New York, 1965, with a New Introduction
by Sydney Chapman, xvi+236 pp.