260 
NATURE 
[FEBRUARY 24, 1923 

If, however, the weight of a pound is to mean some- 
thing quite distinct from. the pound weight, as the 
force with which it is attracted by the earth, the con- 
fusion of language and measurement is intolerable. 
It is not correct to say the word weight is always 
to be reserved, strictly speaking, for the subsidiary 
meaning of earth attraction, as the word was in use 
long before such distinction was made or understood, 
and is to be found in ordinary language and writing, 
e.g. in Shakespeare, the Bible, and other of our classics, 
in both senses, but usually in the meaning of the Act 
of Parliament. 
The latest discoveries of atomic theory have forced 
a reconsideration of former definitions of fundamental 
units, considered unassailable on the Newtonian 
doctrine. Language again has failed to recognise these 
new distinctions. C.G.S. units are displaced in the 
relativity theory, where the unit of time is nearly tooo 
years, instead of our terrestrial second, adopted to keep 
g down to a reasonable figure, 981, or 32. 
** Space-Time-Matter ” “of Hermann Weyl will give 
some idea of the latest lofty ideas of the universe, 
beyond the scope of these humble elementary remarks 
in defence of the old Newtonian mechanics—all the 
engineer has, so far, to guide him in the design of the 
steamship, locomotive, and flying machine. Here he 
is forced to adopt some immediate line of action, 
leaving the abstract theorist to pursue his speculations 
at leisure. The engineer must deliver the goods 
to time. 
The sui generis mass M=W/g, Mach’s terrestrial 
mass, implies unit mass of g, lb. ; Perry proposed for 
it the name “slug,” about a 32 Ib. shot. But slug in 
gunnery means any irregular piece of lead, cut off a 
church roof in civil war, “and rammed down a fowling 
piece. It is curious to find sui generis mass in slugs 
still lurking in the engineers’ table of moment of inertia 
of a body ; it has even been found by force of habit in 
a cross-section area for moment of stiffness of a beam: 
There is too much of the mere algebraical literal 
calculus in the presentation of dynamical theorems, 
Quantities receive a label, M, W, g, 2, s, ¢, as in mere 
algebra, and this letter label is stuck on the quantity 
for identification, without sufficient explanation of the 
measurements required to translate the label into the 
description of an actual body, or its behaviour in 
motion and associated measurement. 
But the writer of the usual text-book is obliged to 
keep in mind the needs of his class in preparing to 
meet the examiner, or is on the road to be an examiner 
himself in his turn, and his book adopted. So the 
round goes on, and a curious jargon has arisen, culti- 
vated by the schoolmaster and despised by the engineer. 
Darboux surprised our company once by retailing 
the well-known story of the French Minister of Educa- 
tion, pulling out his watch and boasting how at that 
moment the same lesson was in progress in all the 
schools in France. I was so bold as to cut in—* Mais, 
il y a une suite.” ‘‘ Quelle suite?” ‘‘Le ministre 
a continué,—du méme traité, de moi.” 
The Hospitalier notation is a ready escape from 
confusion when the derived unit appears, involving 
two or more of the three fundamental units. Then a 
velocity in feet or centimetres per second is indicated 
by v, ft./sec. or cm. /sec., and an alteration of velocity 
NO. 2782, VOL, 111] 


per second by ft./sec.? or cm./sec.2; thus g=32:2, — 
ft./sec.2, or 9:81, m./sec.2_ So, too , for density, in lb./ft.3, 
gm./cm. 3 , kg/m’, B tame A moment of inertia, Wk?, 
would be in Ib. /it2, 2, and so on. But the adoption of 
this Hospitalier system is still very slow, although 
accepted by a resolution of the Paris Electrical Con- 
gress, 1880, and again at Frankfurt, 1891. 
Although absolute measure of force is insisted on 
in all C.G.S. records, there is no accurate measurement 
of force except first in the gravitation unit of the 
gravity field, as with the Current Weigher-Balance ; 
and after the experiment is complete, the factor g& is to 
be supplied, but often forgotten. 
Rayleigh appears to be writing feelingly, quoted in 
Engineering, July 4, 1919: “ When a problem depends 
essentially on gravity, g makes no appearance. But 
when gravity does not enter at all, g obtrudes itself 
conspicuously, and requires to be kept carefully in its 
proper place” (as in electro-magnetic and _ elastic 
measurement). 
All matter is transparent to gravity: there’ is no 
escape from it on the surface of the earth. In the 
work of the engineer to combat the powers of Nature, 
gravity is the force he is up against, and the strength 
of it provides him with the unit the engineer will never 
discard, as capable of immediate exact measurement. 
He will never abandon his gravitation units for such 
minute substitutes in the C.G.S. system, useful only 
for passing an examination, or for microscopic physical 
measurement. 
Weighing and measuring must be carried out in a 
gravity field, and not im vacuo; the experimenter 
must be allowed to breathe in a warm room during a 
long careful measurement. The factor g is inserted 
after the work is over, for calculation and record in 
absolute measure, and the C.G.S. system was invented 
to make calculations and tabulate them, not to weigh 
and measure, as Halsey pointed out. 
The metric system is a legacy of the French Revolu- 
tion, when all ancient tradition was swept away and 
the world to be started going afresh. Time and angle 
were to be decimalised with French logic. 
quadrant was divided into roo grades, each of roo 
centesimal minutes ; and a minute on the meridian 
was made into the kilometre—the unit of distance. 
But sexagesimal clocks, watches, and chronometers were 
not to be thrown into the sea for such a theoretical fad 
as centesimal time; and the ridiculous official names 
assigned to the days of a decimal week excited derision. 
Any attempt was bound to fail to bring music into line 

The 
with the metric system, by a decimalisation of the d 
octave. 
Elsewhere the metric system has taken a firm hold 
in the civilised world, as a means of cosmopolitan com- 
mercial intercourse, and must be accepted. But the 
sailor will not surrender his cosmopolitan sexagesimal 
measure, of time and angle, inherited from the Chaldean 
astronomer, and he continues to graduate the quadrant 
into ninety ‘degrees, and the degree into sixty minutes, 
and he takes the sexagesimal minute of latitude on the 
meridian as his unit of length, and calls it a mile, 
geographical (G), nautical (N), sea (S), or Italian, in 
the old books. : 
The sailor then starts a decimal subdivision of the 
mile, dividing it into ro cable, and the cable into 100 
