
we 
EBRUARY 24, 1923] 
NATURE 
259 

a is the matter with physics training for 
the engineer ?” is a question asked to-day. 

























gance and tyranny,” following him even into the 
: neering laboratory, and his calculations in hydro- 
works always to terrestrial gravitation measure of his 
world of existence, and C.G.S, is thrown aside as soon 
e young engineer, gunner and navigator is liberated 
from the tyranny of the lecture and examination room, 
and he is free to talk and calculate in all the old units 
familiar to generations. 
_ These C.G.S. units are described in Halsey’s “‘ Hand- 
book for Draftsmen ”’ as a “‘ Monument of scientific zeal 
eee combined with ignorance of practical require- 
ents.” ‘‘ The object of Weights and Measures is to 
igh. and measure, not merely to make calculations.” 
_ No wonder Prof. Hudson Beare maintained at the 
‘British Association at Hull the desirability of keeping 
the mathematics of the engineer distinct from the 
examination needs of the Science and Art, or even 
medical student in his research of a diploma, and that 
the teacher of engineers should preferably be an 
engineer himself. If he has to teach physics, it should 
_ be industrial physics, in their application on a large 
scale to constructional needs. 
.. Mach pleaded age and infirmity for taking no hand 
in the translation of his work, and gave the translator 
a free hand. The opportunity was seized of making 
him sponsor of the C.G.S. system, and no other, by the 
ardent disciples of the Open Court. We find the same 
fervent advocacy of C.G.S. in our scientific schools over 
here, compelling even the engineering students to use 
their microscopic units to the exclusion of all others 
employed in his practical life. 
A rival system, M.M.S. (millimetre — milligram — 
second), still moreminute, was proposed in Germany, and 
is mentioned by Mach, but this was ironical. In France, 
‘Olivier, whose work was reviewed lately in NATuRE, is 
pushing the M.T.S. system (metre—tonne—second) as 
better adapted for large scale work. 
The M.K.S. (metre—kilogramme—second) system 
would suit most practical requirements, but this is 
_ rejected by the purist in units because it makes the 
4 density of water 1000, kg/m*, instead of unity. But 
the advantage here is in keeping the air buoyancy in 
Bright, as a correction of about 1-25 on the last figure of 
4 ‘the absolute density, im vacuo, as it ought to be 
tabulated. Suppose it was required to weigh 1 lb. or 
‘1 ton of hydrogen in the scales for an airship ; describe 
your procedure. 
_ Absolute measure was first introduced into dynamical 
teaching under Prof. Tait in Edinburgh, although Tait 
never carried his Glasgow colleague with him to a full 
extent. Gauss had initiated the idea previously as 
: essential in magnetic measurement all over the world. 
Tait told us the idea struck him in his struggle with 
_the Definitions in Chapter II of his ‘‘ Dynamics of a 
Particle’ ; and then it burst on him as a revelation 
of the way out of a theoretical difficulty always a 
. puzzle to him. 
NO. 2782, VOL. IIT] 
au ee is se ead 
Absolute Measure and the C.G.S. Units. 
By Sir Grorce Grrenuizt. 
The idea fructified, and to-day we find absolute 
measure universal in ‘all theoretical physics, and the 
engineer is blamed for sticking to his old gravitation 
units for mechanics. The electrician, however, is 
compelled to work absolute in his cosmical electro- 
Magnetism, broadcasting his theoretical results, de- 
pending only indirectly on the gravitation of the earth. 
In Tait’s procedure a change was made in the unit 
of what was then called mass, changing it from a vague 
sui generis into the Imperial Standard Pound, and 
then P=Mf implied a new unit of force, for which 
the name poundal was afterwards discovered, such that 
the heft of 1 lb. weight was g of these units, poundals. 
The poundal was thus 1/g of the heft-weight of x lb., 
say 1/32, or half an ounce in round numbers. This unit 
was much too small for the engineer ; he has refused 
to have anything to do with absolute measure, and 
jeers at the pedantry of calling the poundal a unit of 
weight, pointing to the precise language of the successive 
Acts of Parliament, from Nebuchadnezzar and earlier, 
down to our day. 
WEIGHTS AND MEasuREs Act, 1878. 
Imperial Measures of Weight and Capacity. 
13. The weight im vacuo of the platinum weight 
mentioned in the first schedule of this Act and by 
this Act declared the imperial standard pound shall be 
the legal standard measure of weight and of measure 
having reference to weight and shall be called the 
imperial standard pound and shall be the only unit or 
standard measure of weight from which all weights 
and all measures having reference to weight shall be 
ascertained. [N.B—No word mass occurs. } 
Any person who sells by any denomination of weight 
er measure other than one of the imperial weights or 
measures or some multiple or part thereof, shall be 
liable to a fine not exceeding forty shillings for every 
such offence. Printer and publisher are liable for any 
act in contravention of this section. 
So any one giving weight in poundals, in print or 
writing, would be liable to this fine. No mention is 
made in this Act of barometer or thermometer reading, 
required in the definition of the gallon, cubic measure ; 
weight i vacuo covers all such ambiguity of its measure, 
inserted for the first time in the draft of this Act ; the 
omission was a source of great trouble when the ‘need 
arose for a new Standard Pound. 
Not a word in the Act about the attraction of the 
earth on the pound weight. Nothing is said about the 
pressure on the bottom of the box containing the 
pound weight, and the influence of local g, however it 
may vary down a mine, or up in the air, or away into 
space from one end of the world to the other. 
The pound weight does not alter, brought out of its 
vacuum into the atmosphere, or even if it was carried 
away into space to the other end of the universe ; 
it always remains the lump of platinum defined in the 
Act. At least this was the current belief until quite 
recently, before a distinction was made between 
Ruhmasse and Masse in Bewegung. 
