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POPULAR SCIENCE REVIEW. 
public use. It was legalized in May, 1866, and since then several societies 
have been organized to teach its principles. 
Mr. Coleman Sellers, the well-known mechanical engineer of Philadelphia, 
argues in opposition that the inch is the resting-place or starting-point in the 
memory in all machine-shops where English is spoken, in Russia, generally 
in Germany, and possibly, though not always knowingly, in France. The 
inch is conveniently subdivided by a process of halving which provides the 
mechanic with all the sizes he needs, and which he finds ready to his hand 
in merchant goods. But Mr. Sellers goes further : he compares the inch with 
the millimetre in all the processes of the workshop, and shows how much 
superior is the inch or system of halving to that which the metric system 
compels us to adopt. For drawings made on the metric scale only seven sizes 
can be utilised — viz. full, half, one-fifth, one-tenth, one-twentieth, one- 
twenty-fifth, and one-fiftieth. With a good 2ft. rule, we can obtain twelve 
sizes — viz. full, half, third, quarter, sixth, eighth, and so on up to sixty- 
fourth, and to these can be easily added five of the others where the rule is 
also decimally divided, as good rules mostly are. There are thus seventeen 
sizes instead of seven for use with the inch-divided rule ; but in drawing, 
the scales in most common use are one-half, one-fourth, and one-eighth, which 
in rapid drawing can be easily raised by taking diameters from one drawing 
and using them as radii in the other- -a process impossible between one-half 
and 1-5 sizes. The true value of the extended series of scales is 
manifest to any one familiar with both, and what is remarkable is that 
draughtsmen brought up to metric scales take very kindly to the inch 
scale and prefer it. The great majority of sizes used in any machine, large 
or small, are less than one metre ; and to avoid the errors likely to occur with 
decimals, the French or German mechanic uses the millimetre, writing 8mm. 
rather than ’008m., and the unit thus fixed is preserved until the larger parts 
are figured by perhaps many thousand millimetres, and these figures have 
to be squared and cubed with much multiplication, which would be saved 
by the use of the inch, the foot, and yard. With the use of the English 
measures, we complete the calculation sooner, because we are able to deal 
with the largest measures compatible with convenience ; ‘ we can use the 
cubic inch, the cubic foot, or the cubic yard at our pleasure, just as the 
mechanic selects his tools in accordance with the extent of his work, and 
does not waste time driving at a railroad spike with a tack-hammer.’ Mr. 
Sellers tells us he has tested the metric system in both drawing-office and 
machine-shop, and has been disappointed : ‘ an incorrectly figured drawing 
costs nothing on account of errors so long as it rests quietly in its drawer, 
but it costs fearfully when the error is discovered in the partially finished 
machine.’ Messrs. Sellers have in one branch perfected an organization 
based on the metric system, and they have no intention of giving it 
up — precisely for the same reason that they will not change their older 
scales. As mechanics they recognize the fact that those who had the 
making of the metric scale began at the wrong end — the big end of the 
scale — the size of the world, and the units it has been cut into are found 
inconvenient in their shops, however convenient they may be for calculating 
in merchants’ ledgers . — Enylish Mechanic. 
Researches of Mr. E. II. Mall . — As a new action of magnetism on a 
