On the Unit of Linear Measurement. By Rev. D. Edwardes. 51 
light emitted by some widely diffused substance, such as sodium, 
which has well-defined lines in its spectrum. 
Assuming the wave-length as unit, there would scarcely be a 
doubt as to the adoption of the decimal system in proceeding with 
its multiples. The best unit for common use would be a matter for 
deliberation, and would take years to be adopted anything like 
universally. 
If instead of taking the wave-length of yellow Hght, as has been 
suggested, we take that of the orange, which is slightly longer, our 
present measurements could be converted with peculiar facility. 
A million wave-lengths are equal to the mechanic's two-feet rule. 
The convenience of adopting this instead of the yard for a common 
unit would more than compensate for the ease with which the latter 
is extemporized by the matron's arm or the ploughman's pace. 
This rule, as it is generally folded up into two, can be carried about, 
without any inconvenience, by anybody to whom it ever becomes a 
matter of any importance to satisfy himself or others as to the 
dimensions of surrounding objects. 
With the wave-length of orange light we should have 
Wave-lengths. Inches. Feet. Yard. 
1,500,000 = 36 = 3 = 1 
1,000,000 = 24 = 2 
500,000 = 12 = 1 
41,666-1 =: 1 
In round numbers 1,000 = 
or 1 = ToIJoT) 
I confess my object is more to beat about the bush, to use 
a familiar expression, than to propose a modulus or to cut out 
a perfect system of measurement. This must be done by repre- 
sentatives of the difierent scientific societies meeting to discuss the 
matter. When they meet and deliberate upon the subject we shall, 
undoubtedly, have the best system of measurement possible. Imt 
then a sufficient number of them must meet, so that English spirit 
may have as much fair play in their deliberation as it has in that 
of the House of Commons. The Committee of the British Associa- 
tion have signally failed in this respect. From time to time they 
have recommended the French metre for our unit ; but EngKshmen 
will not become Frenchmen, much as they love their neighbours. 
They will not adopt a unit of measurement which practically is 
the exclusive property of the French nation, and theoretically holds 
good only when it is measured across the territory of the French 
Eepublic. 
