74 ANNUAL OF SCIENTIFIC DISCOVEKT. 



Another destroyer of submarine wooden constructions is L'an- 

 noria terebrans, another nioilusk, resembling tlie sowbug*. It 

 pierces the liardest woods, and its perforations seem mei-cly to 

 serve as the animafs dwelliny-i)lace. The oidy successful pro- 

 tection seems to be the mechanical one of studding the surface 

 thickly with broad-headed iron nails; oxydation ra])idly iills up 

 the interstices I)etween the heads, and the outside of the timber 

 becomes C(jatcd Avitli an impenetrable crust, so tliat the ]jrest'nce 

 of the nails is hardly necessary. — Journal of the Franklin Insii- 

 tute, Nov., 1866. 



METRICAL SYSTEM OF WEIGHTS AND MEASURES. 



The subject of a decimal system of measure resolves itself into 

 twojiarts, — the desirability of a decimal sjstem, and the standard 

 of measure to be adopted as the unit; the first of which may now 

 be considered settled, and the principle delinitel}^ adopted in tliis 

 country, the use of decimal measures being now legalized by a 

 recent act of Parliament. But the second part of the subject, the 

 standard of measure, is still o])en, and is of very great impor- 

 tance ; the consideration of it involves two preliminary scieutilic 

 questions, and two practical conditions to ])e fullilled. 



In i-esi^ect to the first scientific question, — as to the standard 

 that can be rei)laced best in case of Ix'ing lost, — tiiere is no rcjal 

 choice between the metre and the inch ; for the metre Iiaving I)een 

 originally detennined by measuring part of a quadrant of the 

 earth's circumference, its length was also referred to the seconds 

 pendulum for facility of repeating the measurement; and the 

 inch being obtaineil irom tlie seconds pendulum, both the metre 

 and the inch are thus verified by the same means: indeed, the 

 relation between them being once established, any means of 

 verification is equallj' availal)le for l)oth. In regard to tlie second 

 scientific question, — as to the standard that is most universal in 

 the character of its basis, — the supjiosed advantage of the metre, 

 as an even fraction of tlie quadrant, has been proved l^y the results 

 of mor(* accurate measurement to be a mistake, its actual length 

 being an uninen IVaction of the quadrant, just as tlie inch is an 

 uneven fraction of the pendulum ; and the length of the quadrant 

 itself being difl'erent in diilerent longitudes, there is therefore no 

 choice between the metre and the inch, in respect of universality 

 of its basis. The present legal standard of measure in this coun- 

 try is an individual metallic yard measure, independent of any 

 reference to another source ; and the metre is similarly a continu- 

 ation or copy of an original standard metre which is now known 

 to dilfer from the exact measure that it was intended to rei^resent 

 of the quadrant. There is no practical advantage, however, as 

 regards accuracy, in dependingupon copying for the preservation 

 of a standard ; for, by Mr. Whitworth's process of contact meas- 

 urement, the accuracy in copying lengths can now be carried as 

 far as one milliontii of an inch, which is a higher approximation 

 than can yet be attained in measuring the length of a j^endulum 

 or an arc of the earth's circumference. 



