Porta, on the Reflection of , Cold &c. 1 69 



smallest, limbcrest, and least subject to retch : let this ball 

 be suspended by this string, being extended to such a length, 

 that the space of every vibration may be equal to a second 

 minute of time, the siring being, by frequent trials, either 

 lengthened or shortened, till it attain to this equality : these 

 vibrations should be the smallest, that can last a sufficient 

 space of time, to afford a considerable number of them, 

 cither 6 or 500 at least; for which end, its passing an arch 

 of five or six decrees, at the first, may be sufficient. The 

 pendulum being so ordered as to have every one of its vi- 

 brations equal to a second minute of time, which is to be 

 adjusted with much care and exactness ; then measure the 

 length of this string from its place of suspension to the 

 centre of the ball ; which measure must be taken as it hangs 

 free in its perpendicular posture, and not otherwise, because 

 of stretching : which being done, there are given these two 

 lengths, viz. of the string, and of the radius of the ball, to 

 which a third proportional must be f(juud out ; which must 

 be, as the length of tlie string from tlie point of suspension 

 to the centre of the ball, is to the radius of the ball, so must 

 the said radius be to this third : which being so found, let 

 two-fifths of this third proportional be set off from the 

 centre downwards, and that will give the measure desired. 

 And this (according to the discovery and observation of 

 those two excellent persons, the Lord Viscount Brouncker, 

 President of the Royal Society, and M. Hm/gens, a worthy 

 member of it) will prove to be 38 Rhinland inches, or, 

 which is all one, 39 inches and a (quarter, according to our 

 London standard. 



*' Let this k'/igf/i therefore be called the standard ; let 

 one tenth of it be called a foot; one tenth of a foot, an 

 inch; one tenth of an inch, a line. And so upward, tea 

 standards should be a jjcrcb ; ten perches a furlong ; ten 

 hirlongs a mile; ten miles a league, &c. 



" And so for measures o\i ccifjuclty : the cubical content 

 of this standard may be called the bushel ; the tenth part of 

 the bushel, the peck; the tenth part of a peck, a quart ; 

 and the tenth of that, a pint, he. And so for as n)any 

 other measures upwards as shall be thought expedient for 

 use, 



" As for measures of trrinh/ ; let this cubical content of 

 distilled rain wafer be the hundred; the tenth part of that, 

 a stone ; the tenth part of a stone, a pound ; the tentli part 

 i»t a pound, an ounce ; the tenth of an ounce, a dram ; the 

 Itnth of a dram, a scruple ; the tenth of a scruple, a grain, 

 &.O. And so upwards; ten of these cubical measures may 

 2 be 



