MAEASURE. 
circular arc of 3“ 20', is verj' nearly 39.119 ; 
but performing the same motion in the 
arc of a cycloid, the result would be 39.136 
inches; consequently, weighty substances/ 
will descend in the first second after they 
are detached from their support nearly 
16.094 feet, or 16.11 inch. 
Dr. Young, to whom we acknowledge 
ourselves indebted for many of the follow- 
ing particulars, has given an excellent com- 
pressed table of measures and standards, in 
his recent valuable work, “ A Course of 
Lectures on Natural Philosophy,” &c. from 
which we find, that the English yard is said 
to have been derived from the length of the 
arm of Henry I. in theyearllOl; thatGra- 
ham asserts the length of the pendulum vi- 
brating seconds accurately is equal to 39. 13 
inches; that Bird’s parliamentary standard is 
admitted to be of the greatest authority, 
and that it agrees nearly with the scales of 
Shuckburgh and Pictet, made by Trough- 
ton. The standard of the Royal Society by 
Graham exceeds that of Bird’s in length 
about 1000th part of an inch, but it is not 
quite uniform throughout its length. The stan- 
dard in the Exchequer is about .0075 inch 
shorter tlian the yard of the Royal Society. 
General Roy used a scale of Sisson, divided 
by Bird, and found it to agree exactly with 
the Tower standard on the Royal Society’s 
scale. Sir George Shuckburgh, adopting 
Troughton’s scales for the standard, found 
the original Tower standard 36.004 ; the 
yard E. on the Royal Society’s scale by 
Graham 36.00 J 3 inches ; the yard Exche- 
quer of the same scale 35.9933 ; Roy’s 
scale 36.00036 ; the Royal Society’s scale 
by Bird 35.99955 ; Bird’s parliamentary 
standard of 1758, 36.00023. The English 
have employed and adjusted their standards 
at the temperature of 62° of Fahrenheit's 
thennometer, and the French at the freez- 
ing point of water. The French metre is 
39.37100 IJnglish inches, and the teu mil- 
lionth part of the quadrant of the meridiitn. 
The same measure contains 36.9413 French 
inches, or Sfeet 11.296 lines. Hence, says the 
Doctor, the French toise of 72 inches is equal 
to 76.736 English inches. One of Lalande’s 
standards measured by Dr. Maskelyne was 
76.732, the other 76.736. In latitude 45°, 
a pendulum of the length of a metre would 
perform in a vacuum 86116.5 vibrations in 
a day. The length of the second pendulum 
is 993827 at Paris. 
The French National Institute of Sciences 
and Arts have turned their attention to this 
subject, and in the month of Nivose, in the 
year 1801, a member read a report from a 
committee, founded on the comparison of 
the standard metre of the Institute with the 
English foot. And M. Pictet, professor of 
natural philosophy at Geneva, exhibited to 
the class, in the month of Vendemiaire, a 
collection of the most interesting objects, 
which he had collected in England, relating 
to arts and sciences. One of the number 
was, a standard of the English linear mea- 
sure, which was of brass, 49 inches in 
length, and neatly divided by engi aved lines 
into tenths of an inch. This standard was 
made for the exhibitor by Troughton, a rest- 
- dent in London, who has deservedly ac- 
quired the reputation of dividing instru- 
ments with the utmost accuracy, which was 
compared with another made by the same 
artist for Sir George Shuckburgh, when it 
was ascertained satisfactorily, that the va- 
riations betw'een them did not amount to 
more than the difi’erence between the divi- 
sions of each ; in other words, the variation 
was almost imperceptible. Arguing from 
this circumstance, the standard may be con- 
sidered as identical with that described by 
Sir George Shuckburgh in tlie Philosophi- 
cal Transactions for 1798. 
Another excellent instrnraent, construct- 
ed by Mr. Troughton, and shewn at the 
same time by M. Pictet, was a comparer, 
calculated to ascertain minute variations 
between measures. 'Fliis instrument “ con- 
sists of two microscopes, with cross wires, 
placed in a vertical situation, the surface of 
the scale being horizontal, and fixed at 
proper distances upon a metallic rod. One 
of Them remains stationary at one end of 
the scale, the other is occasionally fixed 
near to the other end ; and its cross wires 
are moveable by means of a sci ew, describ- 
ing in its revolution ^tli of an inch, and 
furnished with a circular index, dividing 
each turn into 100 pafts; so that having 
two lengths, which differ only one-tenth of 
an inch from each other, we may determine 
their difference in ten-thousand tlis of an 
inch. The wires are placed obliquely with 
respect to the scale, so tliat the line of divi- 
sion must bisect the acute angle wliich they 
form, in order to coincide with tlieir inter- 
section.” An instrument similar to that 
thus described, and made by Ramsden, for 
measuring the expansion of metals, was de- 
scribed by General Roy in the seventy-fifth 
volume of the Royal Transactions. 
M. Pictet, influenced by a desire of ad- 
vancing science, made an offer to tlie class 
the use of the standard and the micrometef 
