A16 Scientific Intelligence. 
lionths of a meter, or the relation between a meter and a quarter of ar 
terrestrial meridian. This screw turns between two points x, screwed 
into the slide which supports the contact lever, and is situated in the 
same line with the points of contact. 
The delicacy of the points of contact being ascertained, there is es 
a condition to be provided for, viz.: the invariability of the distan 
tween the two heel-points of the ae ers, an invariability ee 
disturbed by variations of temperatu 
To insure an invariable length in = bronze rule, which serves as a 
support to the levers, M. Silbermann applies to this rule, the rule aad 
of platinum, which, as the dilatation of the two metals is very different, 
makes of the couple a thermometer of Borda (fig. 2); and it indicates 
for each instant, the temperature of the system. This is the object of 
uniting the two rules at one end c, by a pin which goes through both, 
while at the other end, they are free. The difference of dilatation is 
indicated by a scale c, divided into fourths of millimeters, traced upon 
the platinum rule. A vernier made of a plate of platinum is fixed 
against the bronze rule, which divides 24 of these fourths into 25 parts, 
and indicates thus hundredths of a millimeter. This plate serves also” 
to guide the platinum rule, while the foot of the nut of the micrometric 
screw guides the rule on the other side. 
For og aan the sovoments of dilatation of aus thermometer of 
2, the le ever d” f” e”, (fig. 2) is introduced. The arc e’ which ter- 
tes the arm of the’ lever, f” e”, carriers a vernier which moves 
Pp si a divided arc, m’, whose foot carries the axis f”, of the lever 
fixed to the bronze rule b 3’. The divisions of the vernier register 
50ths of a degree of temperature. 
This apparatus for the comparisons (‘‘ comparateur”) rests on sev- 
eral pieces, y, of equal thickness, and these on a support of brass, ac- 
curately plane 
“he following i is briefly the method of using ons me plese in com: — 
paring a meter under trial with the prototype stan 
The standard is put upon the Borda <i bia (ig 2); the whole 
in ice; by means of 1, its extremity is put into coincidence © 
with d', so that the two zero marks e! m’, are coincident; then by 
means of the screw ¢, the slide ghi, is moved until the extremity d of 
the small arm of the lever touches this extremity of the standard meter, 
80 as to bring into coincidence the two zero marks. : 
This same operation is performed with the meter under trial and the 
ae is noted on v. This reading is quite correct, only whea the 
7 ometer indicates that the temperature has not varied. 
“Standard Meter.—The standard meter is made of annealed 
Ee nitiee of these two rules carry each a 
the bronze rule is cut on a silver plate, ve 
The vernier is fixed: upon the stee 
measu meter may be used for comparison with meters which: 
= meter rade between the cxtttediitns: or. onto a 
the surface. In the former ¢ meter is inserted between 
