134 Le Roy's Memoir on the best Method 
After being well assured of the fact I have just described, 
it appeared necessary to examine a second, not less impor- 
tant to clear up, and to know whether metals would follow 
the same progression as fiuids/in their extension or contrac- 
tion by heat and cold; which required very nice experig 
ments. To make them with some success, I nailed in a 
cabinet against.a thick stone wall, at four feet distance from 
each other, in a vertical line, two potences of copper, the 
upper one of which carried an index of thin hard steel 
about four feet in length, which descended almost vertically : 
T then took three rods, one of copper, one of iron, and one 
of steel, of nearly equal size, and four fect in length. Thad 
made to each of these rods, ‘as well as to a tube of glass of 
exactly the same length, to serve as a standard, a sheath, 
made sufficiently thick of cloth: these rods and this tube 
were adjusted firmly, without being able to turn, by their 
lower extremity, and by a, pivot adapted to their upper 
extremity, they caused the index to move whose path was 
marked on a limb. 
- All being equal in the arrangement of the three rods and 
the tube, I began my experiments, and I presently saw that, 
to have any thing exact on this subject, it was necessary that 
- the rods should remain a Jong time exposed to the degree of 
heat and cold in which we would make these experiments 5 
particularly when from a considerable degree of heat, as 20 
or 30 degrees * for example, I wished to remove my rods to 
a degree of cold approaching that of ice. The reason is 
known: by the experiments of Boerhaave, and those of 
Newton, bodies attract heat in proportion to their specific 
gravities. Now when you would remove a body whose de- 
gree of cold corresponds to 6 of the thermometer, for ex- 
ample, to the term 30 degrees of this same instrument, by 
placing it in an air that is "Be this degree, it is clear that by 
its attraction it will presently have acquired the quantity of 
caloric that will give it the degrce of heat 30. But it will 
not be the same if you then remove this body to an air where 
the thermometer is OF, to make it acquire this degree of colds 
* Of Reaumur’s thermometer, equal to from 77 to 99% of Fahrenheit’s. 
+ $2 of Fahrexheit. 
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