produced, with the assistance of Mr. Dancer, instrument maker, of
Manchester, the first English thermometers possessing such accuracy
as the mercury-in-glass thermometer is capable of. Some of them were
forwarded to Prof. Graham and to Prof. Lyon Playfair; and the production
of these instruments was in itself a most important contribution to
scientific equipment.

As the direct experiment of friction of a fluid is dependent on no
hypothesis, and appears to be wholly unexceptionable, it was used by Mr.
Joule repeatedly in modified forms. The stirring of mercury, of oil,
and of water with a paddle, which was turned by a falling weight,
was compared, and solid friction, the friction of iron on iron under
mercury, was tried; but the simple stirring of water seemed preferable
to any, and was employed in all his later determinations.

In 1847 Mr. Joule was married to Amelia, daughter of Mr. John Grimes,
Comptroller of Customs, Liverpool. His wife died early (1854), leaving
him one son and one daughter.

The meeting of the British Association at Oxford, in this year, proved
an interesting and important one. Here Joule read a fresh paper "On the
Mechanical Equivalent of Heat." Of this meeting Sir William Thomson
writes as follows to the author of this notice:

"I made Joule's acquaintance at the Oxford meeting, and it quickly
ripened into a lifelong friendship.

"I heard his paper read in the section, and felt strongly impelled at
first to rise and say that it must be wrong, because the true mechanical
value of heat given, suppose in warm water, must, for small differences