288 PROFESSOR W. THOMSON ON THE DYNAMICAL THEORY OF HEAT. 
is, that the steam in rushing through the orifice produces mechanical effect which 
is immediately wasted in fluid friction, and, consequently reconverted into heat, 
so that the issuing steam at the atmospheric pressure would have to part with as 
much heat to convert it into water at the temperature 100° as it would have had 
to part with to have been condensed at the high pressure and then cooled down 
to 100°, which, for a pound of steam, initially saturated at the temperature ¢, is, 
by REGNAuLt’s modification of Wart’s law, °305 (¢— 100°) more heat than a pound 
of saturated steam at 100° would have to part with to reduce it to the same state ; 
and the issuing steam must, therefore, be above 100° in temperature, and dry. 

