DE. J. P. JOULE ON THE SUEFACE-CONDENSATION OE STEAM. 
151 
Metal. 
No. 
Eefrigerating water. 
Conductivity. 
Copper. 
23 
343-1 " 
202 - 28 '] 
24 
612-82 
335-65 
26 
592-3 
297-38 
27 
739-8 
342-5 
28 
767-16 
^640-25 
353-6 
^314-43 
30 
606-33 
332-85 
31 
797-34 
408-89 
32 
691-69 
256-3 
33 
611-69_, 
300-41 J 
T 
iron. 
84 
85 
556 1 
456-6 
506-3 
279-24 1 
264-16 _ 
i 271-7 
Lead. 
70 
417-82^ 
330-53'1 
72 
394-07 
252-19 
73 
75 
655-42 
624-07 
>590-24 
336-18 
127-19 
^ 270-7 
76 
656-07 
212-67 
77 
793-98 J 
365-43J 
The water spaces around the copper, iron, and lead tubes were respectively -06, -065, 
and -05 inch wide. By reducing all the mean results to the space ’06 and 640-25 lbs. 
of water by means of the formulae we have already deduced, we obtain for the conduct- 
ing power with the three tubes the numbers 314’4, 302*2, and 255-1 respectively. 
Taking into account the thickness of the metal, which was *06 in the copper, *069 in the 
iron, and *125 in the lead tube, we arrive at the conclusion that the resistance to con- 
duction through the metal itself is so small in comparison with the resistance at the 
bounding surface of the metal and through the adhering films of water (inside as well as 
outside of the steam-tube), as to be almost inappreciable. 
We have seen that the tendency of the water flowing between the tubes is to adhere 
to their sides, and that a head of water of considerable height is required in order to 
give the water sufficient velocity to remove the adhering film rapidly. It seemed pos- 
sible that part of the force due to the head might be employed for the purpose of 
agitating the water. I have not yet found an opportunity to construct an apparatus for 
this purpose, but it occurred to me that the same object might be attained by placing a 
wire bent into the form of a spiral between the tubes. By this means the water would 
be impelled in a spiral direction, which would contribute largely to the rapid intermix- 
ture of the particles of water as they advanced. Accordingly, in experiments 97, 98, and 
99, this arrangement was tried for the first time. The spiral (in these three experiments 
only) was half of it left-handed, and the other half right-handed, so that the rotatory 
motion produced by the first half was reversed in the second. Although the thickness 
of the wire which formed the spiral was only one-third of the width of the water space 
in which it was placed, the effect it produced was marked, as the following results 
testify : — 
y2 
