154 
DE. J. P. JOULE ON THE SUEFACE-CONDENSATION OE STEA3I. 
therefore be 500’7 and ^ 45 . 49 ^ ^ X 684'89 = 554-06. The difference between the two 
values is not great. If we average them with the results obtained when the tubes were 
not furnished with spirals, we shall obtain the following result : — 
Tubes employed. 
Conductivity. 
Water going in 
the same direction. 
Conductivity. 
Water going oppo- 
site to the steam. 
Eatio of 
conductivities. 
Plain 
369-13 
350 
0-9482 
Furnished with spirals. 
500-7 
554-06 
1-1065 
Mean 
1-0273 
showing a trifling advantage on the side of the arrangement in which the refrigeratuig 
water goes in a contrary direction to the steam and condensed water, which is, however, 
too small to be attributed to anything beyond experimental errors. 
The quantity of transmitted water being, cceteris paribus, nearly proportional to the 
square root of the height of the head, it is evident that the limit to the economical 
increase of the conductivity by diminishing the thickness of the water space, or by 
increasing the velocity of the stream, is soon attained. Hence, as I have already 
observed, the importance of any method which promotes the rapid removal of the adhe- 
ring film of water without necessitating a great initial pressure. I have arranged my 
results, with reference to the head of water in the following Tables, so as to enable a 
comparison to be readily made in this respect between the plain tubes and those 
furnished with spirals. 
Table I. — Plain Tubes. 
Description. 
No. 
Head of water. 
Conductivity. 
Copper steam-tube 4 feet long. 
2 
— O-15'l 
158-46'^ 
Thickness of water space 0-325 inch. 
1 
0-2 
98-13 
5 
0*47 
152-24 
8 
0-47 
138-79 
7 
0-52 
;>0-56 
149-44 
;>157-83 j 
9 
0-54 
151-6 
1 
6 
0-66 
184-3 
3 
1-13 
195-68 
4 
1-2 J 
19 1*86 J 
Copper steam-tube 4 feet long. 
18 
- 1-4 1 
89-62“] 
Thickness of water space 0-06 inch. 
21 
- 0-49 
279-85 
19 
20 
— 0-13 
0-6 
>0-69 
143-92 
155-91 
>176-92 
22 
1-19 
198-48 
17 
4-37 
193-77 
23 
6-45^ 
202*28"] 
90 
10-8 
278-07 
33 
11-48 
300-41 
30 
12-9 
f>12-08 
332-85 
S286-13 
24 
14-07 
335-65 
32 
14-15 
256-3 
26 
14-73J 
297-38 J 
