148 
DE. J. P. JOULE ON THE SUEFACE-CONDENSATION OF STEA3I. 
Suppose we take the average index, then will express the influence of the 
quantity of refrigerating water on the conductivity with sufficient accuracy. But it is 
evident that this relation can only be relied on between certain limits, indicated prettv 
plainly by the experiments. The influence of a change in the quantity of refligerating 
water is doubtless gradually lessened as the flow is increased, and ultimately at a very 
high velocity the conductivity must necessarily reach a constant value. 
To find the influence of the extent of the water space, successively narrowed by dimi- 
nishing the diameter of the outside tube, we will select those experiments in which the 
flow of water was nearly the same in quantity. 
Width of water space 
between the tubes. 
No. 
Quantity of refrigerating 
water. 
Conductivity. 
0-325 inch. 
5 
591-on 
152-24d 
6 
631-85 1 
184-3 
7 
594-47 >614-46 
149-44 
>155-27 
8 
597-01 1 
138-79 
9 
657-99 J 
151-6 J 
0-06 inch. 
24 
612-821 
335-65^ 
26 
592-3 
297-38 
30 
606-33 
>622-96 
332-85 
>304-52 
32 
691-67 
256-3 
33 
611-69 J 
300-41 J 
0-025 inch. 
48 
523-12^ 
473-3 
49 
511-08 
490-99 
50 
533-23 
498-64 
51 
572-52 
512-66 
52 
621-95 
>554-22 
370-49 
>488-34 
57 
504-77 
334-13 
59 
545-47 
589-21 
60 
589-14 
564-26 
61 
586-75_^ 
56l-39_, 
Eeducing the conductivity in each C8.se to the flow of 618 lbs. of water, by the rule 
just found, we deduce for the spaces ’325, ‘06, and ‘025, the conductivities 156, 303'7, 
and 504-4 respectively. Whence, for the circumstances of the experiments, it follows 
that 1 
CocS^■‘^^ 
The above laws are neither exact, nor universal in their application, but they afford 
the means of estimating the probable amount of benefit to be anticipated from increasing 
the rapidity of the refrigerating stream in such tubes as I have employed, which are 
indeed of the dimensions most likely to be practically adopted. 
1 pass now to the consideration of the effect of cleanliness of surface. In the experi- 
ments 62, 63, and 64, the outside of the copper steam-tube was made greasy by rubbing 
it -unth oil. In the five immediately preceding these the tube was kept perfectly clean, 
so that water readily adhered to it. 
