are to be found in the sluices of valves for water?

_A._--Various experiments have been made by Mr. Summers of Southampton to
ascertain the friction of brass surfaces sliding upon each other in salt
water, with the view of finding the power required for moving sluice doors
for lock gates and for other similar purposes. The surfaces were planed as
true and smooth as the planing machine would make them, but were _not_
filed or scraped, and the result was as follows:

Area of Slide Weight or Pressure on Power required to move the
rubbing rubbing Surface. Slide _slowly_ in muddy
Surface. Salt Water, kept stirred up.

Sq. in. Lb. Lb.
8 56 21.5
" 112 44.
" 168 65.5
" 224 88.5
" 336 140.5
" 448 170.75

[Illustration: Fig. 2. Sketch of Slide. The facing on which the slide moved
was similar, but three or four times as long.]

These results were the average of eight fair trials; in each case, the
sliding surfaces were totally immersed in muddy salt water, and although
the apparatus used for drawing the slide along was not very delicately
fitted up, the power required may be considered as a sufficient
approximation for practical purposes.