256 REPORT—1874. 
(1) If a plane be moving edgeways 
through the water, and the end of a pipe 
connected with a _ pressure-gauge be 
brought square through the plane and 
terminates flush with the surface (fig. 1), 
the motion of the plane causes a small 
positive pressure within the pipe, amount- SC 
ing to about :04 of the pressure due to 
the speed. If, however, the end of the 
pipe be not very exactly flush with the 
plane, this positive pressure is increased 
when the rearward edge is the projecting 
part (fig. 2), and is diminished, or even 
becomes negative, when the position is 
reversed (fig. 3). If the end of the pipe 
is flush with the plane, but has its in- 
ternal edge slightly rounded off (fig. 4), 
the positive pressure caused by motion of 
the plane very nearly disappears. 
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If the end of the pipe be closed by a | Fig.3 
disk forming a smooth fiush end with a Ef 
small aperture in it (fig. 5), there is no ————__}___}... a 
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appreciable positive pressure caused by 
the motion of the plane; nor is positive or ssssss 
negative pressure caused when this disk 
forms a slight angle with the line of 
motion, whether facing forward or facing 
sternward (figs. 6 & 7), unless the angle 
is considerable (say some five degrees or 
80), a very much larger angle than pro- 
duced considerable effect of this kind with 
the open-mouthed pipe. , 
The pipe with which these results were 2 
Line of Motion re 
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IN NSANLT SASS SSS 
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obtained was about 4 inch diameter, and 
the speeds used ranged from 280 to 600 
feet per minute. 
(2) In acylindrical tube projecting into 
the fluid at right angles to the line of SGGSSSS% 
motion, with the end closed but with a 
hole in the side, the angle of position of 
the neutral point, referred (that is to say, 
measured circumferentially from the fore- 
most side of the cylinder) to the point 
where the pressure is not affected by the 
motion, depends considerably upon the 
relative diameter of the tube and the hole 
in it. The greater the relative diameter 
of the hole, the greater is the angle of 
position of the neutral point. Thus the 
angle of position of the neutral point in a 
tube 1:1 inch external diameter, having 
a z)-inch diameter hole, seems about 
40°°5; that of the same tube with a hole GW] FFARR 
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