250 REPORT—1874, 
ones, the calico. But in each case pains were taken to secure uniformity, 
and no difference of perceptible amount was permitted. 
A tolerably correct perception of the different degrees of roughness ob- 
tained with the roughened surfaces will be conveyed by the full-size photo- 
graphic representations (Plate XIT.). 
In forming all the surfaces care was taken to avoid abnormal roughness, 
and to eliminate the effect of thickness of cutwater and of stern-end or run, 
the ends of all planes being formed as shown in plate 3 of the previous 
Report. In the case of the calico, a fine entrance was obtained by placing a 
sharp tin cutwater, 1 inch long, over the seam at the front edge of the 
plane; the calico was also carefully closed round the tail, and a fairly fine 
run secured. 
The results obtained are shown in full detail in the accompanying dia- 
grams, four in number, which, as in the former Report, represent them 
seriatim, as finally reduced, in two separate forms. In one form (series 1, 
Plates VIII. & IX.) the abscissee or measurements along the base line repre- 
sent speed; in the other (series 2, Plates X. & XI.) they represent length of 
surface. The corresponding ordinates in each case represent resistance. 
In the first-named series, each of the successive lengths of surface has a 
group of curves assigned to it, corresponding with the various qualities of 
surfaces, and exhibiting the law of resistance in terms of speed of surface. 
In the second-named series, each of the successive speeds of surface has a 
group of curves assigned to it, corresponding with the various qualities of 
surface, and exhibiting the law of resistance in terms of length of surface. In 
each of the diagrams, curves showing the results given by a surface coated 
with shellac varnish are given as a standard of comparison, the former ex- 
periments having shown that this quality of surface might be regarded as in 
some sense a standard quality—it being easily laid on with invariable 
quality, and being practically identical in respect of resistance with Hay’s or 
Peacock’s composition, smooth paint, or tallow. These standard curves are 
copied from the diagrams which accompanied the former Report. 
The planes used in the experiments were, as before, about 19 inches wide ; 
but the resistances shown for each length are those of the entire length of 
surface, assuming it to be of parallel width, and to expose to the frictional 
action one square foot of surface per foot of length. 
Tt will be seen that the diagrams of each form are deducible from those of 
the other, 
The results are shown in a more compendious but necessarily less complete 
form in the accompanying tabular statement (p. 251). 
This represents the resistances per square foot due to various lengths of 
surface, of various qualities, when moving with a standard speed of 600 feet 
per minute, accompanied by figures, in smaller type, denoting the power of 
the speed to which the resistances, if calculated for other speeds, must be 
taken as approximately proportional. 
Under the figure denoting the length of surface in each case, are three 
columns, A, B, C, which are referenced as follows :— 
A, Power of speed to which resistance is approximately proportional. 
B. Resistance in pounds per square foot of a surface the length of 
which is that specified in the heading—taken as the mean resist- 
ance for the whole length. 
C. Resistance per square foot on unit of surface, at the distance 
sternward from the cutwater specified in the heading, 
