126 THE EFFECT OF WAVES UPON A TAFFRAIL LOG. 
be nearly doubled and at the speeds of 16.5, 12.35, 10.0 and 8.35 we should 
expect the variation to be nearly zero. 
Fig. 6 is drawn amplifying and minimizing the variations shown in 
Fig. 4 to correspond with the maxima and minima at the above figured 
speeds. 
Now suppose that the log did not have a uniform rate in still water, 
TABLE I. 
mL we : Wave height 
a VL G will be. a 
1.0 1.480 20.3 Maximum. 230 feet. 
1.5 1.205 16.5 Minimum. — 
2.0 1.025 14.05 Maximum. 110 feet. 
2.5 -904 12.35 Minimum. — 
3.0 .808 11.05 Maximum. 68 feet. 
3-5 -730 10.0 Minimum. : — 
4.0 .67 9.18 Maximum. 47 feet. 
4.5 -61 8.35 Minimum. _— 
5.0 -57 7.75 Maximum. 33 feet. 
which is usually the case, but that at slow speeds it had a greater error; then 
instead of the curve of Fig. 6 being plotted about a straight line A—B it 
would be plotted about the curved line A—B of Fig. 7, where A—B would 
represent the rate of the log in still water. This, then (Fig. 7) would give 
a curve that would show the variation in log factor for speeds from 8 knots 
Fic. 6. 
to 16 knots of a log towed 255 feet astern of the ship under discussion, pro- 
vided the log had a quiet-water calibration corresponding to A-—B, of Fig. 7. 
On the progressive speed trials of the U. S. R. C. Gresham (which had 
a length between perpendiculars=188 feet), the recording log previously 
described was towed 255 feet behind the stern post and the speeds over 
the course were taken by a recording chronograph (described in Professor 
C. H. Peabody’s paper read at this meeting) on which were recorded also 
the contacts made by the electric log every one-twentieth of a knot. The 
