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THE EFFECT OF WAVES UPON A TAFFRAIL LOG. 133 
if the line of advance of the sea forms an angle @ with the course of the ship, pro- 
vided the speed of the waves is (Sec. 6) times the speed of the ship, and provided 6 
is smaller than 90 degrees. When the sea is forward of the beam, no permanent 
influence on the log seems possible, since the waves will in that case always 
be passing. 
In reality the waves of the sea are irregular, and their speed will rarely conform 
exactly to the above rule. We may, therefore, expect that this source of error will 
be negligble in general, but cases may arise where it ought to be taken into account. 
Mr. CHARLES P. WETHERBEE, Member:—I wish to say it seems to me as if there 
might be some other factors also, that affect the accuracy of the log, such as the wake 
of the propeller and the immersion of the log. Of course the immersion depends on 
its distance from the vessel. As near as I can understand from Professor Everett’s 
paper his conclusion is that the log is unreliable, but that it can be standardized, 
so that no matter what the errors depend upon they can be taken into account in 
the standardization. 
The general opinion among seagoing people seems to be that the revolutions of 
the screws are really a more accurate gauge of the speed of a ship than the log, and 
while the revolutions of the screws vary under different weather conditions, they do 
not vary as much as the variation of the log. 
VICE-PRESIDENT McFarLanp:—Apparently there is no further discussion on 
this paper. As there has been no criticism, do you care to say anything further, 
Professor Everett? 
PROFESSOR EVERETT:—With reference to Professor Hovgaard’s remarks, I 
think that is an interesting point which he brought out, but, of course, it applies 
to only one condition which occurs, and that but rarely, that is, when the waves of 
the sea are of the same identical speed as the waves of the ship. 
With regard to Mr. Wetherbee’s point, the race may affect the log, but it is 
impossible to separate it, and it would seem to be in the nature of a constant variant. 
The depth of immersion must have an influence on the amount the log overruns or 
underruns, but at the same time I have said in my paper that the log must be cali- 
brated under the identical conditions under which it is to be used, and if the condi- 
tions with reference to length of log line and speed are the same, the chances are the 
log immersion is the same, so that the question of depth of immersion is taken care of 
in the calibration plot. I am not advocating the calibration plot for the log, to 
permit it being used as an accurate measurer of speed or distance, because I question 
if it could be derived to the accuracy desired, but my principal point is that the log 
is very unreliable unless calibrated as outlined. 
VICE-PRESIDENT McFar_LaNnD:—With which we all agree. 
We extend the thanks of the Society to Professor Everett for his interesting 
