DISCUSSION OF TIDES IN BOSTON HARBOR. 47 
our tidal expressions based: upon the dynamic theory have been pointed out. These are due, no 
doubt, mostly to friction in connection with ocean currents, and to the peculiarities arising from 
local circumstances, which cause many small terms, which are necessarily neglected in the tidal 
expressions, and which in most ports are insensible, to be quite large in the Boston tides. 
Much study and care has also been given to the formation, from these results, of the most 
convenient formule possible for the prediction of the times and heights of the tides, and by means 
of various auxiliary tables, to render the labor of their computation as small as possible. An 
example has also been given of the most convenient method of carrying out the computations, from 
which it may be seen that they can be made with great facility and also with great accuracy. 
In the comparison of individual tides as computed with the formule and tables, with obser- 
vation, considerable discrepancies are often found in both the times and: the heights, as is to be 
expected, on account of the many abnormal disturbances arising from the changes in the forces and 
directions of the wind and in the barometric pressure, and these discrepancies are especially found 
during the winter and spring, when these changes are the greatest; but still it is thought that the 
computation gives very accurately the true normal tide. From the discussion of these residuals 
with reference to the winds and the barometric pressure, some interesting results may yet be 
obtained with regard to their effects upon the tides. The computation of the tides for a portion of 
the series is now being made for this purpose, the results of which must be the subject of a future 
report. 
In the prosecution of the preceding discussions I have to acknowledge the receipt of much 
valuable and very satisfactory aid from the Misses Lane, in the Coast Survey service. 
Very respectfully, yours, 
WM. FERREL. 
Professor BENJAMIN PEIRCE, 
Les Superintendent United States Coast Survey. 
Nore.—The following tables are added by way of appendix to the preceding discussion of the Boston tides. They 
were prepared by Mr. Ferrel, and show the application of the theory. 
