322 
The November pulse has a duration of 21 days,—from Nov. 
2 to 23,—with a maximum amplitude of 1.86 cm.* per m.* on 
the 15th. Its mean falls on the 16th, 42 days after that of the 
preceding pulse. The limit between this and the December 
pulse is not well defined in the volumetric data, and any treat- 
ment from the cyclic standpoint seems arbitrary. The end of 
the pulse might as well be regarded as Dec. 7, in which case its 
duration is 35 days and its mean falls on the 21st, 47 days after 
the preceding one. The conditions during this month are not 
so stable as during September and October. The autumn rains, 
though slight, cause a movement in levels of 2.1 ft. and intro- 
duce considerable silt into the stream. These are insufficient 
to flush out the river or to materially reduce the sewage con- 
tamination. ‘There is some decline in chlorine (Pl. XLIV.) and 
considerable in nitrites, but the free ammonia continues to rise 
rapidly, indicating much organic material in process of decay. 
The nitrates also show much increase. The temperature de- 
cline to the winter minimum is completed. The production 
rises, however, in these conditions from .06 to 1.86, and continues 
ata fair volume for this time of the year throughout the last 
half of the month, bringing the monthly average up to 1. cm. 
per m.*—an amount surpassed only by the heavy production of 
1895 (5.02 em.* Seetable onp. 292). This is also a year of sta- 
ble November hydrograph. It may be noted that the maximum 
accompanies a pulse of nitrates and a check in the falling tem- 
perature , and that the decline on Dec. 7 attends a drop to the 
minimum beneath the forming ice. 
The December pulse has a duration of 21 days,—from the 
7th to the 28th,—with its greatest amplitude of 1.22 cm.’ per m2 
on the 14th, and its mean on the 16th—30 (25) days after that 
of the preceding one. This is likewise a month of stable hydro- 
graphic conditions, the total movement in levels being only 1.1 
ft. The ice-sheet covered the river during most of the month 
(Pl. XL), with a slight break with rising levels in the second 
week. This closing of the river conduced to stagnation, as is 
shown by the chemical conditions (Pl. XLIV.). The free am- 
