322 



The November pulse has a duration of 21 days, — from Nov. 

 2 to 23, — with a maximum amplitude of 1.86 cm. 3 per m. 3 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 (PI. 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 

 at a fair volume for this time of the year throughout the last 

 half of the month, bringing the monthly average up to 1. cm. 3 

 per m. 3 — an amount surpassed only by the heavy production of 

 1895 (3.02 cm. 3 See table on p. 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. 3 per m. 3 

 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 l.l 

 ft. The ice-sheet covered the river during most of the month 

 (PI. XI.), 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 (PI. XLIV.). The free am- 



