As to the observed point of low water, it is to be noted that during the whole period of observation, water was flowing from Spy and Little Ponds through their natural outlets, most of the time escaping by Alewife Brook to Mystic River, but, during a short period, being constrained by a dam to flow back into Fresh Pond. The minimum point to which those ponds would fall was obviously controlled by the condition of their outlets, both of which are much obstructed by stones and other foreign matters. I feel, therefore, obliged to report that it has not been practicable to "ascertain" the lowest point to which these ponds might flow.

I have caused stone monuments to be set at Spy and Little Ponds, indicating high water mark. Also a mark cut into the granite facing of the gate to the well of the City Water Works at the Engine House on Fresh Pond, indicates high water. These will be sufficiently permanent for reference, and the low water points may at any time, when definitely settled, be determined by measurement.

I have only to add that continuous observation to this date has not shown any greater height of water than that indicated before.

I have the honor to subscribe myself, with the greatest respect, Your Excellency's obedient servant,

ESTES HOWE.

HON. ESTES HOWE:-
:-

OFFICE OF CITY ENGINEER,
CAMBRIDGE, September 25, 1871..

DEAR SIR,-Directed by you, in the performance of your duties as Commissioner under the Statute of 1856, chap. 290, to ascertain the relative heights and fluctuations of Fresh Pond, Spy Pond, and Little Pond, I have the honor to report: —

Gauges have been established at the three ponds, having a cominon base which is twenty feet below the coping of the dry dock at Charlestown, and 5.26 feet below mean low water. The heights of water above this base, shown by the readings of the several gauges, have been observed daily for one year, from

April 13, 1870, to April 12, 1871, inclusive, these heights being given in the tables which accompany this report. During the month of October, 1870, additional observations were made, to determine the times and heights of high water at Alewife Brook, where North Avenue crosses the same, and at the outlet of Fresh Pond, the gate being closed to prevent water flowing to or from the pond. A comparison of these data with similar records obtained from the Coast Survey Office of times and heights of tides in Boston Harbor, is also given. And I have prepared a diagram which represents very clearly to the eye the changes and comparative heights of the ponds throughout the year of observation, upon which may be drawn the points settled upon for established heights of high and low water, should they be so determined by you, under the powers conferred upon the Commis

sioner named in the act referred to.

From an examination of the gauge records, it appears that the highest point reached by water in Fresh Pond was 16.85 on April 21st-22d, 1870. Water in Little Pond on the 21st was .48 below Fresh Pond, and on the 22d .50 lower. Water in Spy Pond was .30 lower than Fresh Pond on the 21st, and .25 lower on the 22d.

Highest water in Spy Pond occurred on April 22d, 1870, being at 16.60.

Highest water in Little Pond occurred February 21st, 1871, being 16.50, at which time the water was .70 lower in Spy Pond and 3.45 feet lower in Fresh Pond.

Lowest point reached in Fresh Pond, 12.44, occurred on the 22d of November, 1870, at which time the water was 2.86 feet higher in Spy Pond, and 1.94 feet higher in Little Pond.

Lowest water in Spy Pond, 15.14, Sept. 23d, 24th, and 25th. Lowest water in Little Pond, 14.40, Nov. 18th, 21st.

Difference between highest and lowest water in Fresh Pond, 4.41 feet; highest and lowest of Spy Pond, 1.46 feet; highest and lowest of Little Pond, 2.10 feet.

Greatest difference between Fresh and Spy Ponds occurred on the 22d of November, 1870, being 2.86 feet. On the 25th of April, 1870, Fresh Pond was .15 higher than Spy Pond. The nearest approach to the same level again occurred on the 2d of April, 1871, when Fresh Pond was .59 lower than Spy Pond.

Average of the year for Fresh Pond, 14.02. Average of the year for Spy Pond, 15.64. Average of the year for Little Pond, 15.16.

By the observations alluded to, it is shown that, during the month of October, the water in Alewife Brook was constantly above the water in Fresh Pond. The greatest difference was 2.04 feet on Oct. 27th. Without the gate as maintained, a constant stream of deleterious waters would have been received into the pond, putrid from the marshes and accumulations in the stagnant channel of Alewife Brook, as well as salt water thrown back by the tides. A reference to the tide table will also show that the lowest observed tide at outlet of pond during the month of October was higher than the monthly average of the pond from August to February inclusive. That such a gate of separation should be permanently maintained at this point in the brook, to preserve the water supply of Cambridge from needless contamination, is sufficiently evident.

I have also, as directed, set permanent stone monuments at Spy and Little Ponds. The one at Spy Pond is near its outlet to Little Pond, its top indicating extreme high water observed there, and the one at Little Pond being about midway upon its southerly shore, and placed to indicate extreme height of water as observed in said Pond. At Fresh Pond, I have fixed permanently a copper bolt into the northwest granite column of screen room at the Pumping Works, the top of which is placed at the point of extreme high water observed there.

Very respectfully submitted,

J. G. CHASE.