Within certain average limits these constituents remained unchanged, and oscillated between certain higher and lower levels in the soil, under the influence of evaporation on the one hand, and alternating accessions of rain water on the other.

But when occasion required the drawing down of the water considerably below the mean level, the water of the surrounding soil, with whatever it held in solution, naturally flowed into the lake. Every oscillation of level repeated this process.

The wants of the city of Boston have repeatedly provided this occasion for an influx of saline matter into the pond.

The accession of the water of Sudbury river for a time seemed to increase the foreign matter. But I am disposed to look upon the present analysis as giving an exceptional result, and that the substantial purity of the water for all time is assured. A year ago the water was nearly as pure as it was in 1845, as the following figures show: —

Total residue in 1845

❝ 1872.

1.85 grains.
2.06 66

The present level of Fresh pond is much below - several feet below its natural outlet, and it seems possible that the same phenomenon as that occurring at Lake Cochituate is being repeated in this sheet of water, with the probability that the water displaced by rainfalls from the surrounding marshes contains more saline matter to be forced into the pond. The stratum of salt water below, brought in by high tides in times long gone by, is doubtless diffusing itself with a relatively increased rapidity as the outflow of surface water over the dam is cut off.

The increase in the amount of inorganic matters in the Schuylkill finds explanation in the increased cultivation of the land on the shores of the tributaries, and in the burning of wood to

ashes in clearing new land from 1842 to 1854, and, perhaps, to the sulphur of the iron pyrites brought to the surface in the coal, and oxidizing spontaneously or burned in the manufacturing industries.

In more recent times, the increase of manufactures in the towns on and near the banks of the river and its tributaries have appreciably lessened the purity of the water. But I have at hand no recent analysis of the water to enable me to judge. The opinion of Booth and Boye, of Philadelphia, after a careful analysis of the Schuylkill water, following an interval of twelve years, in 1854, is that the development of manufactures on the tributaries to the Schuylkill had not in that time deteriorated the water in the quantity of organic matter in the slightest degree, though the inorganic matter had been slightly increased. In the judgment of these gentlemen the water had "deteriorated in no important respect from its former excellent quality."

The Croton reservoirs have been recently enormously enlarged, introducing large volumes of water from more interior drainage, so that the comparison of earlier and later analyses has no particular significance in its bearing upon the point in consideration.

The low marginal territory of the Upper Mystic is less extensive than that of Fresh pond, and the occasions of its being drawn down have been fewer. Practically speaking, there is little if any marsh land saturated with sea-water about Mystic pond.

Let us place side by side the analyses of the waters made at or near the time of their introduction for aqueduct use, with those of more recent date:

This exhibit is, at least, not prejudicial to the good repute of the Mystic water. It had, in 1860, of inorganic, 5.46; organic, 2.20; 1870, inorganic, 3.78; organic, 2.83.

What is the real significance of an accession of inorganic salts?

This topic has received a large amount of attention, in England, more especially. It is an interesting fact, the result of experience and observation, that the rates of mortality are not in the proportion of foreign inorganic matters present in town supplies of water, but in the ratio of their absence. That is, the nearer a water approaches absolute purity inside a certain normal limit, the less suited is it to meet the demands of the ordinary organism.

It used to be believed that a hard water that is, a water which, on account of its hardness, was less serviceable for laundry purposes was less healthful. was less healthful. But Dr. Letheby, of London, has made a collection of the death-rates of a large number of towns supplied by aqueducts, and placed these rates in a table side by side with the degrees of hardness of the water (the measures of salts of lime and magnesia) supplied to the several towns, and the result shows that the death rates rise with the increased purity of the water.

The degrees of hardness in the following table are relative, based on the curdling produced in the water by the addition of graduated solutions of soap in alcohol:

Table showing Hardness of the Water Supply and the Death-Rates.

Now, while it would doubtless be well to act with caution in applying the obvious deduction from this table, it may serve to relieve us of special solicitude in regard to moderate accessions of inorganic matter to the remarkably soft waters of our primitive district.

It may be remarked that the lime salts which make water hard serve in the formation of bones. Wheat, from which most of our bread is produced, contains an abundance of phosphate of potash, but rarely more than a trace of phosphate of lime. The juices of flesh contain large measures of phosphate of potash with relatively little of phosphate of lime. The deficiency in the food is made up in part by the lime derived from the drinking water.

It is obvious upon a glance at the foregoing that, so far as general natural agencies are concerned, the future of the upper Mystic pond water may be contemplated without solicitude. There is nothing in the way of organic or inorganic matter likely to be seriously increased from any natural condition of the basin.

There is, however, the second kind of consideration, which grows out of the presence on the tributaries to Mystic pond of numerous manufacturing establishments connected with the treatment of the hides of animals, in the washing, dressing and tanning of which large quantities of water are used, and then turned with more or less of care, or with no care, in regard to settling or purification, into the streams leading to the pond. Besides these there is an establishment for refining glue stock; and a glue factory hitherto in operation in one part of the basin is about to be removed to another. It is in view of these establishments, and the prospective domestic sewage of a growing population, that the future salubrity of the water is thought to be endangered.

The main channels through which the Mystic basin finds its outlet are Cummings' brook, Kendall's brook, Russell's brook, and the lesser tributaries to Horn pond and Wedge

pond on the west, and the Abajonna with its tributaries on the east.

It has been deemed desirable to ascertain what has been, and what is now, the effect of the more important factories upon the excellence of the water. The collections of water have been made at points immediately above and below these works, as well as at points nearer the sources of the trib u taries, and at various depths in the upper Mystic pond. Besides these, numerous deposits from the bottoms of the streams near factories, and at various distances from them, to determine the extent to which the deposits are carried, have been collected, and, with the waters, have been analyzed.

The analytical results are presented in the two following tables: