OP ARTS AND SCIENCES. 69 



in the Academy's set of their publications, moved, and it was 

 voted, — 



" That the special thanks of the Academy be presented to 

 these institutions for their marked interest and courtesy in 

 this behalf, and for their very valuable gifts." 



Mr. Thurber of New York, by permission of the Academy, 

 exhibited an ingenious adaptation of the pantograph, by which 

 partially paralytic persons, unable to write in the ordinary 

 way, may write with great facility. 



Four hundred and eiglity-seventli meeting. 



October 9, 1860. — Monthly Meeting. 



The President in the chair. 



Dr. Hayes, in presenting a " Eeport on supplying the City 

 of Charlestown with pure Water, made by Order of Hon. James 

 Dana, Mayor, by Messrs. George R. Baldwin and Charles L. 

 Stevenson, Civil Engineers," remarked, that 



Chemical analysis presents points of interest relating to the com- 

 position of the water of Mystic Pond. The results obtained on care- 

 fully selected samples of this water, recorded in the Report, show 

 a great variation existing at different parts of the mass of water. 

 The weights of solid matter found in a standard gallon, are 4.08 gr., 

 4.64 gr., 15.52 gr., 16.88 gr., and 58.64 gr. Below a certain depth, 

 the nearly pure water of this pond reposes on a heavier saline 

 water. Further observations have shown that this saline water, closely 

 resembling sea-water, maintains a nearly constant level in relation to 

 the purer water reposing on it, and that the saline diffusion is appar- 

 ■ ently veiy slight in amount, or very slow in point of time. Change 

 of temperature does not cause an intermixture of the two kinds of 

 water ; as the lower stratum has a density superior to that of the 

 pond-water at its greatest density, and, physically, the conditions of 

 repose are nearly the same, so far as penetration is concerned, as if a 

 saline sand-bottom held the place occupied by the heavier water. 



This pond, containing two kinds of water, can support the plants and 

 animal oraranisms of fresh water and of ocean water at the same time. 



