218 PROCEEDINGS OF THE ACADEMY OF 



December 1. 

 The President, Dr. Ruschenberger, in the chair. 

 Thirty-three metabers present. 



0^? Specific Gramty. Prof, Letdy remarked, that, in taking the 

 specific gravity of minerals by means of the scales in weighing the 

 substance in water, the usual plan was to suspend it from one side 

 of the instrument by a delicate thread or hair. The attachment 



of the specimen was tedious 

 and often difficult, especially 

 in the case of small crj'stals 

 and polished gems, from 

 which the hair would slip, 

 and could only be made to 

 retain its position by caus- 

 ing it to stick with some ad- 

 hesive matter. He dispensed 

 with the thread or hair, and 

 substituted on one side of 

 the balance a double dish, 

 as represented in the figure. 

 The lower dish is perforated, and is kept suspended in a glass of 

 water. After weighing the specimen in air in the upper dish, it 

 is simi)ly necessarj^ to change its place to the lower dish to weigh 

 it in water. 



Coloring of Autumn Leaves. Mr. Thomas Meehan presented 

 some leaves sent to the Academj'- from the West, illustrating the 

 influence of light in coloring autumn leaves. They were of the 

 red or swamp maple, Acer rub7-um,, and had been fastened in pairs 

 by a spider's web. The uppermost leaf, obstructing the sun's 

 action on a portion of the lower, had prevented any change of 

 color in the unexposed part of the lower leaf, and thus the exact 

 form of the upper was photographed or outlined on the lower one. 

 Mr. Meehan said there was nothing new to science in this observa- 

 tion, as orchardists were well aware that the coloring of apples 

 and pears was deepest on the sunny side ; and that when entirely 

 shaded from the sun, by over-hanging leaves or branches, they 

 were almost colorless. 



This fact was often taken advantage of to photograph names 

 liy stencilled paper on fruits. At the Great Sanitary Fair held 

 during the war, fruit with names of Grant and Lincoln thus " sun 

 burnt" on them, brought good prices. 



Still it was well to remember that the sun could not be the sole 

 cause of color. Apples exposed to the same sunlight would be 



