EIGHTH ANNUAL REPORT. 81 
the greatest value in nature study, in arousing the interest of the 
pupils, and are vastly more instructive than illustrations in the 
books. 
In response to numerous requests from biology teachers for as- 
sistance in establishing small study aquaria in the school-rooms, 
an expert from the Aquarium was detailed to visit all schools 
making application, and give the teachers practical instruction in 
maintaining these valuable aids to nature study. The coopera- 
tion of the Board of Education was secured; the Board agreeing 
to supply the teachers with aquarium jars and transport to the 
schools the necessary supply of sea-water. The collections for 
these aquaria are furnished free from the surplus stock at the 
New York Aquarium. About 100 small aquaria have already 
been placed in schools, both teachers and pupils taking great in- 
terest in them. The number is being steadily increased as teach- 
ers make application for them. This work is in the hands of Mr. 
L. B. Spencer, of the Aquarium. 
A small library of works on marine and aquatic life has been 
acquired for office purposes, and for the use of teachers and oth- 
ers studying the collections. 
DENSITY OBSERVATIONS AT THE AQUARIUM. 
The remarkable conditions under which sea fishes have always 
been kept at the Aquarium rendered it desirable that regular ob- 
servations be made on the density of the water. Ocean salinome- 
ters were secured and the results of a year’s observations show 
some very interesting conditions, especially with respect to fishes 
from the Bermuda Islands, where ocean densities are probably 
at their highest. While it is a fact that some of these fishes live 
in the Aquarium for months, and even for years, the majority of 
the species in each collection brought from that region do not 
survive many weeks. 
Injured fishes, that have been bruised at the time of captivity 
and during transportation, frequently heal in a short time if the 
density of the water happens to be at its highest when they arrive 
at the Aquarium. Should the density be low, they are apt to die 
much sooner, as their injuries do not heal under such conditions. 
Should the Hudson River be high when new fishes, either tropical 
or local, are received, the mortality is apt to be greater than when 
the river is low. The highest death-rate among the sea fishes 
that the Aquarium has had for some time followed the heavy 
floods of the past summer. During the winter and spring the 
densities are much lower than in summer. 
Sea fishes living in water of low density are affected in other 
