NINTH ANNUAL REPORT. 99 
An increasing number of teachers from the public schools and 
other educational institutions have visited the Aquarium with 
their classes. They have had the freedom of the large labora- 
tory on the second floor, where living corals, marine worms, 
and other delicate organisms afford opportunity for elementary 
instruction in natural history. 
DENSITY OBSERVATIONS AT THE AQUARIUM. 
Daily observations respecting the fluctuating density of the 
salt water used at the Aquarium were continued during the year. 
Reference has been made in previous reports to the fact that 
the sea fishes at the Aquarium have always been kept in brack- 
ish water. The accompanying table of monthly mean densities 
for the year, shows that the so-called salt-water averaged about 
half fresh from month to month. The daily records, however, 
show that during many weeks, from March to June, the water 
was fully three-quarters fresh. In fact, the daily observations 
of 1903 contain many consecutive records of density as low 
as 1.006: 
MONTHLY MEAN TEMPERATURES AND SPECIFIC GRAVITIES AT THE 
NEW YORK AQUARIUM DURING THE YEAR I90O4. 
(From the daily observations made by Mr. W. I. DeNyse.)* 
Temperature 
Months. of water. Specific gravity. 
AATIM ANY: ice cla eee: 34 1.014 
MED GUA one net 33 1.014 
ULE Nigel cP eee eas Hae near 36 1.013 
fe glee aac tee ak at eer 40 1.009 
INN Abe ties eer nie anes eae 52 1.010 
"fae aere ete atin a eee 61 1.010 
Ufialiyere teeth isis efor 70 1.013 
PNUIS USO ley Wat ceaieays.s 25: Fal 1.014 
Sepremivete sence oe 68 1.014 
Octobereeas en shc0is. 59 1.013 
IN@VEMDED 2 bd encase 51 1.013 
December (for 26 days) 39 T.015 
Most sea fishes cannot live long in water so nearly fresh as 
the above record shows it to be. If it were not for the fact 
* Density observations were made with samples of water brought to a tem- 
perature of 60° Fahr. 
