NINTH ANNUAL REPORT. 99 



An increasing- number of teachers from the pubHc 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 historv. 



DENSITY OBSERVATIONS AT THE AQUARIUM. 



Daily observations respecting the fluctuating density of the 

 salt water used at the Aquarium w-ere 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 ]\Iarch to June, the water 

 w^as 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 I904. 



(From the daily observations made by 'Sir. W. I. DeNyse.)* 



Temperature 



^lonths. of water. Specific gravity. 



January 34 1.014 



February 33 1.014 



March 36 1013 



April 40 1.009 



May S^ I 010 



June 61 1. 010 



July 70 1.013 



August 71 1.014 



September 68 1.014 



October 59 1.013 



November 51 1013 



December (for 26 days) 39 1.015 



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 brouglu to a tem- 

 perature of 60° Fahr. 



