2 
BULLETIN OF THE UNITED STATES FISH COMMISSION. 
JSTot assuming to be competent to affirm or deny Mr. Lloyd’s conclusions from liis 
standpoint or to form an opinion concerning attempts of this nature in European capi- 
tals, which were altogether different from the skeleton framework and light paper shell 
of the Central Station Aquarium, they having been built of stone and cement at great 
cost, I commend the idea as here employed on the score of economy, cleanliness, and gen- 
eral effectiveness. To have produced equally good results with wood or metal would 
have cost very much more. The advantages of such an arrangement are that, while 
the aquaria are afforded the light necessary for their success, it is cut off from the eye 
of the observer, except as it reaches it softened and diminished in passing through the 
water. A further advantage is that the attendants can carry on their work undis- 
turbed and without annoying or distracting the attention of the observer from the 
aquaria. It further prevents the introduction of food, or the interference of any kind, 
by visitors or those not properly authorized. 
Some unavoidable use of brass piping in the beginning demonstrated beyond any 
further need of experiment the necessity for the entire absence of metals from the 
tanks, reservoirs, and circulatory apparatus, and consequently the materials now used 
in their construction are glass, slate, hard and soft rubber, and wood, nothing being- 
used which is oxidizable or capable of exciting galvanic or chemical action. 
The use of an awning covering the entire structure affords the necessary protec- 
tion from excessive heat and sunlight in summer. 
A gas engine with hard-rubber pump supplies the means of elevating the water to 
a sufficient height to give the pressure necessary for effective aeration. 
The number of aquaria in the marine grotto is twenty-four, having an aggregate 
capacity of about 1,800 gallons of water. The elevated tank holds something over 400 
gallons. The reservoir, located in the yard of Central Station and inclosed with wood 
and glass, holds about 4,000 gallons of water, thus making a total of about 6,000 gallons 
in the circulation. The upper tank, being at an elevation of about 40 feet, gives a 
pressure of about 20 pounds to the water entering the aquaria. 
By passing the water through very small glass nozzles (one thirty-second to one- 
eighth inch orifice, as required) at this pressure a small amount of water suffices, as a 
very large amount of air is drawn in with it and dispersed throughout the entire body 
of water in an aquarium in minute bubbles, thus affording efficient aeration. 
In addition to this circulatory system, there is an auxiliary system of aeration, 
which is used in case of unavoidable suspension of the circulation, and is also valuable 
in special cases and in the aeration of water of other degrees of density than that in 
the main body of salt water. 
This system, devised by Hon. Marshall McDonald, is a modification of the various 
air-pumps in use, which are operated by a fall of water through tubes, and is so simple 
and efficient as to be of very great value, and within the reach of all, for the aeration of a 
single aquarium kept for amusement or for the greater needs of institutions of learn- 
ing. Artificial aeration, or change or circulation of water, is necessary where more 
than a certain proportion of aquatic animals are kept in a given amount of water. For 
the keeping of marine forms of life where the supply of salt water is necessarily limited 
and especially for the uses of biological laboratories, this device should prove of very 
great value. 
To establish such a pump there must be first a fall of water. As but a small 
amount is necessary for the operation of a single pump, it may be carried up from a 
