262 U. S. BUEEAU OF FISHERIES 



moving the glass, a troublesome procedure that would necessitate the 

 temporary emptying of numerous well-stocked tanks. With a total 

 of 455 linear feet of plate glass, mostly in this condition, the outlook 

 is not reassuring. Visitors should not be permitted to tap the glass 

 with canes or umbrellas, as when under water pressure cracfe are 

 started easily, 



LIGHTING THE TANKS 



No artificial lighting of aquarium tanks can take the place of the 

 light of day. In the construction of the aquarium building it is im- 

 perative that skylights be made large enough to admit diffused day- 

 light in abundance. As aquarium tanks nearly always are located 

 on the ground floor, usually many feet below the roof, the light should 

 be strong enought to show what the tanks contain and to reveal the 

 natural colors of the occupants. Natural colors are obscured and 

 their values more or less altered by artificial light. 



The principal defects in the temporary aquariums operated by the 

 United States Fish Commission at industrial expositions held in 

 American cities were essentially those connected with the lighting 

 of the tanks. While the architects insisted that the skylights as 

 planned would furnish sufficient natural light, it became necessary, 

 upon installation of the exhibits, to add artificial light, Avhich re- 

 sulted in decided impairment of effect as well as greater cost of main- 

 tenance. Objects under water can not be seen clearly with diffused 

 daylight that would be sufficient for ordinary museum purposes, 

 while the illumination of water by artificial means is correspondingly 

 more difficult. Skylights located at a considerable height above the 

 tanks should be decidedly larger than when placed lower down. 

 When light is stronger than necessary it can be reduced easily by 

 shading. Direct sunlight on the water is undesirable. 



ROCKWORK 



At most public aquariums it is customary to line some of the tanks 

 with rockwork, with the view of avoiding monotony and providing 

 something like natural backgrounds. When this is well done the 

 attractiveness of the exhibits is enhanced greatly. The material used 

 is cemented to the walls of the tanks. It is possible, by such means, to 

 produce the effect of reefs and grottoes, but the success of under- 

 water pictures created in this way is dependent upon good taste and 

 a knowledge of what is appropriate in each case. It is not the kind 

 of Avork that can be left to the contractor. In some cases artificial 

 submarine views are not very convincing. 



Coral rock from Florida or Bermuda reefs is good material to 

 work with. A fair substitute is the calcareous tufa used about green- 

 houses and by gardeners in the construction of rude fountains. 

 Masses of hard, cavernated bowlder clay rock of a dark sliade, ob- 

 tained along the coast at low tide, have been found suitable for pro- 

 ducing the effect of sea-worn rocks. Conglomerate rock is permissible 

 for both fresh and salt-water tanks. It is easier to find the materials 

 than the genius to combine them so as to produce natural effects. In 

 the lining of fresh -water tanks attempts have been made to reproduce 

 the rocky banks of streams and lakes. A ledge of columnar basalt 



