98 NATURE AND THE CAMERA 



taken were my ideas on the subject. Absolute clear- 

 ness of water is highly desirable, but almost impos- 

 sible to obtain. After straining the water so that it 

 is clear enough for ordinary work in a good light, 

 take an apparently clean stone, not a smooth marble 

 of course, but an ordinary, moderately rough stone, 

 drop it into the aquarium, and watch the result. 

 The water will be seen to be filled with a muddy 

 substance, and instead of crystal-like clearness we 

 have a murky-looking water that is most undesirable. 

 But your troubles have only just commenced. Add 

 some fresh green aquatic plants, and you will notice 

 that they too give off scum and muddy material, 

 even though they may have been placed in the water 

 with the greatest of care. Now when the fish runs 

 amuck through these beautiful plants, and really. dis- 

 turbs the mud and scum, the water has lost all its 

 clearness, so that it is absolutely impossible to photo- 

 graph a fish through it. With tropical aquatic vege- 

 tation the difficulty is even greater than with our 

 more simple northern plants. 



The beautiful ''sea-feathers'' that one sees waving 

 about with every movement of the water in the 

 tropical seas appear to be a clear, clean yellow or 

 purple ; but on putting them into the aquarium they 

 will be found to discolour the water immediately. 

 "Sea-caps" are even worse, and sponges cause so 

 much trouble that after a few discouraging attempts 



