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Page:Popular Science Monthly Volume 89.djvu/379

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Popular Science Moiillili/

��36.5

���As the Water Passes Down from the Top of the Ladder It Flows Through the Notches in the Bottoms of the Cross-Pieces into the Next Lower Sec- tions, Thus Making Miniature Waterfalls

��water between an\- cross-pieces finds a

��Iwo consecutnc horizontal levc determined by the depth of the notch in the lower of the two pieces. As the water passes down from the top of I he- ladder it flows through the notches in the bottoms of the cross-pieces and also tlrops o\er the top notches in the cross- pieces into the next lower sections like small waterfalls.

The water in the ladder is continualK' flowing down and out at the bottom, forming a running stream up which the fish may swim with a choice of passing from the first pool to the next and so on up by swimming through the bottom notches or jumping through the top notches from one pool to the next higher one. The jump in the latter case is not more than eight inches and can be done easily by almost any kind of fish.

It is noted in the plan view of the ladder shown in the accompanying drawings that the notches in the bottom of the cross partitions are placeil at the lower end of the partitions to permit any sediment to be washed out by the llow of water. In the large drawing it is also to be noted that the ladder is not placed in close proximity to the spillway. The reason for this is that fish in trying to ascend a dam seek to pass up the largest stream of running water. Due to the fact that the \'olumeof running water issuing from the ladder is usually less than that

��dropping over the spillway, the fish would not find the ladder readily if it were close to the spillway but would try to swim up the spillway and would probably dash themsehes to death against the concrete buttresses.

��Borrowing the Night Lamps of the Fireflies

Just what the secret of the firefly's light is the scientists have not as yet discovered. Three necessary factors have been found — water, oxygen and a photogenic orlight-producing substance; but a fourth is probably involved which has thus far defied all research. The children say it is the fairy lamplighter whose wand lights the little lamps that add so much to the beauty of a sum- mer's night. However, a method has been evohed of extracting and drying the light-producing organs of the fireth' without impairing the power of the substance to phosphoresce.

The dried material may be extracted with water-free solvents. It is ground up into a powder, and water containing oxygen is atlded ; which gives the golden glow without the assistance of either the firefly's will or the fairy's wand.

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