proceedings of the polytechnic association. 621 



Intensity of Solar Radiation. 



Father A. Secchi has communicated to the Comptes Bendus his observa- 

 tions on the intensity of solar radiation at difl'erent seasons, from which he 

 draws the following two conclusions: 1. That in the summer, the radiar 

 tion in the meridian is greatly enfeebled by aqueous vapor, so that with- 

 out it, we should have double the radiation. (It would be necessary to 

 verify this for high mountains, which would be well worth the trouble.) 

 2. That the absorbing force of vapor is very great, for we see that a 

 quantity of seven to eight millimeters, in excess, in the summer, produces 

 an absorption equal to that of the entire atmosphere of gas in the winter, 

 which would give for the vapor ninety-five times that of the air. But if 

 allowance is made for the greater elevation of the vaporous layer in the 

 summer, and for the phenomenon of thermochrose, which causes the first 

 layer to absorb more than the following, it must be admitted that Prof. 

 TyndalPs result, which makes it sixty times as much as air, is not far from 

 the truth. 



Bleaching Sponges. 



The process of Mous. Artus, is to first wash the sponges with a warm 

 and dilute solution of caustic soda; afterward with warm water. They 

 are then plunged into a bath consisting of a dilute solution of hvposul- 

 phite of soda, and some dilute hydrochloric acid. When suflBciently 

 bleached they are taken out, well washed and dried. 



The Chairman remarked that sponge is the skeleton of a zoophite. Its 

 chemical constituents are one atom of iodine, three of sulphux', five of 

 phosphorus, and twenty of fibroin. The latter substance is found in the 

 secretions of the silk-worm and spider, and consists of thirty-nine atoms 

 of carbon, thirty-one of hydrogen, six of nitrogen, and seventeen of oxy- 

 gen. No substance resembling fibi'oin has begn^found in the vegetable 

 kingdom, and for this reason the sponge is generally classed among ani- 

 mals by naturalists, although a few still regard it as a plant. 



Pearl Oysters. 



The three most important pearl fisheries are in the Persian Gulf, in the 

 channel between Ceylon and the main land, and the Tenevelly banks oppo- 

 site the Gulf of Manaar. The pearl fisheries have been known from time 

 immemorial. The London Intelleclual Observer, in an article on the last 

 named locality, says: " The pearl oyster is not, in reality, an oyster at all, 

 but is more allied to a mussel, having a byssus or cable by which it 

 secures itself to the rocks, one of the most important points in its organiz- 

 ation. The animal's foot is composed of a series of muscular films, and is 

 two and a half inches long when distended. On the lower side is an exact 

 mold for the formation of the byssus. When the animal desires to attach 

 itself to a rock, its foot is protruded, and after seeking a suitable spot, the 

 tip is still for some minutes, and then retracted into the shell. A strong 

 fibre in the form of the groove is left attached to the base of the foot at 

 jone end, and to the rock at the other. This prgcess is again and again 

 repeated, until a strong cable is formed. The animal can cast off this 

 cable, and reform one at pleasure, when in good health. Its food consists 



