PnOCBEDIXGS OF TUE POLYTECHNIC ASSOCIATION. 999 



the one to coinmaiul sup^^ly, and the other to make the heavy traffic 

 disappear from the surface, which, he says, can best be done by 

 liavinrrbeneatli the markets underground railway branches connected 

 with all the main lines, bo that the products from agreat distance can 

 be brought to the stalls without transhipment, and in the same man- 

 ner articles purchased at the market could be forwarded directly 

 therefrom to any part of the kingdom by rail. It seems a plain pro- 

 position that there cannot be too many approaches to a great public 

 market ; and there are many other imprcjvenients of a scientific and 

 sanitary character yet to be made in all structures of this class. 



Pai'uyoxyle, 

 This compound, used as a substitute for pyroxyline in photograghy, 

 is perfectly soluble in a mixture of alcohol and ether. The absolute 

 absence of structure produced by a complete solution is said to 

 increase tlie sensibility of the iilm. Dr. Liesegang publishes in a 

 foreign journal liis process for making papyroxyle. . He plunges line 

 tissue paper into a cold mixture of equal volumes of sulphuric acid 

 of the usual strength and nitric acid of 1.40 degrees. The paper 

 remains in the mixture until a portion of it can be completely dis- 

 solved in a mixture of equal parts of alcohol and ether. Diiferent 

 varieties of paper require slightly different proportions of acid to 

 form the mixture. The paper on being withdrawn from the mixture 

 is hung over strings, and may be completely dried in half an hour. 



The Bahamas Hurricane. 

 Mr. John H. Eedfield of Pliiladelphia, son of the late "William C. 

 Redfield of ISTew York, author of the theory of cyclones, has made 

 a diagram of the directions of the wind at thirty-four different points 

 at noon on the first day of October, 1866, from observations col- 

 lected by Governor Rawson, W. Rawson, C. B. and Captain W. H. 

 Stuart, Bahamas. From the letter of Mr. Iledfield, accompanjang- 

 the diagram, we learn that at the time mentioned the center of. the 

 hurricane was but a few miles southeastward from Shroud Cay, the 

 wind at that Cay being from the northeast .tiutil one p. m., when there 

 was a lull of an hour, followed by a gale .from the southwest. The 

 line of progress of the axis of this storm,.after leaving Turk's Island, 

 seems to have been almost identical with »that of the Antigua hurri- 

 cane of August 22d, 181S, which also passed over the Bahamas, 

 beginning its easterly recurvature also about latitude twenty-eight 



