PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 469 



is put in the string- at every revolution around the card; but if the card is 

 shifted to the right hand and the winding continued with the left, the 

 twists arc taken out, or the thread is twisted in the opposite direction. 

 The same action takes place in ordinary sewing by hand, a twist being 

 put into the thread or taken out at every stitch. It is for this reason that 

 girls are taught to work button holes always in the same direction, going 

 from left to right along the lower edge, and from right to left above when 

 "twist" is used. The twisting is avoided in winding thread by adopting 

 the method usually practiced by boys in winding their kite strings. To 

 avoid kinking or spoiling the thread from the twisting in sewing, thread is 

 cabled, as it is called; that is, it is first spun into thread, and then these 

 are twisted together. In sewing on sewing machines, no twisting of the 

 thread takes place, it is therefore not necessary to cable the cotton for this 

 use. 



The Chairman pi'esentcd the following interesting compendium of late 

 scientific investigations: 



Action of Ozone on Silver Haloids. 



Statements in foreign journals that ozone generated by electricity is 

 capable of giving sensitiveness to insensitive iodide of silver, led Mr. Carey 

 Lee, of Philadelphia, to make experiments in this direction with ozone 

 generated by chemical means, by phosphorus, and by the action of sul- 

 phuric acid on the cameleon mineral. The result of a great variety of ex- 

 periments described in the January number of the Americun Journal of 

 Science and Art appears to show pretty clearly that ozone has no power of 

 giving sensibility to insensitive iodide or bromide of silver, formed in the 

 presence of excess of alkaline iodide, when such excess is removed, or when 

 the excess be left present, as was the case with the alkaline bromide. 



On the Separation of Metals. 



Dr. Wolcott Gibbs, Rumford professor in Harvard University, has con- 

 tributed to the January number of Silliman's Journal very valuable pro- 

 cesses: First, for the separation of chromium from metals belonging- to the 

 group analogous to iron. Second, for the separation of aluminum and iron 

 from other bases by means of acetate of sodium. Tiiird, for the separation 

 of manganese from cobalt, nickel and zinc. Fourth, for separating cobalt 

 from nickel. Fifth, for separating uranium from zinc, cobalt, and nickel. 

 Sixth, on analysing copper and nickel by means of their electrolytic precip- 

 itation. 



Petroleum Wells, 



The borings for oil in Western Pennsylvania are made through three 

 strata of sandstone. The oil found immediately below the first stratum is 

 thick and heavy; that just below the second stratum is lighter, and that 

 from the greatest depth, forming the flowing wells, is clear, limpid, and 

 lightest. Such is the testimony of Mr. Ira Sayles, in Silliman's Journal. 



Prizes for Meteorological Observations. 



The Frencli association for the advancement of meteorology, now under 

 the presidency of Le Verricr, offer a prize of 4,000 francs for an extended 



