P OL YTECHXIC A SSOCIA TION Pr CEEDINGS. 739 



Ca^n or Portland stone. This solution l3y forming crystalized 

 diphosphate of lime, has the effect of hardening the surface of the 

 stone, and diminishing its capacity for absorbing water. 



TOPOGRAPHICAL INDICATOR. 



Mr. Bazal^ette described before the British Asssociation at 

 Dundee, his plan for supplying trustworthy topographical informa- 

 tion to all classes of tourists. On reaching summits in England, 

 commanding extensive views, there seems to be difficulty in obtain- 

 ing trustworthy local information regarding objects brought within 

 the field of the telescope. He proposed to supply such informa- 

 tion by means of a local indicator, consisting of a circular table of 

 stone or metal, engraved with radial lines pointing in the direction 

 of any object of interest. Upon the line would be engraved the 

 name of the object, its distance from the point of view, and, in 

 the case of mountains, their height above the sea. A table three 

 feet in diameter, would be sufficient to embrace a district of thirty 

 miles. To facilitate reference, concentric lines representing dis- 

 tances of five miles would be engraved; and beyond the outer 

 circle, might be placed maps of cities, cathedrals, &c., bej'oud the 

 distance of thirty miles. In the center of this table is to be placed 

 the telescope, and the whole is to be covered by a light ornamental 

 building so arranofed as not to obstruct the view. 



GIFFARD'S INJECTOR. 



Mr. J. K. Fisher illustrated upon the blackboard, his proposed 

 improvements on the apparatus for supplying a steam boiler with 

 water, by means of steam from the boiler itself. The steam current 

 carries particles of cold water with it, and being itself condensed, 

 its momentum is sufficient to carry the water into the boiler. 



Considerable discussion followed on the value of any injector 

 on Giffard's plan. The chairman said the injector was not in all 

 cases reliable, for the temperature of the water to be forced in, had 

 an important part to play in this mechanical paradox. The injector 

 is useful where water is to be forced into a boiler while the engine 

 attached to it is not in operation, and the pump which ordinarily 

 supplies the boiler is consequently motionless. 



THE BRIDGEPORT KNITTING MACHINE. 

 This machine, manufactured at Bridgeport, Conn., was exhibited 

 and operated before the meeting. 



The great advantage which the Bridgeport knitting machine has 



