Peoceedixgs of the Polytechnic Association. 979 



tliG power of sunlig-lit is vcr}- varialtle, for cletcnniiiing liuw long 

 exposure will be required to produce a ])hotograph. 



HoT-AiR BY Wholesale. 

 A geutleinen who has l)ceii for mnny years engaged at the United 

 States Arniorj, Springfield Mass., is now making experiments to 

 ascertain whether it is feasible to supply an entire city with heated 

 air. lie proposes to heat the air by means of iron and fireclay pipes 

 to about 600 degrees Fahrenheit, and to force it through tubes, 

 covered with a non-conducting substance, to the place wdiere it is 

 to be used. The first trial will be made with a pump of eight-inch 

 diameter, which is to force the heated air through a series of clay 

 tubes of four-inch 1)ore for a distance of 300- feet. We infer that the 

 projector of this plan supposes tliat, l)y heating the air to a very 

 high temperature, he will be able to diminish greatly the quantity of 

 air to be moved, but a little -calculatii^n wdll prove that even this 

 arrangement will not enable him to supply a city with warm air, 

 even from a dozen different sources. It is, however, possible to heat a 

 connected square of buildings, abounded by four streets, by means of 

 steam-pipes, with less expense, less danger from fire, and far less 

 danger to health than by the transmission of hot air. 



Proposed Ship Canal. 

 A ship canal through the narrow^ neck of land separating Buzzard's 

 bay, fronj Cape Cod bay, Mass., is about to be commenced. The 

 canal will be five or six miles long, 300 feet wide, and twenty-four 

 feet deep at low water. This improvement will shorten the passage 

 of vessels between 'New York and Boston several hours, and enable 

 their navigators to avoid the open and often stormy sea encountered 

 in the voyage aronnd (Jape Cod. 



Navigable Passage Through PekpetJial Ice. 

 The Russian papers announce an important discovery b}' Cartson, 

 a learned Norwegian, which will give a great impetus to Siberian 

 trade. He had cruised, for scientific purpose?, in an ex])edition 

 nndertaken last summer in the Karian sea, Avhich washes the 

 southern part of the isle of Xova Zcmbla, and tlie government of 

 Tobolsk, and is covered witli eternal ice. In tliis ice a passage was 

 discovered which, for several months in the year, offers a convenient 

 path for traffic between Siberia and the Norwegian harbor of Iromsoe. 



