390 REPORT OF NATIONAL MUSEUM, 1903. 



DISTANT HEATING. 



The distances which in Dresden are taken into consideration in the 

 establishment of the distant-heating- phmt for the museums, etc., hold 

 a middle place between American district-heating systems and distant- 

 heating estal)lishments, but incline more toward the former. 



The New York Steam Company has established a great district 

 steam heating system with several boiler houses in the lower part of 

 the city almost from the Battery to the other side of the city hall, 

 1,500 yards up Broadway, extending about half that distance east and 

 west in the side streets; altogether about 8 miles of pipe. Among 

 other great buildings included in this system are the post-office. Mills 

 Building with ten stories, and Manhattan Life Building with its 350- 

 foot tower. The amount of steam furnished (including power) is said 

 to be satisfactory, but the returns are not considerable. Such district 

 heating establishments are to be found iii Lockport, Detroit, Phila- 

 delphia, Washington, Hartford, etc., but all except one are out of 

 use, as they did not prov^e a success. On the other hand, district 

 heating S3'stems have lately been combined with electric plants by 

 utilizing the exhaust steam, as in Springtield, Illinois, and in other 

 cities. For the financial success close proximity of the heated district 



ife prisms of the frozen windows by glass prisms and to give the glass prisms a regular 

 arrangement in place of the irregularity of the ice crystals. Another part of the 

 problem to solve was to regulate the direction of the rays falling in at random. 

 Everything was already fully accomplished by the Fresnel lenses in the light-houses. 

 It was therefore only necessary to remodel this costly contrivance so as to adapt it to 

 other uses and to cheapen it enough to bring it within reach of the general public. 

 This the Luxfer Prism Company succeeded in doing. It manufactures out of plain, 

 colorless, hard-glass mold small, strong window panes, with one surface plain, but the 

 other fluted with deep parallel grooves. By means of these furrows they obtain 

 strong strips of glass, to which are given the form of distinct-angled, three-sided 

 prisms. The jirisms have a common basal surface, parallel to the plane surface of 

 the plane, and their corresponding surfaces are likewise parallel. (See fig. 28.) 



If rays of light fall upon the plane, they are not conveyed on in the same direc- 

 tion, as in the case of ordinary window glass, but are refracted to an angle bearing a 

 definite relation to the angle of the prisms. (Fig. .31.) 



If we take a window consisting of nothing but prism panes, all of whose prisms 

 lie parallel, all rays of liglit will strike into the room in a parallel direction. It is 

 easy to understand that by a different arrangement of the prism panes or certain 

 portions of them, rays can be conducted into any desired parts of the room. 



But all poorly lighted rooms do not have such spacious windows as supposed in 

 the above description. A very large number of rooms lie below the level of the 

 street. Their small windows and the poor light of the generally large rooms limit 

 their use to a great extent. These windows, whicli are placed in a narrow shaft and 

 often scarcely rise above the level of the street, ex(;ludes the use of those prism panes 

 becaust- the amount of lighi (-oming in trom the sky is entirely too narrow. This 

 difficulty has been ol)viated by the construction of a i)articular kind of prism. 



The mass of light would become greater if the liglit shaft could be made larger, 

 l)ut traffic on the street forbids that. 



It therefore became necessary to find some contrivance which would make it 

 possible to enlarge the light shaft without interfering with the street traffic. The 

 light shaft is covered Ity a i)late consiHting of i)risms. This plate is composed of very 



