44 ON THE LOSS OP HEAT 



same length, which in all other respects were similar. From 

 these experiments it will he seen, that the same length of pipe in 

 elbow joints is much more efficacious in imparting heat to the 

 room than straight pipe, and as the length of pipe producing 

 a descending current, was nearly equal in experiments No. 6 

 and No. 8, the great advantage which has been supposed to 

 be derived from the descending current, does not appear to 

 exist, although it is undoubtedly more efficacious than the same 

 length and position of pipe producing an ascending current, as 

 the velocity of the current in the former is diminished by the 

 increased resistance which must necessarily be overcome in its 

 descent, while the latter gives greater facility for the heated 

 air to escape than is given by any other position in which the 

 pipe can be placed. Experiment No. 7 shows that pipe placed 

 horizontally is more efficacious in imparting heat, than when 

 placed in a vertical position either for an ascending or descend- 

 ing current. 



The causes which operate to render the same length of 

 pipe in elbow joints more efficacious than any other con- 

 struction, may be satisfactorily explained. The shape of the 

 pipe forces the current of heated air to make abrupt turns, 

 in doing which it impinges against the elbows with sufficient 

 force to invert its internal arrangement, by which change from 

 its former relative situation with the sides of the pipe, a new 

 stratum of hot air from the interior of the current, is brought 

 more frequently in contact with the sides of the pipe, which 

 facilitates the process of imparting heat, particularly by being 

 brought in contact with the lower half of the horizontal part 

 of the pipe, which is necessarily the coldest from various causes, 

 and is of very little service in imparting heat to the room with- 

 out the aid of elbow joints. 



From experiment No. 8, an important inference may be 

 drawn ; that the advantage gained under ordinary circumstanes, 

 by increasing the length of the pipe, has a limit very far short 

 of that which is found to be necessary to impart all the heat 

 generated to the air of the room, as in this experiment, only 

 five parts of the heat were lost in using 13^ feet of pipe, con- 



