34 



SMITHSONIAN CONTBIBUTIONS TO KNOWLEDGE 



VOL. 



These cylinders were sel in a light frame at an angle of 25 with each 

 other, or 12.5 with the median line of the aerodrome, and drove the long pro- 

 peller shafts as shown in Plate 10, No. 0. At the extreme forward end of the 

 crank-shafts there was a pair of intermeshing bevel years which served to main- 

 tain the rate of revolution of the two propellers the same. 



The boiler built for this work was a beehive-shaped arrangement of coils 

 of pipe. It consisted at first, as shown in Fig. 3, of three double coils of |-inch 

 copper pipe coiled up in the shape of a truncated cone, carrying in the central 

 portion a pear-shaped receiver into the upper portion of which the water cir- 



ri.;. ::. Boilers in use in 1891-1892. 



culating through the coils discharged. Each of these receivers was connected 

 at the top with the bottom of a Long cylindrical drum, with hemispherical ends, 

 which formed a steam space from which the supply for the engines was drawn. 

 The lower ends of the coils were connected with an injection pipe supplying the 

 water. Each " beehive " had 23 turns of tubing, and had a base of 7.5 inches 

 and a top diameter of 6 inches, the steam drum being 2.5 inches in diameter. I 

 may here say that in the selection of the general type of boiler for the work to 

 be done, there was never any hesitation regarding the use of the water-tube 

 variety. Their superiority for the quick generation of large volumes of steam 

 had been so pronounced that nothing else seemed capable of competing with 



