270 



farmers' A^D mechanics' journal. 



Let C D, Fig. G2, represent a beam strained by a load at E, 

 and supported at the ends. All the parts above the middle of the 

 depth, b c, will be compressed, all below will be extended ; there- 

 fore, the square abutment a e is better for the upper side than any 

 complicated joint whatever; and it is evident, that all oblique 

 joints should be avoided on the compressed side. In this figuie 

 the whole of the strength of the lower side depends on the bolts 

 and strap. 



Fig. 62. 



The following figure shows another form, where the lower side 

 is indented so as not to depend wholly on the strap and bolts ; and 



Fig. 63. 



a key is introduced to tighten the scarf. It will readily appear, 

 th it had the joint been cut to the dotted line instead of the oblique 

 line, the strength would have been much impaired. 



The annexed figure represents an angular view of a scarf, where 

 it is jointed the contrary way. An iron plate at A B is supposed 



Fig. 64. 



to be removed, which shows the tongue at the end of the scarf. 

 This method appears to me to employ more of the strength of the 

 limber than any other, and is very well adapted for a tie-beam 

 where it is strained both across and in the direction of its length. 



In all these cases the depth of the indents, and the length of the 

 scarf, will be obtained by the same rules as for beams strained in 

 the direction of their length. 



In scarting beams to bear a cross strain, it would be a great ad- 

 vantage to apply hoops or straps instead of bolts, as the coach- 

 makers and ship-carpenters do. It would be easy to form the scarf 

 so that hoops might to be driven on perfectly tight. 



