TIMBER FOR AEROPLANE AND PIT-PROP PURPOSES. 



93 



Others were received with the bark removed and were of course 

 tested in that condition ; it must be borne in mind that in the 

 case of the unbarked props the figure given in the tables for the 

 diameter at the centre of the prop is not the diameter over the 

 bark but the actual diameter of the wood at the centre of the 

 prop, as calculated from the mean cross-sectional area deduced 

 from rubbings of the top and bottom faces of the prop taken 

 before the test (see Transactio?is vol. xxxvi. p. 6i). 



The tables printed on pages loo-iio give the more important 

 results obtained in the 1920 and 1921 series of tests, classified 

 under the different woods, and for purposes of comparison with 

 the results of the 1918 tests the following table has been 

 prepared : — 



Summary of Compression Tests of Pit-Prop Timber. 



