ivhen driven into different species of Timber. 41 



oak, and equally seasoned locust. Thus the weight which in those 

 three cases drew the square spike from chestnut, was 1995 ; and 

 that which extracted the broad flat one 2394 ; and that which 

 drew the narrow flat one from the same timber was 2223. The 

 sum of these is 6612. The sum of the three numbers for the same 

 three spikes used with oak, w'as by experiments 5, 6, and 7, 13110; 

 and the sum of the three in locust, by experiments 13, 14, and 15, 

 is 18280 ; these three numbers have to each other the relation of 

 1, 2, and 2| ; from which we infer that oak is almost precisely twice, 

 and locust 2f times as retentive as unseasoned chestnut. By com- 

 paring together the results of experiments 1 and 2, it will be seen 

 that the weights required for extracting the two spikes respectively, 

 are more nearly proportional to the breadth than to either the thick- 

 nesses, or the weights of the spikes. For the spike with a breadth 

 of .405 inch and a thickness of .402, required 1995 lbs. for its 

 removal, while that which had a breadth of .375 inch took 1873 

 lbs. Now .373 : 405:: 1073 : 2033 for the calculated retentive- 

 ness, instead of 1995, as given by experiments ; — a difference of 

 only +38 lbs. between the observed and calculated results. Cal- 

 culating the retention by the iveights of the respective spikes, we 

 should have 866 ; 942: : 1873 : 2987, or a difference of 42 lbs. 

 while using the thickness alone, we obtain .384 : 402:: 1873 : 1960, 

 a difference of an opposite kind of 35 lbs. from the observed result, 

 the greater thickness yielding the less retentive power. This cor- 

 respondence between the breadths and the extracting weights be- 

 comes still more apparent when we compare the third, and especially 

 the fourth with the second experiment. Thus for the broad flat 

 spike, (3d Ex.) — compared with experiment 2, we obtain 

 By breadths, .373 : 539 : : 1873 : 2701, instead of 2394, diff. -f 307 

 " weights, .866: 898:: 1873: 19-12, ''■ " " - 452 



" thicknesses, .384: 288:: 1873: 1379, " " " -1015 



and for the thinner and lighter spike, (Ex. 4th.) — compared with 

 the same. 



By breadths, .373 : 390 : : 1873 : 1958, instead of 2223, observed diff. - 265 

 " weights, .866: 566:: 1873: 1224, " " " " -999 



" thicknesses, .384: 253:: 1873: 1234, " " " " -989 



Nearly the same conclusions would result from a comparison of 

 those trials, which were made on seasoned white oak and locust. 

 Indeed, it appears that with a given breadth on the face of the spike, 

 a diminution of thickness is sometimes a positive advantage to the 

 retentiveness of the timber ; for in white oak, the spike which had 



Vol. XXXIL— No. 1. 6 



