326 MEMORIAL OF JOSEPH HENRY. 



Experiments mi Building-Stone. — In 185 I. a scries of experiments 

 on the strength of differenl kinds of building-stone, was undertaken 

 liv Henry as one of a commission appointed by the President, 

 having reference to the marbles offered for the extension of the 

 I T 1 1 i i c 1 1 States < !apitol. Specimens of the different samples — accu- 

 rately fin to cubical blocks one inch and a half in height, were first 

 tried by interposing a thin sheet of lead above and below, between 

 the block and thesteel plates of the crushing dynamometer. "This 

 was in accordance with a plan adopted by Rennie, and that which 

 appears to have been used by most if not all of the subsequent 

 experimenters in researches of this kind. Some doubt however 

 was expressed as to the action of interposed lead, which induced a 

 series of experiments to settle this question; when the remarkable 

 fact was discovered that the yielding and approximately equable 

 pressure of the lead caused the stone to give way at about half the 

 pressure if would sustain without such an interposition. For 

 example, one of the cubes precisely similar to another which with- 

 al 1 a pressure of upwards of 60,000 pounds when placed in 



immediate contact with the steel plates, gave way at about 30,000 

 pounds with lead interposed. This interesting tact was verified in 

 a -erics of experiments embracing samples of nearly all the mar- 

 bles under trial, and in no case did a single exception occur to vary 

 the result. 



"The explanation of this striking phenomenon (now that the 

 fact is known) is not difficult. The -tone tends to give way by 

 bulging out in the centre of each of its four perpendicular Inc. -. 

 and to form two pyramidal figures with their apices opposed to 

 each other at the centre of the cube, and their bases against the 

 steel [dates. In the ease where rigid equable pressure is employed, 



as in that of the thick steel plate, all parts must give way together. 



Bui in that of a yielding equable pressure as in the case of inter- 



# 



ilcn Inpmcnt, and . volution, so generally confounded by the superficial. What may 

 i H . called the radical difference between these two views o! organic extension, is 

 that the former assumes an inherent mysterious tendency to progression, whose 

 motto i- ever "excelsior;" while the latter assumes a general tendenej to vari- 

 i within moderate limits in indefinite directions; so that elevation is no 

 more normal than degradation, and indeed may be regarded as rarer and more 

 exceptional, since at every upward stage attained by the few, there are probably 

 inure further digressions downward than upward, the motto being ever "aptior." 



