422 



Mr. J. Morrow on an Instrument for 



an unusually large distance was allowed between the ends of 

 the specimen and the portion of it under observation. 



The instrument used was carefully measured under a read- 

 ing microscope and found to give a magnification of 4'10(). 

 The distance between the needle-points of the tilting mirror, 

 measured in the same way, was '2960 in. The normal distance 

 from the mirrors to the line through the scale parallel to the 

 tilting mirror was measured several times in diflPerent ways 

 and the mean value taken as correct. 



Under these circumstances the total magnificatipn obtained 

 was about 2800, but the exact value of course varied with 

 the position of the telescope and scale. 



Table II. contains the results of expeiiments on specimens 

 of various materials. 



The extensions and lateral contractions were measured 

 simultaneously, an extensometer having been specially 

 arranged so that both instruments could be attached to 

 the specimen at the same time and used throughout the 

 experiment. 



The calculated means of the observed tensile and lateral 

 strains for half -ton of load are given in the table, and the 

 values of the modulus of elasticity and Poisson's ratio are 

 obtained from these. The modulus is given in lbs. weight 

 per sq. inch. It can be expressed in grammes weight per 

 sq. cm. by multiplying the numbers in the table by 70*31. 



Table II. 



Material. 



Mild 

 Steel. 



Strains per § ton of Load. 



Young's 

 Modulus. 



Poisson's 

 Eatio. 



•276 

 •277 

 •273 







Tensile. 



•000,0464 

 •000,0469 

 •000,0465 



Lateral. 



•000,0128 

 •000,0130 

 •000,0127 



30^75 X lO'^ 



30-46 



30^70 



Sheffield 



Spindle 



Steel. 



•000,0488 

 •000,0505 

 •000,0488 



•000,0135 I 29-60 

 •000,0142 : 28-33 

 •000,0132 1 2923 



•277 

 •281 

 •271 





Wrought 

 ]ron. 



•000,0531 

 •000,0826 

 •000,0928 



•000,0144 

 •000,0239 

 •000,0251 



29-08 

 29-80 

 30^73 



•271 



•289 

 •270 



Dia. = -761 

 „ =-707 



Drawn Brass 



(Muntz Metal). 



•000,1047 

 •000,0978 

 •000,0960 



-000,0335 

 •000.0345 

 •000,0337 



13^26 

 14-23 

 13-61 



-320 

 •353 

 •351 





Drawn 

 Copper. 



•000,0770 

 •000,0726 

 •000,0822 



-000,0262 

 •000,0241 

 •000,0255 



17-61 



18^70 



16-88 



•340 

 •332 

 •310 





