Prof. L. T. More on Eleetrostriction. 



11 



that is, one-fifth that of the present form. And this minimum 

 deflexion coukl be observed readily and measured accurately. 



When electrically charged the inner armature and the 

 tripod table were always grounded, and the outer one 

 charged by a powerful static generator, capable of giving 

 a spark eight inches long aiid 'of great volume. From one 

 to four large leyden-jars were placed in the circuit to pre- 

 vent irregularities in the charging.' The potential-differences 

 were measured by a spark-micrometer with balls two centi- 

 metres in diameter. With all the apparatus in the circuit 

 the highest potentials were reached in from ten to fifteen 

 seconds. To prevent any charge from reaching the tripod 

 table, it was inclosed in a cage of fine copper gauze wire, 

 which fitted over the top of the experimental tube and was 

 grounded. When the tube was disconnected from the circuit, 

 no disturbance reached the mirror, even though long sparks 

 passed across the terminals of the spark micrometer. 



The entire apparatus was fastened to heavy beams, bolted 

 to masonry piers in a basement room. No experiments were 

 made when the image showed any motion due to temperature 

 changes in the room during a period of time five or six times 

 that of charging. 



A convenient method of testing the apparatus is to make a 

 determination of the modulus of elasticity. The weights for 

 compressing the tubes were placed on a table with three legs 

 which rested on the glass tube only. Deflexions are expressed 

 in divisions of the micrometer. 



Table IV. — Modulus of Elasticity. 



Tube 3. 



- 

 Tube 4. 



Weight, 1000 gr 



60-5 div. 



61-0 



58-0 



56-0 



600 



59-0 



310 

 30-5 

 30-5 



30-7 



45-0 div. 



.550 



550 



51-7 



250 

 250 



250 



Weight, 500 gr 





