(32) 



The accuracy of the manometer is about 2 %> which is quite suf- 

 ficient for our purpose. 



2. Direct measurement of the maximum strain T m by the deter- 

 mination of the breaking stress. 



In order to prevent as much as possible unequal strain during 

 the suspension we have used here glass threads of at the most 

 0.6 mm. thickness l ). 



In order to reduce the tensions to minimum the glassrod was 

 bent to a hook at either end. It was then suspended by the upper 

 hook and the rod was drawn out in the middle to a thread by 

 applying a certain force to the lower hook in about the same way 

 as in the actual experiment. The weight used was a beaker into 

 which water flowed. 



§ 3. Results. 



1. Determinations with cylindrical tubes and internal pressure. 



In order to facilitate a comparison with Galitzin's results we 



1 

 take the same value - for the coefficient of contraction. Let P m be 

 4 



the maximum internal pressure, 2R the external diameter, 2R' the 



r> 



inner diameter (this is further on expressed in mm), and letn= — , 



R 



then we can represent the maximum tension T m in the glass, (in 



this case that of the internal portions of the glass in a direction 



perpendicular to the axis of the cylinder) by : 



1 ( /p 1 



r m = -L 5P„, + 7 ( ±^i _ i 



4 ( V^n 2 — 1 



If, as is the case in the following tables, P m is expressed in 

 atmospheres, we find T m expressed in KG/mm* (as it is given in 

 the following tables) by multiplying the value found above by 0.01033. 



For the three series mentioned in § 2 sub a, b and c the results 

 have been combined in the table below. The meaning of the columns 

 will be clear after what has just been said. Where several results 

 are given under one number we have after the tube had partly 

 burst (for instance so that only the end had broken off, or the tube 

 had broken near the steel piece) used the same tube again for the 

 following experiment. 



The results for T m are lowest for series a and highest for series b. 

 In the last series this is especially the case for the tubes with a very 



l ) In the experiments of Winkelmann and Schott where thicker rods of 10 — 20 

 mM 2 . section were used this required great care. 



