REVERSED AND NON-REVERSED SPECTRA. 



91 



ture convex upward; in the sixth series the tube was additionally supported 

 in the middle on a large pendulum-like wire or hanger. 



TABLE 20. 



The individual results are shown in figures 59 and 60. It will be noticed 

 that an error was introduced when pressures passed from the increasing to 

 the decreasing phase at the highest pressure, and this was particularly the 

 case when a slight leak developed. If the highest pressure is omitted, io 6 AL 

 = 14.7, both for increasing and decreasing pressures in the case of the sus- 

 pended tube. Hence k = i.25oX io 6 , not differing essentially from the above. 

 The unsupported tube is highly subject to viscosity. 



500 8 dim. 



The large effect resulting from viscosity is also shown in the initial and 

 final readings (100 atmospheres) in figures 59 and 60. It is in both cases 

 again an apparent contraction and is present even in the supported tube. 

 The viscous effect in the lapse of time is directly given in the following inde- 

 pendent measurements of apparent contraction. The tube was kept charged 

 with an internal pressure of 100 atmospheres. 



Time 9 h 3o m io h 5 m i2 h i2 ro 



Length, L 0.0173 0.0183 0.0206 cm. 



It is difficult to understand, however, how anything of the nature of vis- 

 cous longitudinal contraction can occur under internal pressure. One might 



