570 wick. 



sure upon at least three specimens of the glass produces an effect 

 which is similar to that produced by lowering of temperature. 

 Gibbs, 17 in his work upon colored glass at high temperatures, found 

 that the effect of heating is, in most cases, to increase absorption and 

 to shift the absorption bands toward the longer wave-lengths. Gib- 

 son, 18 in a study of colored glass at low temperatures, found that the 

 transmission becomes greater at low temperatures and that absorp- 

 tion bands are generally shifted toward the violet. A specimen of 

 orange glass was found by him to become more yellow at —180° and 

 a brilliant red at 430°. A similar increase of transmission and shift 

 of absorption bands toward the red with increase of pressure has been 

 described in the case of glasses of red and orange color, G 20, G 34, 

 and G 36. 



Synthetic Ruby. 



A synthetic ruby 2.8 mm. thick kindly furnished by E. L. Nichols, 

 showed a small change in absorption at pressures up to 1600 atmos- 

 pheres. Absorption bands with centers at 6688, 6593, 4768, and 4687 

 were slightly intensified by pressure and the characteristic close 

 doublet which, according to Gibson, 19 has its components at 6943 and 

 6928 at room temperature and looks practically like a single band at 

 room temperature and normal pressure, is slightly sharpened by 

 pressure so that the components are more distinct and the band 

 appears to be shifted by a very small amount toward the violet. 



DuBois and Elias, 20 Mendenhall and Wood, 21 and Gibson 22 have 

 investigated the effect of decrease of temperature upon absorption in 

 the ruby and they all found the narrow red doublet to be sharpened 

 and more distinctly resolved. It is also shifted toward the violet 

 about 9 Angstroms with lowering of the temperature to —180 degrees. 

 Numerous absorption bands of wave-length between 6950 and 7100 

 were observed by DuBois and Elias and by Mendenhall and Wood at 

 liquid air temperatures. Gibson did not observe these bands but his 

 results show two bands at 5905 and 5965 breaking off from the broad 

 absorption band at these low temperatures and also a change in the 

 position of the maximum of this absorption band. 



17 Gibbs, Phvs. Rev., Vol. 31, p. 463, 1910. 



18 Gibson, Phys. Rev., Vol. 7, p. 194, 1916. 



19 Gibson, Phvs. Rev., Vol. 8, p. 38, 1916. 



20 Du Bois and Elias, Ann der Phvs., Vol. 27, p. 233; Vol. 35, p. 617. 



21 Mendenhall and Wood, Phil. Mag., Vol. 30, p. 316. 



22 Gibson, Phys. Rev., Vol. 8, p. 38. 



