Chemistry and Physics. 479 



through ordinary filter paper to remove solid carbonic acid, re- 

 mains quite tranquil and beautifully transparent of a pale blue 

 tint." Liquid oxygen gave //= 1*226. Liquid nitrogen at —190° C. 

 and at atmospheric pressure gave for the D line /,i= 1*2053. Liquid 

 air gave for the D ray // = 1*2062. When certain proportions of 

 nitrogen had evaporated from the liquid air results were obtained 

 as follows: /* = 1-215, /< = 1*218.— Phil. Mag., October, 1893, pp. 

 328-331. j. t. 



9. Rotation air Pump. — Sprengel's pump and Geissler's pump 

 are the forms of pumps which are used for obtaining high vacua. 

 F. Schulze Berge has invented a new form which combines the 

 possibility of obtaining a high vacuum with a speed which com- 

 pares with that of a mechanical air pump. Vacua have been ob- 

 tained by this pump which are beyond accurate measurement on 

 McLeod's gauge. Several forms of the new pump are given by 

 the author. — Ann. cler Physik und Chemie, No. 10, 1893, p. 368- 

 376. J. t. 



10. Waves in air. — A. Raps has employed Jamin's interferential 

 refractor to study the rarefaction and condensation of air while 

 transmitting sound waves. One rav of light is led through air at 

 rest and the other is passed through the air which is in movement. 

 The two rays give interference fringes. These are received 

 through a suitable slit on a revolving cylinder which is covered 

 with photographic paper. The difference in the air paths thus 

 produce vibrating fringes. A spot on a dark fringe and a spot on 

 a bright fringe produce wave- shaped curves which represent 

 the movements of the vibrating air column. In this way the 

 author studies the movement of air in organ pipes and the move- 

 ment of sound waves in open air. A large number of photo- 

 graphic plates accompany this article. — Ann. cler P/iysik and 

 ^Ghemie, No. 10, 1893, pp. 194-220. J. t. 



11. Standards of low Electrical Resistance. — At the late meet- 

 ing of the British Association at Nottingham, Principal Jones de- 

 scribed a method of determining small resistances which is based 

 upon the Lorenz method of determining this ohm. The method 

 consists in rapidly rotating a copper disc whose center is on and 

 whose rotating axis coincides with the axis of a coil. The same 

 current is led through the coil and the resistance to be measured. 

 The difference of potential between the center and circumference 

 of the rotating disc is made to counterbalance that at the ends of 

 the resistance to be measured. A series of experiments on a re- 

 sistance of ao * 00 of an ohm was given and it showed that the 

 variation from the mean of the extreme values was 1 in 12,000. 



J. T. 



12. Equipotential and magnetic force-lines. — E. von Lommel 

 return? to a discussion of his explanation of the Hall effect. He 

 gives several plates of the distribution of magnetic filings upon 

 plates of various forms through which powerful currents are led 

 and compares these figures with representations of equipotential 

 lines and magnetic lines on similar formed plates given by Quincke 



