394 - Scientific Intelligence. 



similar to the mixtures contained in natural juices, cause the 

 inversion of cane sugar far more slowly than the free acids alone 

 at the same concentration. — Comptes Rendus, 171, 316. 



h. l. w. 



6. The Einstein Displacement of Solar Lines. — As is now 

 well-known, there are three consequences of Einstein's theory 

 which are amenable to experimental observation or investigation, 

 namely: (a) the motion of the perihelion of the orbit of the 

 planet Mercmy, (b) the apparent displacement of the positions 

 of the stars on the celestial sphere due to the passage of the light 

 from the stars through the gravitational field of the sun, and (c) 

 the displacement toward longer wave-lengths of spectral lines 

 radiated near the edge or "limb" of the sun. The first two 

 predictions seem to have been fulfilled quantitatively as well as 

 qualitatively, but the third deduction from theory seemingly was 

 not verified by the earlier spectroscopic observations. 



The second paper by L. G-rebe and A. Bachem seems to remove 

 the last practical objection to Einstein's theory of gravitation. 

 The first part of the paper deals with the spurious photographic 

 displacements arising from the juxtaposition of partially or com- 

 pletely unresolved emission or absorption lines. By making a 

 careful microphotometric study of three spectrograms of the 

 solar absorption lines, — the source of which is now ascribed to 

 nitrogen, — the authors were able to select nine lines in the ultra 

 violet that are free from the contaminating influence of super- 

 posed lines of metallic origin. The wave-lengths of these nine 

 lines range from 3844.378A to 3873.504A. 



Expressed in terms of the equivalent Doppler effect, the final 

 result was that the displacement amounted to 0.56 kilometers 

 per second. This agrees with the value predicted by Einstein's 

 theory, 0.6 km. per sec, within the limits of error of the calcula- 

 tion. By way of comparison, the authors quote the following 

 data for such lines as were previously investigated by other 

 observers and which pertained to the same list of nine lines. 

 Schwarzschild (7 lines) 0.63; St. John (5 lines) 0.32; Evershed 

 and Royds (2 lines) 0.67. The weighted mean of all four data 

 is 0.54 km. per sec, which is as close to Einstein's datum as may 

 be expected at this immediate time. The least and the greatest 

 displacements obtained for different lines by Grebe and Bachem 

 were 0.3 and 1.2 respectively. All of the displacements were 

 toward the red. It appears, therefore, that the discordant and 

 non-confirmatory results published heretofore were due to the 

 inclusion of lines the positions of which were seriously influenced 

 by the superposition of adjacent metallic lines. — Ztschr. f. 

 Physik, 1, 51, 1920. h. s. u. 



7. Practical Physics; by Robert Andrews Millikan and 

 Henry Gordon Gale. Pp. x, 462, with 476 figures. Boston, 

 1920 (Ginn and Co.). — This volume is a revision of the authors' 

 "A First Course in Physics" carried out in collaboration with 

 Willard R. Pyle. (See 36, 423, 1913.) In many respects this 



