282 CARNEGIE INSTITUTION OF WASHINGTON. 



placed mirrors, interference fringes are produced when the beams are 

 reunited after having traversed very nearly equal paths in opposite 

 directions. At the pole of the earth, and to a less degree at any other 

 latitude, in consequence of the earth's rotation, the time interval for 

 one of the pencils will be less than that for the other by an amount 

 depending on the area included within the circuit. At a latitude of 

 35° the retardation in light-waves, and therefore the displacement of 

 the fringes, will be of the order of one fringe per square kilometer 

 of area. This result follows from the general theory of relativity as 

 well as from the hypothesis of an ether fixed in space. 



Should the result of the experiment show such a displacement, no 

 decision could be reached. If, however, the displacement should be 

 zero, or appreciably less than the calculated amount, it would show 

 that the basis of the theory of relativity is incorrect and would prove 

 the existence of a medium (ether) which is not stationary but is dragged 

 along by the earth in its rotation either partially or completely. 



The first requirement of such an experiment is that the fringes be 

 visible over a very long path of light. With the apparatus set up on 

 Mount Wilson at distances up to 700 meters, Professor Michelson 

 found the fringes readily visible and measurable to within a few one- 

 hundredths of a fringe. With a considerably larger circuit, about 

 3,000 meters, the fringes could not be seen. The investigation will be 

 continued at the longest distances at which the fringes are visible. 



Assisting Professor Michelson in this experiment were Messrs. 

 Smith, Benioff, Richard Scares, and Drummond. 



MAJORANA'S ABSORPTION OF GRAVITATION. 



Majorana's theory of the absorption of gravitation in passing 

 through matter leads to consequences with regard to the motions of 

 the planets and the moon which are glaringly inconsistent with obser- 

 vation, unless it is assumed that the inertial mass, as well as the 

 gravitational force, is diminished by the "screening" influence, and 

 both in the same ratio. The phenomena of the tides show that, even 

 on this assumption, any absorption of the sun's gravitational force 

 within the body of the earth must be less than one five-thousandth 

 as great as Majorana supposes. 



Majorana's experiment (if the reality of the effect which he has 

 observed is confirmed) may be explained on the assumption that the 

 mass of a body (both inertial and gravitational) is diminished when 

 another large body is brought near it; but direct interposition between 

 the earth and the first body can not be essential for this effect. 



ACCURACY OF PARALLAX DETERMINATIONS. 



Formulae have been developed by Professor Russell showing the 

 accuracy with which the mean parallax of a group of stars can be found 

 from their parallactic and peculiar motions. If the mean peculiar 

 radial velocity of the stars is less than 14 km. sec, the parallactic 



