394: Scientific Intelligence. 



original paper is accompanied by a plate showing photographs 

 of the bands obtained in white, in monochromatic violet, and in 

 filtered yellow light. 



With a specimen of quartz, which was apparently quite color- 

 less, it was not possible to observe the scattering visually, but 

 it was detected photographically. Intensity comparisons were 

 made between the total light scattered by clear quartz and by 

 certain other media. The following results were obtained : dust- 

 free air, 1 ; clear quartz, 8 ; plate glass, 300 ; liquid ether, 900. 

 "I have also observed a scattering strong compared with that of 

 air, in a rhomb of clear Iceland spar. No intensity measure- 

 ments were made." — Proc. Roy. Soc, 95 A, 476, 1919. 



h. s. u. 



6. Apparatus for the Direct Determination of Accelera- 

 tions. — The question of the determination of the acceleration of 

 the true motion of the ground in various seismic phenomena, or 

 of the motion in different parts of buildings, bridges, and all 

 kinds of artificial structures, due to explosions, shocks, or oscilla- 

 tions of the ground, has a considerable theoretical and practical 

 interest, since the investigation of these accelerations serves as a 

 guide in the study of the mechanical forces by which these move- 

 ments are caused. An assemblage of apparatus which fulfills 

 all the requirements of the problem has been ingeniously 

 designed and subsequently tested by the late B. Galitzin. The 

 essential parts of the apparatus, intended for the study of hori- 

 zontal movements only, will be described in the following 

 sentences. Obviously, the same principles may be applied to the 

 analysis of vertical movements. 



The base of the instrument proper consists of a horizontal 

 solid cast-iron platform which supports, and is rigidly attached 

 to, a prismatic mass of the same material. The cross-section of 

 the prism, in the plane of motion of the pendulum to be 

 described below, is a right triangle ABC. The short side BC 

 is horizontal and the long leg CA is vertical. At the upper ver- 

 tex A there juts out horizontally a short rigid projection which 

 supports a massive pendulum in such a manner as to permit free 

 motion only in the plane of the triangular vertical section of the 

 prismatic pillar. The pendulum is of the Borda type with a 

 rigid bar above the heavy bob. A pin is fastened to the bob on 

 the side nearest to CA. The axis of this pin passes through the 

 center of mass of the entire pendulum in a direction at right 

 angles to the long axis of the bar. When at rest, the bar makes 

 a small but finite angle a with the vertical, CA. Between the 

 face CA of the pillar and the nearer end of the pin, a little table 

 or platform is built out solidly on the pillar. This table sup- 

 ports a plane-parallel slab of quartz suitably cut with respect 

 to the crystallographic axes. The back of the slab makes good 

 contact with a solid wedge of triangular cross-section the upper 

 angle of which is equal to a. In other words, the front face of 



