308 REPOET— 1893. 



tion of the roller might also be increased, so as to give a more detailed 

 representation of the recorded movements. 



Combination of tivo Pendulums in Ferpendicular Planes. — The method 

 of arranging two pendulums in perpendicular planes is shown in fig. 9. 

 Ai and A2 are the pendulums in the planes of the meridian and prime 

 vertical respectively, Mj and Mg their mirrors. The light enters in the 

 direction of the dotted line through a lens of about 4 m. focal length 

 at B, and returns after reflection along the same course. Cj and C2 are 

 the correcting-mirrors of the two pendulums, D a fixed mirror at right 

 angles to the path of the light. All three mirrors can be rotated from 

 outside the apparatus about a vertical and horizontal axis, s, and Sj are 

 screws for the longitudinal correction of the lower steel points of the two 

 pendulums, Tj and T2 screws for the lateral correction of the upper steel 



points. The lamp and roller are, as 

 ^^' before, placed side by side. When the 



i — ; i — 3 ; — i apparatus is properly adjusted no cor- 



jcaUoTfase rections are necessary, except those 



required for the rotation of the correct- 

 ing-mirrors, in order to keep the points 

 of light on the middle of the roller. 



Combination of two Pendulums in 



the same Plane. — As already remarked, 



the length of the period of oscillation 



;'; ;! and consequently the sensitiveness of 



i ': ; ; the pendulum are limited by the diffi- 



j; I; culty of obtaining very fine steel points. 



i '; ; i By arranging two exactly similar pen- 



; i ■ '; dulums in one plane, as shown in fig. 



I ■ ;' ■ 10, we can obtain four times the exac- 



; : '■ \ titude of registration without increas- 



; i I : mg the sensitiveness of the pendulums. 



• I ; ■ A, and Aj are the pendulums, Mj and 



; '; i 1 M, their mirrors inclined at angles of 



;■ 1 ; ; 45° to the common axis of the pendu- 



1 1 ; 1 lums and at right angles to one 



; '; ; i another. The light passes through the 



i ! ; 1 slit, S, and after double reflection by 



j 1; '1 the mirrors, and refraction by the lens, 



i 1 ! B, forms two images at Cj and C2. If 



there be any change of level or of 

 the vertical in a direction inclined to the common axis of the pendulums, 

 both are equally deflected towards the same side of the axis. The angle 

 between the mirrors alters by double this deflection, and the distance 

 between the images Cj and C2 is four times as great as would be produced 

 by the employment of a single pendulum and fixed mirror. This greater 

 accuracy of registration would be of great advantage in investigations on 

 small movements such as are produced by the influence of the moon. 



Inst of Memoirs by Br. E. von Pebeur-Paschiciiz. — The following is a 

 list of memoirs published by Dr. von Rebeur Paschwitz on the horizontal 

 pendulum, and the results so far obtained with it : — 



1. ' Ueber das Zollner'sche Horizontalpendel nnd neue Versuche mit 



demselben,' 'Verb, des naturw. Ver. zu Karlsruhe,' Bd. x., 1887. 



2. ' Ueber einen Versuch, die Veranderungen der Horizontalebene mit Hiilfe 



