685 



support the apparatus. Here follows a more detailed description of 

 the arrangement ^) *). 



Description of the apparatus: 



It is illustrated by the following reproductions: 



Fig. 2 has been taken from a photo representing the apparatus 

 as if seen somewhat from the top. 



Fig. 3 is a vertical section through the plaae of one of the rods, 

 viz: the capacity rod /,, while Fig. 4 shows the ebonite disc in 

 horizontal section, the two last being at a third of tlieir real size. 



Starting from the central part of the apparatus we shall find that 

 the needle d is exactly in ihe middle; it is made of platinum and 

 consists of two parts, the lower part of which slides tightly 

 into the upper; in the middle this upper part is surrounded by a 

 very small cylinder, which contains two small cavities in order to 

 promote the good contact of the needle with the two rods which 

 touch it on two sides; viz. the charging rod /, and the capacity 

 rod 4. (Of. Figures 3 and 4). The needle (/ is insulated by ambroid 

 (dotted in Fig. 3) which consists of two cylindriform pieces, to the 

 lower of which the needle is fastened, while the upper part, provided 

 with two wide perforations for the rods, enclose the needle loosely. 

 The ambroid is entirely surrounded by a brass tube serving as 

 guardring, in ordei- to prevent loss of charge of the needle as well 

 as electrostatic distuibances upon it. This tube also consists of tw^o 

 parts : of a small lower cylinder with a thick outer rim at the bottom 

 containing screw-perforations (in Fig. 4 : 1) by means of which the 

 guardring with the ambroid and the needle can be fastened to the 

 surrounding ebonite plate. The lower cylinder fits loosely in the 

 excavation of the ebonite and slides tightly in the upper part of 

 the guardring, which, besides two wide perforations for the rods 

 /, and /,, is yet provided with a screw-perforation for the third rod 

 /,, which brings the guardring to the potential value desired. (Cf. 

 Fig. 4). The ebonite plate itself is fastened to the lower side of the 

 brass bottom plate i of the measuring space c by means of three 

 brass screws and nuts (Fig. 4:2; Fig. 3 : the screws to the left of 



1) The electrometer was constructed in the workshop of the Physical Laboratory 

 at Groningen by Mr. H. J. Sips, who, with great devotion, surmounted in such a 

 masterly way the many difficulties which arose when he performed his task. 



Mr. D. A. VoNK, as chief of the workshop, in many respects gave also valuable 

 indications. 



^) The Instrument-Manufacture and Trade late of P. J. Kipp and Sons, (lim.) 

 Delft (Holland) is willing to construct the apparatus described here on sufficient 

 demand. 



