32 



Dr. G. Gore. 



[Dec. 18, 



In connexion with my present line of work I have had to retnrn to 

 the spectrnm of hydrogen, and I have photographed it, using an end- 

 on tube, which I owe to the kindness of Dr. Monkhoven, whose device 

 it is.* In the spectrum of the Monkhoven tube h is very well seen, 

 though not so strong as the line near Gr. 



What I wish, however, to draw special attention to now, is the fact 

 that other lines more refrangible are seen ; in the photographs I have 

 obtained, one of them, within the limits of dispersion that I have 

 employed (one dense prism of 60°, collimator 18 inches, and a small 

 Dalmeyer rectilinear lens in the camera), is coincident with a line 

 observed in the spectrum of calcium at X 3968*0 (H). 



More photographs are required to enable me to give the approximate 

 positions of the other lines more refrangible. 



VI. " On the Capillary Electroscope." By G. Gore, LL.D., 

 F.R.S. Received December 6, 1879. 



The following research was commenced with the hope of being able 

 to make an exact measuring instrument of a modified form which I 

 had devised (see page 37) of the " Capillary Electroscope," and to 

 employ it for the determination of the different degrees of electro- 

 motive force of different metals in forming tables of electro- chemical 

 series, with different electrolytic solutions. f With this object in view, 

 1 constructed and tried a considerable number of forms of the instru- 

 ment ; and employed a number of liquids, acid, neutral, and alkaline, 

 as conducting media between the mercurial electrodes. In every case, 

 however, an obstacle to uniform and accurate measurement sooner or 

 later arose, viz., unequal adhesion of the mercury to different parts of 

 the capillary tube. 



It has been noticed by other investigators that the motion of the 

 slender column of mercury in Lippmann's " Capillary Electrometer" 

 suddenly stops whilst under the electric influence, and this has been 

 supposed to increase the value of the instrument by rendering its 

 indications sensibly instantaneous. According to Lippmann also 

 " when the circuit was closed" by a metallic conductor, "all irregu- 

 larities at once disappeared" ("Phil. Mag.," April, 1874, p. 284). 

 This sudden stoppage of the mercury, however, whilst under the in- 

 fluence of the current is, I believe, in every case due to a sudden 

 increase of mechanical resistance, usually caused by unequal adhesion 



* It is right to add, however, that this form of tube also suggested itself to Pro- 

 fessor Piazzi Smyth quite independently. 



f See " On the Chemico-Electric Relations of Metals in Solutions of Salts of 

 Potassium." 



