VIII. MEASUREMENT. 333 



a galvanometer, by Gourjon (the property of Sir C. Wheatstone) ; a dis- 

 charger, or spark measurer ; arid a Beiinet's gold-leaf electroscope. 



Continued regular observations were made with these instruments for several 

 years. 



The wooden stand now exhibited was not the original table upon which 

 they were placed ; that, a fixture in the Observatory, having been destroyed. 



The Henley electrometer has also been replaced by a less perfect instru- 

 ment. 



1433a. Box Electroscope, avoiding the faults of common 

 gold leaf electroscopes. Prof. Beetz, Munich. 



1433b. Bifilar Electroscope, with copper, zinc, and con- 

 denser-plates for showing Volta's fundamental experiments, and 

 tourmaline for showing pyro-electricity. Prof. Beetz, Munich. 



1434. Thomson's Divided King Electrometer and 

 Gauge, formerly in use for recording atmospheric electricity, at 

 the Kew Observatory. 



Kew Committee of the Royal Society. 



This instrument, which consists of two parts, the electrometer and the 

 gauge, was erected at the Kew Observatory in 1861, in connexion with a 

 photographic recording apparatus, and worked there for about four years, 

 producing .daily records of the fluctuations, &c. of atmospheric electricity, 

 which were discussed by Professor Everett, and the results published, together 

 with a description of the instrument, in the Philosophical Transactions for 

 1868, Pt. I. 



It has since been replaced by an improved quadrant electrometer. 



1435. Singer's Gold Leaf Electroscope, for lecture pur- 

 poses. Large size. Elliott Brothers. 



1436. Quadrant Electrometer, being a modification of Sir 

 W. Thomson's delicate quadrant electrometer, used for measuring 

 the difference of potential between two conductors. 



Elliott Brothers. 



1437. Peltier Electrometer, for measuring the electrical 

 tension of a charge by the repulsion of a light aluminium needle, 

 which receives a directive force from a very small magnet 

 attached to it. Elliott Brothers* 



1437a. Peltier Electrometer. 



The British Telegraph Manufactory, Limited. 



1438. Capillary Electrometer, after Lippmann. 



R. Jung, Heidelberg* 



A glass tube a, filled to a height of about 85 cent, with mercury, and 

 ending below in a fine point, dips in a cylinder b, so that its point presses 

 lightly against the side, where there is a microscope c placed horizontally. 

 The bottom of the cylinder contains mercury, and above this there is dilute 

 sulphuric acid which covers the point of the tube ; a platinum wire, con- 

 nected with one terminal of the apparatus and protected by a glass tube from 



