334 SEC. 10. ELECTRICITY. 



the sulphuric acid, dips into the mercury. The long tube is connected above 

 with a small glass inverted U-tube, in which a platinum wire is fused, which, 

 reaching down into the mercury in the tube, forms the upper electrode. The 

 other end of the U-tube is connected by caoutchouc tubing with au air press, 

 which, on its other side, is connected with a manometer. A little mercury is 

 first forced through the fine point by means of the press. The microscope is 

 then so placed that the zero point of the eyepiece micrometer coincides with 

 the image of the meniscus of mercury in the capillary tube ; then the electric 

 source to be measured is brought into the circuit of the apparatus, its negative 

 pole being connected with the upper electrode. The mercury forthwith 

 retires, and can only be brought back by a determinate pressure with the 

 press. 



1439. Coulomb's Torsion Balance, for measuring mag- 

 netic and electric attraction and repulsion. Elliott Brothers. 



1439a. School Form of Coulomb's Torsion Balance. 



Harvey, Reynolds, and Co. 



b. GALVANOMETERS. 



61. Galvanometer for hydro-electrical currents, with which 

 Matteucci discovered, in 1844, the muscular current. 



The Royal Institute of " Studii Superiori " at Florence. 



The Copley medal was awarded by the Royal Society to Matteucci for his 

 electro-physiological labours, and above all for his discovery of the muscular 

 current. 



Galvanometer of Nobili, with astatic system, and bobbin 

 composed of eight threads to be united at pleasure. 



The Royal Institute of " Studii Superiori '' at Florence. 



Galvanometer of Nobili, with astatic system for the hydro- 

 electrical current. 



The Royal Institute of " Studii Superiori " at Florence. 



56. Magnetoscope of Nobili, composed of an astatic system 

 suspended in a glass bell furnished with a graduated circle. 



The Royal Institute of " Studii Superiori " at Florence. 



The first galvanometer upon the astatic system was made by Nobili, in 

 1825. He afterwards so improved galvanometers, that they could be adapted 

 to every kind of current, and be perfectly similar to one another. As to 

 the magnetoscope, he made use of it to detect the slightest traces of 

 magnetism. 



1235b. Large-sized Galvanometer, for demonstrating the 

 principal applications of Ohm's formula. 



Imperial University of St. Petersburg. 



It consists of a strong brass ring, below which are two long plates, fitted at 

 their extremities with an adjustment for uniting the galvanic couples parallel- 

 wise (in quantity). Another ring, with more than 400 turns of wire, serves to 

 study the combination of the couples in a different way. The two rings are 

 united together, and can be set different distances from the needle. The 



