IX. RESISTANCE. 295 



d. VOLTAMETERS. 



1486. Voltameter. 



Geneva Association for Constructing Scientific Instru- 

 ments. 



The tube of the voltameter is divided on glass into sixteenths of cubic 

 centimetres. 



148 6 a. Voltameter for teaching. 



Physical Institute ( Univ. of Giessen), Dr. Buff. 



This apparatus for the decomposition of water is described in Liebig's 

 Annalen, Vol. 93, p. -256. It is intended to render the gases evolved 

 available for analysis or otherwise. 



The connecting piece, fitted above with caoutchouc tubing, serves for 

 ordinary purposes. By means of the apparatus, not only may the reconstitu- 

 tion of water be shown, but pretty intense phenomena of heating and ignition, 

 e.g., of a steel spring. For such experiments 12 Bunsen pairs are necessary, 

 connected in series. 



1486b. A Silver Voltameter, with platinum vessel. 



Prof. Beetz, Munchen. 

 A convenient modification of the Poggendorff voltameter. 



1486c. Mercury Voltameter. 



The Physical Science Laboratory of the Technological 

 Institute at St. Petersburg (Russia). 



This apparatus is intended for measuring the strength of currents by the 

 reduction of mercury. It consists of two electrolytic glass bowls joined by a 

 pipe, and an apparatus for measuring the reduced mercury volumetrically. 

 A more detailed description, with drawing and directions for use, accompany 

 the instrument. 



IX. APPARATUS FOR MEASURING ELECTRICAL 

 RESISTANCE AND CAPACITY. 



1487. Wheatstone's Bridge of the simplest construction, 

 'especially used for conductivity and low resistance tests. The 

 bridge is provided with one pair of equal resistances and one 

 standard resistance. Elliott Brothers. 



1488. Thomson's Circular Sliding Resistance, of greatest 

 importance in cable tests in connexion with the quadrant elec- 

 trometer for measuring resistance, tension, or potential of cables 

 and batteries, and for detecting faults in cables. 



Elliott Brothers. 



Megohm or 1 million Ohms resistance is indispensable for measuring very 

 high resistances, for determining the constant of galvanometers, &c. 



1489. Plate, showing Dr. Bosscha's Method of determin- 

 ing the Ratio of two resistances, with explanatory note. 



T. Bosscha, Professor, Royal Polytechnic School, Delft. 



