258 SEC. 10. ELECTRICITY. 



1235a. Apparatus for uniting several Galvanic Elements 



into one of large surface, so as to preserve the entire strength of 

 the current by lessening the resistance. 



Imperial University of St. Petersburg. 



To effect this, two metal cylinders, each bored with seven holes parallel to 

 the axle, and fitted with screws, are used. In one cylinder, the six ends of 

 conductors directed by the positive electrodes (anodes) of the elements are 

 inserted, and in the other, the six conductors direct by the negative electrodes 

 (cathodes). The seventh hole is reserved for the conductor, the section of 

 which is equal to the total section of the six other conductors. This last 

 conductor issues from the side opposite to the cylinders. The apparatus here 

 described is used by Mr. Petroucheffsky in St. Petersburg. 



1235b. Large-sized Galvanometer, for demonstrating the 

 principal effects 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 quantities). Another ring, with more than 400 rounds of wire, serves 

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

 are united together, and can be set in the very differential pointings of the 

 hand which moves on a pivot at the centre of the cylinder, the lateral surface 

 of which is divided into degrees. The hand is furnished with two wires 

 crossing each other at right angles ; the four curved ends show the divisions 

 of the cylinder. 



This apparatus, for demonstration, is constructed according to the directions 

 of Mr. Petroucheffsky, Professor in the University of St. Petersburg. 



1235c. Apparatus intended for producing Thermo-electric 

 Currents in a special manner. 



Imperial University of St. Petersburg. 



It consists of ten direct electro-magnets, joined at their curved ends, the 

 whole forming a zig-zag. The iron blades do not touch closely, but are con- 

 nected by small brass cylinders to which they are soldered at their extremities. 

 These small cylinders carry brass plates and rods placed alternately. When 

 the apparatus is to be used, these plates are heated approximately up to 100 

 centigrade ; the brass rods are cooled with crushed ice, and then the galvanic 

 current of a six element battery (carbon, zinc, chromic liquid,) is inducted 

 into the bobbins of the electro-magnets, odd or even numbers. The thermo- 

 electric current thrown into the iron blades produces a strong deviation of 

 the hand of a sensitive galvanometer, and of the wires of small resisting 

 power. 



The fact of the heterogeneousness of magnetised metals and non-magnetised 

 metals was discovered by Mr. Thompson. The apparatus here described is 

 constructed by Mr. T. Petroucheffsky, Professor in the University of St. 

 Petersburg. The first experiments made with this apparatus, slightly altered 

 however, have been briefly described in Russian in the " Journal of the Russian 

 " Society of Chemistry," and in that of " The Physical Society of the Univer- 

 sity of St. Petersburg," Vol. 6, Section Phys., p. 107 (1874). 



1236. Holtz's Machine. Frederick Guthrie, F.R.S. 



A good example of this machine in one of its original forms, with window 

 and armatures. It gives a current of sparks over an interval of 8 inches. 



