Experimental Switchboards and Experimental Resistances. General. 



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Experimental Switchboards and Experimental Resistances 

 for Educational Institutions and Laboratories. 



General. 



With the introduction of heavy currents of electricity for teaching purposes, the necessity 

 has arisen for an experimental switchboard in connection with which all experiments can be made 

 which were hitherto carried out in conjunction with galvanic batteries or accumulators. It must be 

 home in mind that most of the experimental electrical apparatus, especially in regard to the re-i- 

 tance conditions, are constructed in such manner that they can be worked with a few cells, and 



with a low voltage require a greater current intensity, 

 while the working voltage is as a rule 220 volts, or 

 in a number of cases, 110 volts. 



On the other hand, the switchboard should 

 permit of such experiments being made which are 

 only rendered possible by heavy currents, such as 

 the demonstration of the electric arc light, the singing 



arc. and others. 



The switchboard must accordingly be so con- 

 structed that on connecting up to a heavy current 

 network, work can be carried on with a low or a 

 high current intensity, as also at a high and a low 

 voltage. The last condition especially must be satis- 

 fied in the case of apparatus working with an inter- 

 rupted current, such as Ampere's table, the spark 

 coil with platinum interrupter, the electric bell, etc. 

 It must be observed that this is not realised simply 

 by inserting romances in series, since at the moment 

 of breaking the circuit the full network voltage would 

 prevail at the contacts, and the contacts themselves 

 become fused together. Bather must the voltage be 

 distributed by a shunt method of grouping so that 

 it is impossible for the voltage to exceed a certain 

 value. 



The switchboard must in addition be provided 

 with measuring instruments for the current and vol- 

 tage. In the case of the potential, it must be possible 

 to measure the voltage at the apparatus as well as 

 in the network; it is also desirable to measure both 

 the total current taken from the main and the current 

 consumed in the experimental apparatus alone. 



50471. 1 : 8. 



\\r have constructed a switchboard which entirely fulfils the conditions just prescribed and 

 permits of the carrying out of all experiments which may need to be conducted in teaching or in 

 the laboratory. We have already supplied this type of switchboard to a very large number of edu- 

 cational institutions, and they have met with universal approval, resulting in repeat orders being 

 received from a number of towns. The names of the institutions are appended at the end of this 

 section, together with some testimonials appreciative of our switchboards. 



A number of forms of switchboards are described yi the following pages partly from data 

 obtained from a study of the various voltage conditions and kinds of currents of electricity works 

 and partly as the result of the differing needs and means of the educational institutions. 



el. 47;;s. 



