316 W. P. White — Switch for Thermoelement Work. 



gases (except chlorine) are likely to be abundant, gold plating 

 might be very desirable. 



In order to provide for 16 connections it would be best to have 

 two operating rod frames, one on top of the other, two thermo- 

 element bus bars, and one more auxiliary-connecting frame. 



The auxiliary-connecting frames together constitute the 

 " master switch " for the potentiometer used. If this is a 

 combination potentiometer* another arrangement has consider- 

 able advantages, though details have not yet been worked out. 

 For it everything resembling a master switch is omitted, and 

 the 4 potentiometer dials are replaced by 40 strips of cop- 

 per, arranged in parallel lines running from the operator, 

 clamped by a series of wooden strips, insulated with celluloid 

 as in the switch. Above and at right angles to these are 

 several, perhaps 4, sets of contact makers, each consisting of 4 

 contact pieces sliding on a stout bar, or pair of bars, and per- 

 forming the functions of the arms of 4 dial switches. Each 

 auxiliary-connecting frame, when pushed back, depresses one 

 of the contact-making bars by means of a suitable connecting 

 mechanism, thus putting into action the particular dial setting 

 made upon that particular bar. This arrangement gives a 

 quadruple potentiometer more easily and cheaply than by a 

 series of dials, and is also more nearly neutral ; though it is not 

 quite so completely neutral as a Diesselhorst-Wolff poten- 

 tiometer. t 



Summary. 



A switch combination is described, intended to promote 

 rapidity (and, therefore, often accuracy also) in making com- 

 prehensive and varied measurements with potentiometers. . The 

 type is characterized by the use of contacts between thin copper 

 strips, which is, thermoelectrically, perhaps the best contact 

 obtainable. A new mechanical arrangement greatly promotes 

 convenience and flexibility in operation. Other schemes make 

 construction and overhauling extraordinarily easy. 



Geophysical Laboratory, 



Carnegie Institution of Washington, Jan. 25, 1916. 



* Potentiometers for Thermoelectric Measurements, etc., loc. cit., page 

 1874. 



f Diesselhorst. Instrumentenkunde, xxxiii, 1, 1908; Potentiometers for 

 Thermoelectric Measurements, etc., loc. cit., pp. 1871-73. 



