182 ANNUAL, REPORT SMITHSONIAN INSTITUTION, 1908. 



tion by merely opening a steam valve and has no complicated elec- 

 trical apparatus or circuits of anj^ kind. The speed is regulated by 

 the steam pressure, this being accomplished by an electrically operated 

 reducing valve. 



For measuring the frequency various speed indicators have been 

 tried, but it has been found that the best way is to use a resonant 

 circuit, with an ammeter (shown in plate 11) in it," this being an ex- 

 tremely sensitive means of indicating the frequency, and in addition 

 affording a means of automatically keeping the speed constant to a 

 small fraction of a per cent. The reducing valve is adjusted so that 

 if left to itself the machine will run slightly above speed.^ As soon 

 as it reaches one-tenth of 1 per cent higher than its designed speed, 

 the resonance begins to fall, and a contact is oj)ened which slightly 

 throttles the steam. In this way the frequency is kept varying be- 

 tween the limits of one-tenth of 1 per cent above speed and one- 

 tenth of 1 per cent below speed. Where the drive is electric instead 

 of by turbine, a storage battery is used to drive the two-phase gen- 

 erator, and even better results may be obtained as regards regulation 

 than with steam. 



Transmitters. 



The types of transmitters most commonly used are the carbon 

 transmitter and static transmitter, and the carbon transmitter relay. 



Plate 10, figure 2, shows the standard type of carbon transmitter. 



It was found that the ordinary carbon transmitter was unsuited 

 for wireless telephonic work, on account of its inability to handle 

 large amounts of power. A new type of transmitter was therefore 

 designed, which the writer has called the '' trough " transmitter. It 

 consists of a soapstone annulus to which are clamped two plates with 

 platinum-iridium electrodes. Through a hole in the center of one 

 plate passes a rod, attached at one end to a diaphragm and at the 

 other to a platinum-iridium spade. The two outside electrodes are 

 water jacketed. 



This transmitter requires no adjusting. All that is necessary is to 

 place a teaspoonful of carbon granules in the central space. It is 

 able to carry as much as 15 amperes continuously without the articu- 

 lation falling off appreciably. It has the advantage that it never 

 packs. The reason for this appears to be that when the carbon on 

 one side heats and expands the electrode is pushed over against the 

 carbon on the other side. These transmitters have handled amounts 

 of energy up to one-half horsepower, and under these circumstances 

 give remarkably clear and perfect articulation and may be left in 



" Electrical World and Engineer, November 11, 1899. 



* Since writing the above, my attention has been called to the fact that the 

 general method of governing by resonance was invented aod patented by Kemp- 

 ster B. Miller, United States patent No. 559187, February 25, 1896. 



