490 BELL SYSTEM TECHNICAL JOURNAL 



This paper describes briefly the voltage and current relations, pre- 

 liminary tests on a small-scale rectifier, the phase shifting transformers 

 and their application to this particular situation, and presents data to 

 indicate their effectiveness. 



A New Quartz-Crystal Plate, Designated the GT, which Produces a 

 Very Constant Frequency over a Wide Temperature Range.^ W. P. 

 Mason. In this paper, a new quartz-crystal plate, designated the GT, 

 is described which produces a very constant frequency over a wide 

 temperature range. This crystal does not change by more than one 

 part in a million over a 100-degree centigrade range of temperature. 

 This crystal obtains its great temperature stability from the fact that 

 both the first and second derivatives of the frequency by the tempera- 

 ture are zero. Both the frequency and the temperature coefficient can 

 be independently adjusted. 



This crystal has been applied in frequency standards. In very precise 

 oscillators, and in filters subject to large temperature variations. It 

 has given a constancy of frequency considerably in excess of that ob- 

 tained by any other crystal. A crystal chronometer, using this type 

 of crystal, was recently lent to the Geophysical Union for measure- 

 ments on the variation of gravity and the chronometer is reported to 

 have kept time within several parts in 10 million, although no tempera- 

 ture control was used. 



Room Noise at Telephone Locations — //.^ D. F. Seacord. Room- 

 noise data, based primarily on measurements made at about 900 loca- 

 tions in and around Philadelphia and Chicago under winter conditions, 

 were reported informally to the conference on sound at the 1939 

 A. I. E. E. winter convention. The present article supplements the 

 earlier material and includes a summary of room-noise conditions ex- 

 pressed in terms of annual averages based on both the winter survey 

 data previously discussed and the summer survey data that had been 

 obtained at about 1,300 locations but had not been completely analyzed 

 at the time of the earlier report. The summer survey included 500 

 measurements at locations previously measured during the winter in 

 and around Philadelphia and Chicago, and 800 measurements at loca- 

 tions in and around Cleveland, New York City, northern New Jersey, 

 and Philadelphia. Annual average as used in this article is the mean 

 of winter and summer measurements. In addition, the present article 

 includes a brief discussion of outdoor noise and the relative frequency 

 of occurrence of several predominant sources of room noise. 



3 Proc. I. R. E., May 1940. 

 ^ Elec. Engg., June 1940. 



