ABSTRACTS OF RTCIINI' ITCIIMCAI. PAPERS 525 



nia>- be mentioned the fact that the original picture, for instance a 

 photographic negative, is not seen by the ()i)eralor at the receiving 

 end. He cannot, therefore, by using his photographic knowledge and 

 experience, choose printing media and decide upon conditions of 

 exposure and development. As an illustration of the opportunities 

 introduced by an electrical picture transmission apparatus may be 

 noted the possibility of so poling the electrical elements that the 

 received picture may be either a positive or negative, irrespective 

 of the nature of the original at the sending end. 



While in other picture transmission systems other problems arise 

 peculiar to these systems, it is believed that although the questions 

 considered are those presented in commercial operation in the Bell 

 System, they are, to a certain extent, common to all electrical picture 

 transmission apparatus. 



A Radio Field-Strength Measuring System for Frequencies up to 

 Forty Megacycles.^ H. T. Friis and E. Bruce. In previous types 

 of radio field strength measurement apparatus it is very difBcult to 

 reproduce accurately the small comparison voltages at very high 

 frequencies, due to reactive effects in the attenuating networks. The 

 "tube voltmeter" is practically the only reliable instrument available 

 at high frequency measurement w'ork. New measurement sets for 

 very high frequency signals have, therefore, been developed. The 

 apparatus is a double detection receiving set which is equipped with a 

 calibrated intermediate frequency attenuator and a local signal 

 comparison oscillator. The local signal is measured by means of the 

 intermediate frequency detector which is calibrated as a tube volt- 

 meter and all required attenuations are made at the relativeh' low 

 and fixed intermediate frequency. 



A New Mechanical Test for Rubber Insulation.'^ C. L. Hippensteel. 

 This paper discusses the development of a rapid routine test which 

 will numerically express the ability of the rubber insulation to resist 

 cutting by the conductor at the points of support and to resist cracking 

 at points of extreme flexure. Up to the present time no one test of 

 that nature has been described. 



' Presented at a meeting of the Institute of Radio Engineers, May 5, 1926. 

 ^ Industrial and Engineering Chemistry, April, 1926. 



