ABSTRACTS OF TECHNICAL ARTICLES 527 



indicate that the matched impedance condition gives the best results 

 in practice. 



llie World's Most Pou'erful Microscope.' F. F. Lucas. In the last 

 ten years there has been developed at Bell Telephone Laboratories a 

 new technic of high-power micrography, which has greatly extended 

 the limits of useful magnification possible with a microscope. Since 

 any extension of the limits of magnification of the microscope which 

 is accompanied by a decrease in definition is useless, it was found 

 necessary to increase the resolving power or definition of the micro- 

 scope. One way in which this can be done is by decreasing the 

 wave length of the light used. 



A microscope using ultra-violet light was developed about thirty 

 years ago by Koehler of the Zeiss works. Due to various difificulties 

 in operating it, this microscope soon became a scientific curiosity and 

 was almost forgotten. About five years ago, a microscope of this 

 type was obtained from the Zeiss works by Bell Laboratories, and the 

 difificulties involved in the use of this instrument were largely solved 

 by the development of a mechanical method of focusing. With this 

 microscope, it is possible to obtain crisp, brilliant images of metal- 

 lurgical specimens magnified 5000 to 6000 diameters. In studying 

 the advantages and limitations of this microscope, it was found to be 

 particularly applicable to the study of biological and medical speci- 

 mens. Such specimens can be examined at high magnification under 

 the ultra-violet microscope without the necessity of cutting, staining, 

 or injuring them in any way. 



A Direct Reading Audio-Frequency Phase Meter. ^ W. R. MacLeax 

 and L. J. Siviax. In connection with certain acoustic studies it was 

 desired to measure sound pressures as vectors, i.e. to determine both 

 the amplitudes and the phase angles. An example, more fully de- 

 scribed at the end of the paper, is the measurement of the amplitude 

 and phase variations in the pressure at various points in a room 

 excited by a tone from a loudspeaker. If a microphone traverses a 

 path in the room the amplitude and phase changes in its output 

 voltage are equal to the corresponding changes in the sound pressure. 

 Thus, the measurement is reduced to an electrical one, except for the 

 absolute calibration of the microphone and associated electrical circuit. 

 At any one frequency, relative changes of amplitude and phase with 

 position usually are all that is of interest, in which case no calibration 

 is necessary. 



' Jour. S. M. p. E., April, 1931. 



^ Jour. Acous. Sac. of America, April, 1931. 



