ISSN:0034-6748    

DOI:10.1063/1.1751582

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

An integrating sphere type of physical densitometer has been developed with a view to standardizing density measurements in the motion picture industry. The instrument accommodates films or plates up to 5″ wide. Scanning beam dimensions of 0.025″×0.100″ are used but may readily be changed. Density values corresponding to (1) the equivalent of standard visual diffuse or (2) photographic printing density may be obtained by insertion of suitable optical filters. Densities up to 3.0 are read directly on a special three‐scale logarithmic meter which provides a uniform density scale. A chopper in the light path makes possible a.c. amplification using a highly stabilized amplifier with a highly selective gain‐frequency characteristic. This latter feature permits operation in daylight or in a room illuminated with ordinary a.c. lamps. Calibration is based on the inverse square law.

ISSN:0034-6748    

DOI:10.1063/1.1751583

出版商:AIP    

年代:1940

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1751584

出版商:AIP    

年代:1940

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1751585

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

Transmissions and reflections have been measured at nine wave‐lengths between 20.7&mgr; and 152&mgr; for a number of plastics and special surfaces. The residual rays from crystals were used as sources of approximately monochromatic radiation. The general purpose of the investigation is to find materials for absorbing and transmitting filters to be used in the far infra‐red region of the spectrum. The spectroscopy of the far infra‐red depends primarily upon the use of absorbing filters and reflecting surfaces to obtain purity of spectra. Relatively few materials are suitable for these purposes and additional materials are greatly needed. Vacuum spectrographs and absorption cells require transparent windows capable of standing pressure. It is difficult to avoid using less than four such windows in any spectroscopic arrangement. If the transmission of the individual windows can be raised from 60 percent to 80 percent the transmission of the four is increased by a factor of more than three. Similarly it is a matter of importance that the absorbing material on the receiving surfaces of the thermopile be efficient in transforming incident radiant energy into heat. The satisfactory solution of these technical requirements in the far infra‐red is a much more difficult one than in the near infra‐red, with the result that extended investigations to discover materials suitable for these various purposes cannot well be avoided. The results recorded here deal primarily with plastics though a number of other substances are included.

ISSN:0034-6748    

DOI:10.1063/1.1751586

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

Three methods are described for the generation of alternating voltages having a square‐wave shape and covering a wide range of frequencies. The first method is based on a previously developed system and uses an overloaded direct‐coupled degenerative vacuum‐tube amplifier. The second method uses a special pulse generator followed by a vacuum‐tube trigger circuit. The third method is a combination of the first two and produces waves which are squarer than those produced by the individual systems. Very square waves are obtained with all systems at frequencies up to 200 kilocycles per second and with loading capacities up to 100 micromicrofarads. The applications of these waves are considered, as well as the importance of the circuits for other purposes. Of special interest are the suggested improvements in conventional ``scale‐of‐two'' counting circuits and the description of the high frequency pulsing circuit.

ISSN:0034-6748    

DOI:10.1063/1.1751587

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

When observing voltages in high impedance circuits by means of an ordinary cathode‐ray oscilloscope, one often encounters disturbance of circuit conditions by the relatively low impedance to ground of one of the oscilloscope amplifier input terminals. The authors present a coupling circuit for eliminating this difficulty in which the voltage to be observed modulates an oscillator isolated from ground. The resulting output is loosely coupled to a detector built into the oscilloscope. The paper shows that the system not only fulfills its purpose and indicates wave forms correctly, but is also economical and easily adjusted.

ISSN:0034-6748    

DOI:10.1063/1.1751588

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

Fused quartz membrane manometers, used as null instruments, have been developed for measuring pressures of Hg, or other vapors (or gases) from a few centimeters of Hg to 50 atmospheres, with an accuracy of the order of 0.1 percent. The membranes are clear fused quartz disks, plane polished, 0.1 to 0.5 mm in thickness, and 0.5 cm to 2.5 cm in diameter. These are sealed onto fused quartz heads, either plane or slightly concave. In the first case, the motions of the diaphragms are magnified mechanically by a three‐legged rocker, the two outer legs of which rest on fixed bearings and the middle one of which rests on the diaphragm. The three legs being only slightly out of line, a high magnification (up to 6000) is obtained when a mirror and a long light path are used, or a pointer and a microscope are employed. In the second case, interference fringes set up between the diaphragm and the near‐by slightly concave quartz surface indicate the motions of the former. Volumes as small as 4 mm3have been attained, and all‐quartz manometers, remarkably constant in calibration, are operable at temperatures of 800°C, or higher. Certain forms of these manometers are extremely rugged and free from explosion hazard at high pressures. These manometers are being used to measure the operating pressures in high pressure (H‐type) Hg lamps.

ISSN:0034-6748    

DOI:10.1063/1.1751589

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

In this paper a direct‐current amplifier is described which employs negative feedback for the measurement of small stellar photoelectric currents. A General Electric type FP‐54 electrometer tube is used in the input stage to give maximum sensitivity. The output voltage is fed back negatively into the input stage and the amplifier locks in a condition of equilibrium. In this condition the output voltage matches the input voltage with a tenacity proportional to the voltage gain of the amplifier before the feedback is applied. A high gain stage employing one type 1N5‐G tube as a load for another type 1N5‐G tube supplies a voltage gain of about 1500. The output stage uses a type 1C5‐G tube connected as a triode. The output meter used is a Weston portable microammeter with full scale deflection of 50 microamperes. A 1900‐ohm resistance is used in series with the meter to give full scale deflection for 0.1 volt. Thus with an input resistance of 2×1010ohms, a photoelectric current of 5×10−12ampere gives full scale deflection.

ISSN:0034-6748    

DOI:10.1063/1.1751590

出版商:AIP    

年代:1940

数据来源: AIP

摘要:

An improved apparatus for the direct measurement of the absorption of sound in gases has been designed, built, and tested with the highly absorptive gases, carbon dioxide and nitrous oxide. Measurements are made of the sound pressure by a microphone as it is moved away from a piston source vibrating in a large baffle. The resulting pressure‐distance curves are recorded photographically and yield the absorption coefficient. Reflections from the walls of the cylindrical measuring chamber are reduced materially by specially designed glass baffles. The source is the end of a magnetostrictive rod driven by an improved Pierce‐type oscillator with a frequency range of 11.3 to 112 kc. A magnetic drive is employed to move the microphone, eliminating packing glands and providing a constant volume measuring chamber. The microphone was built up from a single bender‐type Rochelle salt bimorph element. A milliampere meter movement is used in the recorder, making possible comparatively rapid recordings.

ISSN:0034-6748    

DOI:10.1063/1.1751591

出版商:AIP    

年代:1940

数据来源: AIP