摘要:

A shielded conductivity bridge employing direct balance to ground and variable ratio arms is described. The bridge as a whole is probably capable of an accuracy of about 0.01 percent over a range of one million ohms with greater flexibility than that of the customary fixed ratio‐arm conductivity bridge. The range may be extended to ten million ohms with only slight loss in precision. By using the two extra ratios provided in the ground arms the resistance of all solvents except those of lowest dielectric constant may be measured to a few percent on the same bridge.

ISSN:0034-6748    

DOI:10.1063/1.1770076

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

The design and construction details for making a cold cathode x‐ray diffraction tube are included. A metal bellows incorporated in the cathode assembly permits adjustment of the cathode‐target distance. Vertical fins provide adequate cooling without forced draft and a simple target sealing assembly permits rapid interchange of targets.

ISSN:0034-6748    

DOI:10.1063/1.1770085

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

In the Apiezon oil McLeod gauge, the reservoir is in gas communication with the bulb, and the oil is displaced by a plunger externally controlled. The bulb has a volume of 300 cc, and the capillaries have a bore diameter of 1.44 mm. There is no evidence of sticking in the capillaries. For single measurements at pressures of 10−3, 10−4, 10−5, and 10−6mm of mercury the gauge is considered accurate to about 1, 2, 8, and 25 percent, respectively. The equivalent compression ratio for the gauge is 3.5×10−7. To degas the oil it is necessary to raise it about five times, for half‐hour periods, to the freely vaporizing state while the diffusion pumps are in operation. The whole instrument is kept continuously at a low pressure (10−2mm of mercury or less), thus enabling it to be used, at intervals of several months, without further heat treatment, for the measurement of pressure within its range.

ISSN:0034-6748    

DOI:10.1063/1.1770086

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

A study of the Barth balanced circuit employing the FP‐54 electrometer tube disclosed several new properties of the circuit. (1) The value of the filament current at which a balance is obtained usually shifts when the potential of the control grid is changed, thus throwing the circuit out of balance. This shift may be eliminated by suitable adjustments of the circuit resistances. (2) A balance usually exists at two or more values of the filament current, and these may be moved together by adjusting the circuit resistances so as to form a broad plateau. (3) Tubes with low plate current were difficult to balance until after their plate current was increased by ``flashing.'' The new balance, necessitating changes in circuit resistances, resulted in an increased range of balance.

ISSN:0034-6748    

DOI:10.1063/1.1770077

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

The use of stroboscopic patterns for fixing and measuring rotational speeds is discussed. Patterns having as many as nine bands may be utilized. The patterns occur in a definite recurring sequence, according to a simple numerical relation. Most of the speeds intermediate to those at which patterns are stationary may be obtained by correcting for the precession or recession of the patterns.

ISSN:0034-6748    

DOI:10.1063/1.1770078

出版商:AIP    

年代:1943

数据来源: AIP

摘要:

Methods and instruments to produce minute spots of ultraviolet light to realize selective irradiation of chromatin in living cells are discussed theoretically and checked experimentally. Two methods were developed: (1) lens method (focusing of ultraviolet light by means of quartz or fluorite lens), and (2) screen method (screening of ultraviolet light by means of a screen with minute opening). While the diffraction phenomena restrict the lower limit of the size of the irradiated spot, yet a spot as minute as 0.2&mgr; in diameter with the lens method, and 1&mgr; in diameter with the screen method, is obtainable. Biological material suitable for experimentation (certain protozoa, spermatozoa) is discussed briefly.

ISSN:0034-6748    

DOI:10.1063/1.1770079

出版商:AIP    

年代:1943

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1770080

出版商:AIP    

年代:1943

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1770081

出版商:AIP    

年代:1943

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1770082

出版商:AIP    

年代:1943

数据来源: AIP

ISSN:0034-6748    

DOI:10.1063/1.1770083

出版商:AIP    

年代:1943

数据来源: AIP