For small
volume aboratory work... Adams | Centrifuges • Taster Sedimentation—utilize angle principle • For micro and semi-micro work • Rheostats have "off" position for continuous speed control • Precision-machined heads for accurate balance • 2 models: Safety-Head for six 15-ml tubes; Safeguard Angle-Head for 12 15-ml tubes and nine interchangeable heads Write for Form 309 containing complete défaits.
fYankee I Shakers • Low form, compact design • Ball bearing moving parts • i y 2 " stroke-275-285 oscillations/min. • 2 0 " x 1 2 " x 8 " - P l a t f o r m size 12" χ 15" • Timed or continuous operation Form 505 has complete details.
Γ"
Yankee Rotators • Impart a gentle circular motion of % " diameter similar to hand rotation • Rubber-covered platforms • 1 1 " χ 1 1 " platform-130or 180 RPM • 2 to 5 minute timer with automatic cut-off Write for Form 501 for complete details.
Order from your dealer
INSTRUMENTATION, continued amplified output of which is presented on a large cathode ray tube. The sweep rates on both scanning tube and receiving tube are synchronized, so that the image on the viewing screen is a faithful copy of the specimen scanned. Some of the advantages of the flying spot microscope are: 1. The specimen can be viewed by large audiences simultaneouslj7 on one or a multiplicity of receiving tubes. 2. Contrast within the image of the specimen can be varied by electronic means; indeed, for those cases in which ultraviolet or near ultraviolet is used in the scanning source, it is possible to secure contrast even for specimens which are un stained. 3. In normal microscopic work, the use of high light intensities may damage or distort the specimen, whereas with the flying spot technique, although the peak intensity of the spot may be high, its speed is also high and therefore the aver age intensity is very low. In addition to these advantages, the equipment may also be used for auto matic or rapid counting and sorting. Magnetic
141 East 25th Street, New York 10, Ν . Υ.
34 A
Recording
The recording of information by mag netic pickups is a half century old, but only one principle of reproduction has been employed. This is the generation of a varying electric current in a coil by the variations of magnetic flux from the tape. A disadvantage of this kind of repro duction lies in the fact that the out put signal is proportional to the rate of change of the flux in the tape rather than to the instantaneous values. The resulting frequency characteristic in creases from zero linearity until limited by the gap size. Since flux here is directly proportional to the input signal, the output from a conventional head is not a true reproduction of what was recorded. Equalizing networks must be incorporated in the reproducing circuits to restore the balance between low and high frequencies, so the repro duction will sound like the recorded signal. The solution of this problem is im portant in more than one respect. Many varieties of low-cost tape are now available and are finding increasing use in memory devices and the record ing of direct or telemetered data. A very elegant solution has been de scribed by A. M. Skellet, L. E. Leveridge, and J. Warren Gratian [Elec tronics, 26, No. 10, 168 (1953)]. In this development, standard magnetic tape is run over the neck of a special
Clay-Adams
miniature cathode ray tube causing an electron beam to deflect between two collecting plates alternately at the re corded audio rate, so that the current output of the tube is linearly propor tional to the magnetization on the tape. The new recording head gives an average output of the order of 200 mv. compared with 10 mv. for a conven tional head. The frequency response is very nearly flat, in sharp contrast to the conventional head. However, a drop at high frequencies occurs which is easily compensated by a simple filter section. The new method shows great promise for perpendicular re cording involving magnetization through the tape rather than longi tudinal recording. In certain appli cations where it is desirable to record very low frequencies, d.c. levels, or pulses without distortion, the new head is ideally suited, whereas the old type will not perform adequately with out considerable auxiliaries such as the dithering head or frequency modulation. Mercury
Jet
Switch
Many instrument problems require switching from one to another of sev eral circuits at high speed and at low noise levels. A new type of high speed, multipoint selector switch for electrical contact action termed a mercury jet switch has been described [Hoff, R., Instruments, 26, 1538 (1953)]. This article also describes a typical application of a series of these switches in a temperature mapping and monitor ing system, wherein 49 temperatures are repeatedly monitored every tenth of a second. The mercury jet switch consists of a Bakélite commutator having a circular arrangement of contact pins about a rotor. A fine j et of mercury is emitted from this rotor to scan each contact in sequence as the rotor revolves. Mercury-wetted contacts are used, so that switching takes place between liquid mercury surfaces. This identity of contact surfaces and the absence of rubbing mechanical friction combine virtually to eliminate switching transients. A jet switch of this type has been operated at rates up to 1800 points per second with a noise level of 20 microvolts across 200 ohms. While it is true that considerable advances have been made in conventional rotary commutator-type switches, it is probable that speeds of this magnitude have not been attained in this manner. ANALYTICAL
CHEMISTRY
