. Strumenti e metodi utilizzati in radiometria. Boccole isolate nel telaio, h, h. Per testare la sensibilità i fili isolati a due linee sono saldati alle estremità della striscia bolometrica esposta, Fig. 16. Con il collegamento di questi fili ad alta resistenza, ad esempio 100,000 ohm,la deflessione ottenuta disbilanciando il ponte è ameasure della sensibilità del galvanometro. Per le osservazioni di routine pro-longed, può essere montato un contenitore per ridurre la sensibilità del galvanometro per TV> 2T> 5T> e Th, un interruttore di inversione e un interruttore per shuntare il thebolometer, come appena indicato

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. Instruments and methods used in radiometry . insulated bush-ings in the frame, h, h. Fortesting the sensitiveness twofine insulated wires are solderedto the ends of the exposed bo-lometer strip, Fig. 16. By con-necting these wires with a highresistance, say 100, 000 ohms, the deflection obtained by thusunbalancing the bridge is ameasure of the sensitiveness ofthe galvanometer. For pro-longed routine observations, ashunt box for reducing the sensitiveness of the galvanometer byh tV> 2T> 5T> and th, a reversing switch and a switch to shunt thebolometer, as just indicated, may be mounted in one box, whichgreatly facilitates the work. The largest wires, /, /, Fig. 16, of constantan are 1.4 mm diameter and have a resistance of 0.3ohms per meter. By moving the mercury contact 0.01 mm thechange in resistance is 0.000 03 ohm, or by joining the wire asshown by the dotted lines, Fig. 16, the change in resistance is0.000015 ohm. For the coarse adjustment, constantan wires/, /, having a diameter of 0.63 mm and a resistance of 1.4 ohms. cm Fig. 14.—Sliding con tact. •Ill Ihillei in of the Bureau of Standards. [ Vol. 4. No. 3. per meter were used. With this combination it was possible tobalance the bolometer so close (using the coarse adjustment) thaton permanently closing the galvanometer circuit the deflectionwould be only from 2 to 3 cm, which was then brought back tozero by means of the fine adjustment. By connecting the slidingcontact and balancing coils, as indicated, it is possible to balancethe bridge with but little adjustment on the slide wire, /, /. Anincrease in resistance on one side of the bridge corresponds to adecrease on the other side. This permits the use of less wire, and the whole can be confined in a smaller space than would havebeen possible in some of the previous instruments if an attempthad been made to place the bolometer and balancing coils andslide wire in one case. L S&A

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