The London, Edinburgh and Dublin philosophical magazine and journal of science . ng from thefact that Lenard and others, using very high frequencies,.have found a negative effect in no field ; with the lowfrequencies used in my experiments the negative effect canjust be detected, but could not be satisfactorily measured. Temperature were next undertaken to find the effect oftemperature variations on the bismuth In all the previous experiments a Hartmann &, Braunbismuth spiral, designed for field-testing, had been used, butthis became useless when experiments were
The London, Edinburgh and Dublin philosophical magazine and journal of science . ng from thefact that Lenard and others, using very high frequencies,.have found a negative effect in no field ; with the lowfrequencies used in my experiments the negative effect canjust be detected, but could not be satisfactorily measured. Temperature were next undertaken to find the effect oftemperature variations on the bismuth In all the previous experiments a Hartmann &, Braunbismuth spiral, designed for field-testing, had been used, butthis became useless when experiments were made at otherthan atmospheric temperatures, so it was replaced by a wire*3 mm. in diameter and about 10 cm. long, bent into the form Fis. 5. of a flat grid and soldered to two thick copper wires (fig. 5).These grids were very easily broken, and a number were usedduring the experiments ; the bismuth wire was supplied byMessrs. Hartmann & Braun. For temperatures above atmospheric a grid was placed ina glass vessel (fig. 6) consisting of an inner vessel having a Fiar. fiat tube joined on at the bottom, into which the bismuthwire projected, surrounded by a similar slightly larger vessel. 558 Mr. G. C. Simpson on the Electrical In the space between the two, water from a thermostatcirculated, so keeping the bismuth (placed in oil) at therequired temperature. For temperatures below atmospheric a similar vessel wasused, except that the space between the two walls was evacuated,and different freezing-mixtures placed in the inner vessel. Low temperatures were obtained as follows :—Liquid airgave a constant temperature of —185°, a mixture of solidC02 and acetone gave —70°, while —95° was obtained bybubbling air through this mixture; solid C02 in alcoholproduced —40°. The bismuth wire having a very low resistance (about 2 ohmsat 17°) and the field being comparatively weak, owing tothe large separation of the pole-pieces necessitated by theglass vessel, the whole effect t
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectscience, bookyear1840
