The Photographic and fine art journal . the natural action of the earths magne-tism and the free magnetism of the bar, and that a variation ofeither of these elements will induce a corresponding change ofposition of the magnet. In order, therefore, that the magneticcurve may truly represent the changes in the earths force, it isnecessary that the variations of force in the bar itself should bemechanically counteracted by the same agency that producesthem, namely, change of temperature. Fig. 3, is a representation of the self-registering thermome-mometer and psychrometer. This is essentially a
The Photographic and fine art journal . the natural action of the earths magne-tism and the free magnetism of the bar, and that a variation ofeither of these elements will induce a corresponding change ofposition of the magnet. In order, therefore, that the magneticcurve may truly represent the changes in the earths force, it isnecessary that the variations of force in the bar itself should bemechanically counteracted by the same agency that producesthem, namely, change of temperature. Fig. 3, is a representation of the self-registering thermome-mometer and psychrometer. This is essentially a wet and drybulb self-registering thermometer. The bulbs of the thermome-ters are placed underneath the table, through which the stemspass vertically, and are placed between the opposite sides of thecylinders and two lights. A narrow vertical line of light,brought to a focus by a cylindrical lens, falls on the stem of thethermometei-, and passing through the empty portion of thebore, affects the prepared paper. The boundary between the. Fig. 3 —Brookes Self-Registering Thermometer and Psychrometer. dark and undarkened portions indicates the position of themercury in the stem of the thermometer. Fine wires are placedacross the slit in the frame through which the light falls on thestem; and coarser wires at every 10th degree as well as at cer-tain other fixed points of the scale, namely, 32, 54°, 16°, and THE PHOTOGRAPHIC AND FINE ART JOURNAL. August, 98*. The shadows of these wires protect the portions of thephotographic paper on which they fall from the action of light, andthe darkened surface of the paper is consequently traversed by aseries of parallel pale lines; and the relative position of thebroad and narrow lines readily explain the temperature indicat-ed by the register. In this illustration figures are used insteadof letters:—1, 2, are camphine lamps, now superseded by gas,whereby tlie time and labor of trimming, and a greater uniform-ity of light has been obtaine
Size: 1318px × 1897px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1850, bookidphotographic, bookyear1854
