. Sensitivity and magnetic shielding tests of a Thomson galvanometer for use in radiometry . was obtainable with these 20-ohm coils joined in parallel, itwas deemed desirable to determine whether (without making aprolonged investigation) an efficient coil could be found by trial,which had the properties of the central and outer sections of the20-ohm coil. As is well known and as was mentioned in a pre-vious paper,6 owing to the difficulties in winding fine wires andowing to the large amount of space occupied by the insulationwhen using fine wires, a more sensitive 4-ohm coil galvanometeris to
. Sensitivity and magnetic shielding tests of a Thomson galvanometer for use in radiometry . was obtainable with these 20-ohm coils joined in parallel, itwas deemed desirable to determine whether (without making aprolonged investigation) an efficient coil could be found by trial,which had the properties of the central and outer sections of the20-ohm coil. As is well known and as was mentioned in a pre-vious paper,6 owing to the difficulties in winding fine wires andowing to the large amount of space occupied by the insulationwhen using fine wires, a more sensitive 4-ohm coil galvanometeris to be expected to result from constructing the coils of heavywires (hence of low resistance, say ohms) which are joined inseries than is to be expectedto result from coils of the same sizewhich are wound with fine wire (hence of high resistance, say 10 4 Ayrton, Mather, and Sumpner, Phil. Mag., 30, p. 58; 1890. 5 Abbot, Astrophys. Jour., 18, p. 1, 1903; Ann. Astrophys. Obs., 1, p. 250, 1902. 6 This Bulletin, 11, pp. 1S0-1S1. (See Fig. 9-) 426 Bulletin of the Bureau of Standards [Vol. 13. , ohms) which are joined in series parallel. However, as will beshown presently, these two kinds of coils differed but little in theforce exerted, although the wires had been selected to give closelythe same sized coils. In previous tests no marked difference wasfound in galvanometers having 20-ohm coils wound in threeand in five sections of graded wire. The records of the perform-ance, of 12 galvanometers indicate (as mentioned in the paper justquoted) that the greatest advances in increasing the sensitivity of the galvanometer are to beexpected from improvementsin the suspended system. The mandrels used in wind-ing the coils were of two types,producing coils of the formshown in Fig. 1, which showsa compound coil wound inthree sections of graded Xo. 2 was tried todetermine whether a markedimprovement would result inthe magnetic field near thegalvanometer needles. Whenusing fi
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