. Carnegie Institution of Washington publication. 390 Special Reports No appreciable error is introduced through defective insulation. Shortly after the coils were wound the resistance between the adjacent coils of either group was not less than about 100,000 megohms. The resistance was much less some months later, when the spool had long been in a very damp atmosphere, but was still far too great to make any correction necessary. The original value can doubtless be restored and kept permanent by thorough drying and subsequent coating with paraffin. The total error in the constant is probably
. Carnegie Institution of Washington publication. 390 Special Reports No appreciable error is introduced through defective insulation. Shortly after the coils were wound the resistance between the adjacent coils of either group was not less than about 100,000 megohms. The resistance was much less some months later, when the spool had long been in a very damp atmosphere, but was still far too great to make any correction necessary. The original value can doubtless be restored and kept permanent by thorough drying and subsequent coating with paraffin. The total error in the constant is probably less than 1 part in 30,000. The mean diameter of coils 1 and 4, which will be treated as one Helmholtz pair, is, :iccording to Table I, d = mm. at 23° C, while the mean axial distance between corresponding turns for the same pair at the same temperature is, according to Table II, a-= mm. The number of turns N being assumed as exactly 20, equation (5) gives for the constant G,, of this pair, at 23° C, (?14 = gauss electromagnetic unit current In the same way we obtain for the constant G2i of coils 2 and 3 G!23 = gauss electromagnetic unit current and for the coils connected in series the constant (9) (10) G = Gh+G^ gauss electromagnetic unit current According to these equations, Gu is greater than Gu by about 1 part in 24,000. As an experimental check, the instrument was set up as a tangent galvan- ometer, with the axis of the coils in the magnetic prime vertical, and double deflections were observed (1) when a current of ampere was sent through the coils 1 and 4 in series in the same direction, and (2) when a current of amperes was sent through the system with coils 1-4 opposed to coils 2-3. Deflections of 245 divisions in the first case and divisions in the second case showed that Gu exceeded G2i by parts in 24,500. The discrepancy between the calculated ^1 ____). r_ ^ and experimental differences, only 1 part in 60,
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