--+----------+-----------------+----------------+---------------+
| 21 | .02846 | .002405 | 415.8 | .3581 |
| 22 | .02535 | .001907 | 524.4 | .4513 |
| 23 | .02257 | .001512 | 661.3 | .5693 |
| 24 | .02010 | .001199 | 833.9 | .7178 |
| 25 | .01790 | .0009513 | 1051. | .9051 |
| 26 | .01594 | .0007544 | 1326. | 1.141 |
| 27 | .01419 | .0005983 | 1671. | 1.440 |
| 28 | .01264 | .0004743 | 2108. | 1.815 |
| 29 | .01126 | .0003761 | 2659. | 2.287 |
| 30 | .01003 | .0002982 | 3353. | 2.883 |
| 31 | .008928 | .0002366 | 4227. | 3.638 |
| 32 | .007950 | .0001876 | 5330. | 4.588 |
| 33 | .007080 | .0001488 | 6721. | 5.786 |
| 34 | .006304 | .0001180 | 8475. | 7.297 |
| 35 | .005614 | .00009358 | 10686. | 9.201 |
| 36 | .005000 | .00007419 | 13478. | 11.60 |
| 37 | .004453 | .00005885 | 16994. | 14.63 |
| 38 | .003965 | .00004668 | 21424. | 18.45 |
| 39 | .003531 | .00003700 | 27026. | 23.26 |
| 40 | .003145 | .00002937 | 34053. | 29.32 |
+---------+----------+-----------------+----------------+---------------+

_Differentially-Wound Unit._ Another type of resistance coil is that
in which the winding is placed upon an insulating core of
heat-resisting material and wound so as to overcome inductive effects.
In order to accomplish this, the wire to be bound on the core is
doubled back on itself at its middle portion to form two strands, and
these are wound simultaneously on the core, thus forming two spirals
of equal number of turns. The current in traversing the entire coil
must flow through one spiral in one direction with relation to the
core, and in the opposite direction in the other spiral, thereby
nullifying the inductive effects of one spiral by those of the other.
This is called a _non-inductive winding_ and is in reality an example
of differential winding.

_Lamp Filament._ An excellent type of non-inductive resistance is the
or