und coils, the
number of turns per linear inch and per square inch of B.&S. gauge
wires from No. 20 to No. 40 have been tabulated, and these,
supplemented by a tabulation of the number of ohms per cubic inch of
winding space for wires of three different kinds of insulation, are
given in Table IV.

Bearing in mind that the calculations of Table IV are all based upon
the "diameter over insulation," which it states at the outset for each
of four different kinds of covering, it is evident what is meant by
"turns per linear inch." The columns referring to "turns per square
inch" mean the number of turns, the ends of which would be exposed in
one square inch if the wound coil were cut in a plane passing through
the axis of the core. Knowing the distance between the head, and the
depth to which the coil is to be wound, it is easy to select a size of
wire which will give the required number of turns in the provided
space. It is to be noted that the depth of winding space is one-half
of the difference between the core diameter and the complete diameter
of the wound coil. The resistance of the entire volume of wound wire
may be determined in advance by knowing the total cubic contents of
the winding space and multiplying this by the ohms per cubic inch of
the selected wire; that is, one must multiply in inches the distance
between the heads of the spool by the difference between the squares
of the diameters of the core and the winding space, and this in turn
by .7854. This result, times the ohms per cubic inch, as given in the
table, gives the resistance of the winding.

There is a considerable variation in the method of applying silk
insulation to the finer wires, and it is in the finer sizes that the
errors, if any, pile up most rapidly. Yet the table throughout is
based on data taken from many samples of actual coil winding by the
present process of winding small coils. It should be said further that
the table does not take into account the placing of any layers of
paper between the successive layers of the wires. This table has been
compared with many examples and has been used in calculating windings
in advance, and is found to be as close an approximation as is
afforded by any of the formulas on the subject, and with the further
advantage that it is not so cumbersome to apply.

_Winding Calculations._ In experimental work, involving the winding of
coils, it is frequently necessary to try one winding to determine its
eff