# Re: Aluminum magnet wire? and Circular # 74

```In a message dated 9/18/99 8:33:13 AM Central Daylight Time, tesla-at-pupman-dot-com
writes:

<< (It's not entirely right, but in general, doubling the diameter of the wire
only halves the resistance, not 1/4, as you might expect from 4 times the
area). >>

Huh?

>From the wire tables and using a #10 wire for an example:
The #10 diam is 101.9 mils and halves at a #16 to 50.82 mils.
Ohms / 1 k ft goes from 1.018 to 4.094...very close to 4 : 1.

The #10 diam doubles at a #4 to 204.3 mils.
Ohms / 1 k ft goes from 1.018 to 0.2533...again 4 : l

And now for something completely different:
I first read about circular No. 74 from postings on the Tesla list.
I don't know how rare this may be in the libraries around the planet, but
after learning of the existence of the National Bureau of Standards, Circular
No. 74, 1918, I found
a nearly complete collection of all the NBS circulars in the Indiana
University library.
There's more in Indiana than just basketball and popcorn. Circular No. 74,
Radio Instruments and Measurements, is a must for anyone who wants a great
text on radio theory from when the technology was young. The writing on
antennas and electromagnetism is clearly intended to instruct as wide an
audience as possible on the new technology. Probably of greatest interest to
coilers is the excellent derivation of the Medhurst and Wheeler equations.
Included in the text are tables and graphs giving the values for the
empirically derived constants over a wide range of coil dimensions. You don't
have to work thru the math. Here must be the source of much described in
Terman.

The entire text is around 340 pages including the index. I had to copy (at
Kinko's) two pages of text per 11 x 17 sheet so I have around 170 pages. I
made two copies. So what I am thinking is that while I do not have the time
to make (sell?) copies for all who might want a copy, if there is anyone out
there who would like to put this on their web page we might be able to figure