R W Wood: Physical Optics

Posted: November 26, 2014 by tchannon in books, History, radiative theory


Solar spectrum due to Langley published in “Physical Optics, Robert W Wood, Professor of Experimental Physics in the John Hopkins University, year 1905, page 477.

R W Wood has been mentioned on the Talkshop so when a-private-place references the early edition is out of copyright I thought it would be useful to point. (no cite unless the person tells me to)

I am aware of Langley’s later work with Angstrom but this is very early.

The frenetic work in society up until 1910 never ceases to amaze me. Excitement over telegraphs and telephones, electric lighting, generating, motors and so on. At least as interesting is history not as popularly supposed on who really did what. Physics was no different.

The Angstrom (youngster)/ Langley (not so young) matter is illustrated by the former using electrical instrumentation, Langley calorometers. For that matter the use of photography for remote sensing, recording instrument traces.

This came essentially with the S curve of development, the steep climb after invention, figure out and development to commercial commoditisation of electricity and all that goes with it.


Page 456

The book is available in various forms, images or as OCR.

Microsoft sponsered the scan, archive.org distribute and therefore anyone feeling flush, drop the latter a donation.

The PDF is images, best bet for legibility, 41MB, epub 1.8MB but OCR is iffy.

Some usage online via javascript might be enough for some.


I might be able to extract sections from PDF and make those available, from past experience in practice a bit of a tricky process.

Post by Tim

  1. steverichards1984 says:

    This book, what a find!

    From page 456, “found that a layer of gas (CO2) 7cm thick emitted and absorbed as strongly as a layer of 33cm thick. This indicated that radiation from a 7cm layer could be regarded as the radiation from an infinite thickness.”

    That was from an experiment conducted in 1894 by Paschen.

    The book goes on to describe ‘real’ physical experiments, how the apparatus was made and worked.

    Those were the days of finding fundamental processes…..

  2. David Blake says:


    Nice spot!

    I’m a bit math challenged but would that be equivalent to saying that for 400ppm CO2 all the radiation at that wavelength would be absorbed by 17,500cm? 7/(400/1,000,000) = 17.5 metres

    .. and any increases in co2 would mean an even shorter absorbtion distance?

  3. David Blake says:

    Doh! 175 metres! (Told you I was math challenged!)

  4. tchannon says:

    Such a spectrum envelope should not be taken as the radiative capacity of a continuous spectrum, will be much less.

  5. Brett Keane says:

    Thanks Tim, got a pdf of it. This is the real McCoy! Brett