Googling the words "Ernst Beck CO2 measurement" brings quite a few hits referring to the work of the late Ernst Beck from Germany who investigated hundreds of old CO2 measurements from early 1800s onwards. ,
Most of the hits come from "climate skeptic" sites since his conclusion was that climate science has on purpose omitted the results of these studies so that the theory of man made climate change would hold.
However, his results have considerable issues that have not yet been answered, like
1) The variation of CO2 levels stopped as soon as modern measurements started in the end of 1950s. After that they have consistently increased and now at 400 ppm level. If the variations reported by Beck were real this surely would have continued after late 1950s as well.
2) The huge CO2 concentration variations reported up to the end of 1950s would have require enormous flows of CO2 release and subsequent capture within short period of time. However, there has been no evidence of this having taken place.
But, if we accept that the samples analysed in these earlier experiments reflect more of a local inland background CO2 , than global background, everything starts to make sense and fits together. Environment itself and height from which samples are drawn has big influence to the results and it is quite understandable that these old results show such impacts and that these show big variations.
Personally I find this latter explanation far more plausible than the story line of Beck's site amplified by WUWT, Joanna Nova, Tim Ball, Heartland Institute and others essentially involving a global conspiracy of climate scientists to distort data spanning several decades and joined by IPCC report after report. , , .