In the second half of the nineteenth century, telegraph networks gradually extended across the surface of the globe. This development contributed to both concrete and symbolic processes of appropriation of the terrestrial environment by science and technology. Telegraphs were used to transmit and pool weather observation data. At the Paris Observatory, under the Second Empire, a group of scientists used a new forecasting method to manage observations centralized by telegraphic transmission of data. This « synoptic » method combined daily weather charts showing depressions with an appraisal of these maps, providing a series of forecasts without recourse to analytical methods. These forecasting techniques were quickly adopted worldwide, ultimately introducing a new « natural » object, the depression, into our intellectual and media landscape. The depression was the product of an industrial and mediatised society, caught up in the accelerated process of globalisation during the last thirty years of the nineteenth century. By studying the birth of techno-scientific weather forecasting, I offeran archeology of the contemporary atmosphere, which was shaped in powerful ways at this moment of profound transformation of scientific approaches to the terrestrial environment.