A spectroscopic instrument comprising a compartment (2) for housing instrument components (3) and desiccant (4) to protect the instrument components, and a deformable container (5) having at least one wall portion which is movable within the compartment (2) so as to vary the volume of the compartment (2) that is occupied by the deformable container as the container is deformed. The interior of the deformable container (5) is in fluid communication with the surroundings of the instrument, such that a difference in pressure between the compartment and the surroundings tends to cause the deformable container to deform, moving the wall portion.