hmmmm - i managed to miss the size, just looking at the photograph. But a bell like that might have some medical purpose yet - but then again, maybe not...
Cobalt glass and manufacturing method point at anytime 1780s thru 1890s - I guess it would be mid to late 19th ct. Around the 1870s blue glass was associated with health. If you feel under the weather, bathe in blue light and grow your vegetables in a blue greenhouse. It could be a blue dome to cover your vegetables while growing.
But more likely is a gardener's tool to isolate a sick plant - the clear variety was often seen in hyacinth growing to stop 'yellow rot' from spreading through the fields.
So whatever it will turn out to be, there is a story to tell....