It looks very smart for an Admiral Fitzroy (he of 't shipping area). Is it new-ish or restored?
The problem isn't a big one, as John says. It's simply a matter of re-establishing the (Torricellian) vacuum properly, at the top of the sealed end of the tube. The people in Leominster can do this, easily.
Watch out for the escaped mercury though. It can get out of the case, just like water could. The best thing would be to place the whole thing in a plastic bag (bin liner?). There will be a significant vapour pressure behind the glass - keeping it as cool as possible will help, too, until you get it to a restorer to fix it.
Aside: my own, unrestored barometer is the banjo type (C19th). The only real difference with the Fitzroy ones is that there is a float and a mechanical linkage to the needle. It's still got a mercury column arranged in a similar way. Happily, so far, nobody has lain it down or inverted it, but when I get a round tuit, it'll be making the trip to Leominster too, well two trips, actually, I hope. The first one will be to remove the mercury, allowing me to restore the case, then I'll get it set up again once it's done.
Regards,
E.
