sporregar
In my house those were the main fuses. Pull those and the house goes black. There should be a glass window in the fuses that you can see if it's blown or not. You may just have too many things running at once on the same circuit or too much for the house's voltage. You may need an upgrade in service. Probably should have the place re-wired for circuit breakers.

jsa1962jsa
The black boxes most likely are knife fuse holders that hold cartridge type fuses that act as the main breakers in a modern fuse box. Pull them out and the whole house will go black. I doubt if they have any bearing on your brown out. More likely, that is caused by your modern appliance and fixture load exceeding the wiring capacity in the old house. Old houses had 15 amp fuses and few circuits, newer houses have 20 amp breakers and many more circuits so you have fewer things plugged into each circuit. Try turning off half of your appliances and lights and see if you still have the brown out problem. If it goes away, You have a capacity limitation in your house that you just have to work with, short or rewiring much of the house, that is.

gizmoe
Those are 220 volt fuse holders, one is probably the main fuses for the panel the other is for some other 220 volt appliance. Maybe a cookstove. Those will pull out and will hold 2 cartridge type filters. Unlikely that that is your problem, the fuses typicaly work or they dont. I would guess you have a problem with a connection maybe in the fuse panel. The ground circuit or nuetral is usually the culpret.

John himself
One of them holds the main fuses for the service. The other is typically fuses for the kitchen range. I am not sure what you mean by "failing" or "brown-out" so I can't guess what the problem might be. Try to be a little more precise as to what is happening. An electrician would use a meter to measure the voltage in various places in your home as well as at the service itself. Call one or get a meter. Be careful of taking electrical advise from well meaning but untrained people on yahoo.