Hollowing out wood log for table
So you are (if I get your idea correctly) looking at two large-diameter log sections, large enough that two of them would serve as all the legs needed for your table? Could be a nice look.

If you get lucky, you might find a hollow beech. Pine, less likely in usable form - if it's hollow it's usually also rotten outside that.

Assuming you don't get lucky: Your logs/cylinders have two ends, really - coat them both with something. But the biggest factor is to QUICKLY (or at least before bringing them inside where they will start to dry faster) hollow them out all the way through (not just at one end) so that they can shrink without excessive cracking. A large Forstner drill bit is probably the best method for doing this unless you have access to a large wood lathe, (but if you did, you probably wouldn't be asking this question or contemplating a chainsaw/chisel attempt at it.)

Lay out a circle on the end of the log, and drill overlapping holes to remove the bulk of the wood. Using a large-diameter bit (3 inches or so) will allow you to drill down to where the body of the drill is inside the cavity while still being straight. You will have to drill in stages, and probably from both sides. i.e. take a 18" diameter log, lay out a 14" diameter circle, and drill overlapping 3 inch holes all around the inside of the 14" circle, 3 inches deep; having made 3 inches of depth to work in (so that there is room to get the drill down that far), resume drilling another 3 inches deep, all over,  repeat once more, then flip and start from the far side and you can hollow an 18 inch long log.  

You can also use any of the (often overly complex) methods that folks dream up for "primitive drums" if you like - I'm simply promoting the quickest way I know, not making use of a large lathe...

If a more finished look worked for you, you could also buy some sonotube (very heavy cardboard concrete form tube) and apply wood veneer to the outside of it.