This busy envelope cover demonstrates how much more complex the international postal system was in the last century. Sent from Dublin to a recipient in Degersheim, Switzerland, the letter travelled via London, Hamburg and Berlin using both Imperial Airways and Deutscher Aero Lloyd. Expected to fetch £200-£300, the envelope is just one of almost 500 lots being offered next weekend by Dublin auctioneers Whyte's in a sale of stamps and postal history items.

Three letters of particular interest were sent to Dublin on separate dates from Paris while the latter city was under siege by the Prussian army in 1870; the method used to transport them was hot-air balloon, and they carry estimates between £300 and £1,000.

Similarly, a series of 14 envelopes from Ireland to South America carried on the Graf Zeppelin airship are expected to fetch from £250 and £500 apiece. Then there are two letters salvaged from aeroplane disasters; that taken from a KLM flight which crashed seconds after it had taken off from Shannon airport in 1954 has a pre-sale estimate of £100-£120, while one from a crash at Lahinch 20 years before is expected to make £300-£400. The sale, in the company's Marlborough Street premises on Saturday, April 28th, begins at 1.30 p.m.