Lizzie, My 2Xgreat grandfather, John Luffman did much the same thing in the reverse direction. He joined the Somerset Fencible Militia at Bath in February 1794, and followed with the unit to Alford Lincs. The purpose of the movement of the Militia was to resist a Napoleonic Invasion, the Authorities were concerned at the possibility of risings in favour of Napoleon and believed that Militia units from another part of the country were more likely to obey their officers and shoot the locals if ordered than troops from the vicinity. Hence the troop movements, in my ancestor's case to Alford Lincs. The detailed movements of these units is recorded in the Muster rolls held at Kew, and it is quite likely that your ancestor joined when the unit passed through his home town. A visit to Kew Archives would determine this. The records for the Somerset Militia, the monthly pay lists include the names of all the troops and not just the officers so if they have survived you will be able to follow his career from start to finish. By the way, at that time Boston was a centre notorious for revolutionary intrigue, and there were several incidents, so the authorities' concern had some foundation, but in view of the number of weddings between militiamen and local women (9 in Alford including my ancestor in 1798 alone) I do wonder if the would have obeyed orders if ordered to shoot?