by an Act of the 43d of George III. Cap. 96. [1803, Defence of the Realm etc.] enabling His Majesty more effectually to provide for the defence and security of the Realm during the present War, all persons, from the age of 17 to 55, are ordered to be called out, for the purpose of being trained to the exercise, and to learn the use of Arms, in the manner particularly directed by the said Act of Parliament; and that by the 53d Section of said Act it is provided, that where a sufficient number of Persons, between the age of 17 and 55, shall engage to serve as VOLUNTEERS, .....and to be trained, exercised, drawn out, and embodied, under the conditions therein mentioned; and to March to any part of Great Britain for the defence thereof, on any Invasion, or on the appearance of an Enemy in any force on the Coast; or to suppress any Rebellion or Insurrection arising, or existing, during such Invasion, whenever we shall be called out by the LORD LIEUTENANT of the County of AIR, in which County we are formed: His Majesty having been pleased, for our encouragement, to order that each VOLUNTEER shall receive Twenty Shillings in three years, for clothing, and One Shilling per day for 20 days in the year, besides the sums specified in the Act. And we Agree to furnish ourselves with Arms and Accoutrements, or the same shall be furnished to us by Government, as is particularly specified and annexed to our respective names, in the Columns in which we subscribe.
Take a look at this youtube clip with some early photos of Dalmellington. They post date when Robert and Mary lived there but many will give you an idea of how the town might have been at the time.