I'm helping with a War of 1812 thing and a curator came to me with a very specific question. The British raided the port of Alexandria (then part of DC) after they burned the American capital of Washington. Their ships docked either at the wharf or just offshore during this event, depending on their draft. Just outside of town, at an elevated piece of land called Shuter's Hill, a band of militia gathered. The uniforms were likely blue fringed with red, so the colors would probably have popped on a fairly deforested hill in late summer. There were no buildings nor trees tall enough to have blocked the view. Here's the question:
Could a British officer at approximately 1.5 miles distant and using a period spyglass have seen this militia?
Some calculations. A 5.75-foot militiaman at 8000 feet would have a visual angle of 0.041 degrees or 0.000716 radians.
With the naked eye, that militiaman would have the same perceived size as a 0.22 mm tall object (about the width of a human hair) viewed at a distance of one foot. So, that's not very feasible.
Now we turn to the spyglass. I am venturing outside my area of specialty here, so there are some unanswered questions. I'm assuming that a British officer would be responsible for furnishing his own spyglass, and that this hypothetical British officer would have a fairly average glass. At the time, a spyglass had an effective magnification of 4x or 5x - meaning the militiaman would be roughly a millimeter in size through the spyglass.
I took the liberty of creating this. You're missing a lot here - I didn't paste the militiaman against the sky or a green background, and there would be flashes of light from swords and muskets, and the sound of a large group of men on the move (I don't know how many men Hungerford had on Shuter's Hill, or whether this hypothetical British officer is looking into the sun). So while the British probably wouldn't be able to determine whether they were facing regulars or militia without sending a scout forward, they wouldn't have any problem seeing a large group of men gathered on the high ground (through glasses, at least) and determining whether they were hostile.
Also out of my area of expertise, but there is another important factor to consider. Before I get into it I would like to highlight that this is not what I do; anyone with corrections please speak up!
Weather is the factor I would like to bring up.
I seem to remember that one of our traditional late summer thunderstorms struck during the attack on Washington, eventually even producing a tornado that damaged many of the British ships on the river.
The Occupation of Washington was preceded with 100 degree heat. In late summer in DC this means humidity and heat haze. This would have been the 24th. The day following there was a massive thunderstorm and tornado system that drenched the city with rain and put out the fires.
Obviously this was several days before the raid on Alexandria, and I cannot find (in my current casual search) notes on the weather in the following days. It would not be out of the question, however, for either rain or heat haze to have been present in late August in the immediate DC area.
I will keep trying to find some weather records.
EDIT: Can't find anything on temperature or precipitation, just notes on wind direction. The wind that carried the British squadron up the Potomac to Alexandria continued to blow for several days, into very early September, preventing the ships from going down the river from Alexandria. Not much help, sorry.
