Letter from William Herschel to an unnamed correspondent

Sir
I have the honour of your much esteemed letter and feel very forcibly that your approbation of philosophical pursuits is one of the greatest encouragements for perseverance. The subject of light has ever been one of my favourites, and polar observations have lately connected caloric with it. Some experiments which were not sufficiently established for want of clear weather, but which I hope soon to complete remain yet to be added to those I have already given. They are all of such a nature as to go to clear up our conceptions about caloric. There is a possibility that, although it be equally refrangible(?) with light, (the proof of which I mean hereafter to give more at length) it may not be the same(?) agent with respect to its matter. And if light can be fairly separated from caloric in the way I wish and shall try to do it, we should be able to decide the question.
I received Mr Delasande’s(?) almanac very safely, but was not desirous to take up any of your time in reading a letter of acknowledgement.
Dr Parry will be highly gratified by your obligingly agreeing to receive his communication, and I have written to him by this days post.
I remain ever with great respect
Sir
Your most obedient servant(?)
Wm Herschel

Slough
Near Windsor
March 20, 1800