I found about a trivial reference to it while reading Les Miserables, and I read the Wikipedia page. I was looking for more insight on why was it introduced. Grateful if anyone enlighten me. Thank you.
I don't know about France, but in England and Wales: basically, in the late seventeenth century, William III needed a lot of money. Coins back then were made of actual gold and silver, and people would 'clip' them - shave a little bit of gold or silver off each coin that passed through their hands, till they had enough to make a new fake one. This could easily go unnoticed, because those coins didn't have distinct edges and wore down naturally as they passed from hand to hand, so it wasn't weird to see one that wasn't perfectly round. This happened on such a scale that it undermined the country's entire currency. We're not just talking the occasional person shaving off a snippet here and there: people had organised coin-clipping enterprises in place. Here's Ann Petty, who in 1674 was convicted of having a network of apprentices and servants who would bring her their masters' coins; she would clip them, pay the servants a percentage, and give the clipped coins back to them to replace.
Various monarchs tried to put a stop to this. Punishments for clipping could go right up to execution - Ann Petty was 'brought in guilty of high Treason, and sentenced to be Drawn on an Hurdle or Sled to Smithfield (the usual place for such Executions) and there to be burned to Death'. Charles II demonetised some of the old coins and introduced new milled ones, with edges that would make clipping obvious. But there were still plenty of the old ones out there, getting clipped, and plenty of people willing to take the risk of getting caught. People hoarded the full-weight coins and passed on the clipped ones. Foreign merchants would only accept coins that weighed the proper amount, meaning that full-value coins gradually left the country. By the end of the seventeenth century, the vast majority of the coins circulating in Britain had been clipped.
Finally William III had had it with this. He decided on the Great Recoinage of 1696. He announced that he was recalling all the old coins, which would be redeemed at face value no matter what state they were in, and he was going to reissue the nation's entire coinage in milled form. (This went exactly the way you'd expect: people clipped the bejaysus out of their coins before handing them in, since they were going to get face value either way, thus making the problem even worse.)
Since he was reissuing a lot more gold and silver than he was taking in, William needed money to make up the difference. He and his government decided on a tax.
The idea of income tax was very controversial at this stage - the general feeling was that it was none of the government's damn business how much money you made. Britain had been trying out a Hearth Tax, where the occupier of a house paid a certain amount per fireplace twice a year. The logic was that richer people had bigger houses, therefore more fireplaces, therefore they would pay more. People weren't crazy about this, either, since it meant that the collectors got to come into your house and inspect it, and also because - even when exemptions were brought in - it was hard on poor people. (Historians love the records of hearth taxes - they act as a kind of abbreviated proto-census, giving information about population and wealth distribution in the seventeenth century. The Hearth Tax Project has digitised a load of them, and you can see them here if you're interested.)
So William's government decided on a Window Tax. This operated roughly the same way as the Hearth Tax, charging rich people more because they had more windows, but it had the advantage that it didn't require collectors to enter people's homes - they could just count from outside.
It sort of worked, only not really. People promptly started bricking up their windows, or just boarding them up and then taking off the boards after the collectors had been around. New houses were built with fewer windows, vents and lights. This led to one of the most strenuous arguments against the Window Tax: it reduced the amount of light and air people got, so it contributed to the spread of disease. In 1841, the architect Henry Roberts argued that in tenements, in particular, 'The policy of continuing a tax which so greatly conduces to augment the evils of an over-crowded dwelling, and at the same time presents a serious barrier to their improvement, by diminishing the fair return from such investments, can scarcely be matter for question.' (From his The Dwellings of the Labouring Classes, Their Arrangement and Construction.) There was also widespread corruption and general sloppiness around its enforcement.
The Window Tax was only supposed to last for seven years, but of course - like most 'once-off' taxes - it lasted a whole lot longer. Scotland and Ireland got brought in as well, and there were plenty of modifications and exemptions introduced along the way, but it only fully went out in 1851.
Here's the beginning of the Act for granting to His Majesty severall Rates or Duties upon Houses for making good the Deficiency of the clipped Money:
Wee Your Majesties most dutifull and loyal Subjects the Commons in Parliament assembled being deeply sensible of the great Mischiefs occasioned and brought upon Your Majesties Subjects by the clipping of the current Coyne of this Kingdome and that itt is necessary in order to prevent the like evills for the future that such clipped Money should bee recoyned And in regard such of Your Majesties good Subjects in whose Hands such clipped Money shall happen to bee must sustaine great Losse and Damage by reason of the Deficiency thereof upon the recoineing unlesse some Recompence be provided to make good such defect to the severall Owners and Proprietors thereof have therefore chearfully and unanimously given and granted to Your Majesty as a Supply and Ayd for and towards the makeing good the Deficiency of such clipt Money the Rates Duties Impositions and Summes of Money herein after menc[i]oned And wee most humbly beseech Your Majesty that it may be enacted And be itt enacted by the Kings most Excellent Majesty by and with the Advice and Consent of the Lords Spirituall and [Temporall & (fn. 1) ] Commons in this present Parliament assembled and by the Authority of the same That from and after the Five and twentieth Day of March in the Yeare of our Lord One thousand six hundred ninety six for and dureing the Terme of Seaven Yeares to commence and bee accounted from the said Five and twentieth Day of March and noe longer there shall be charged raised levyed and paid unto His Majesty His Heires and Successors For and upon every Dwelling House inhabited that now are or hereafter shall bee erected within the Kingdome of England Dominion of Wales and Towne of Berwick upon Tweed (other then and except Cottages) the annuall or yearely Summes of Money herein after mentioned (that is to say) Every such Dwelling [House (fn. 2) ] inhabited now erected or which hereafter shall bee erected within the Kingdome of England Dominion of Wales or Towne of Berwick upon Tweed the yearely Summe of Two Shillings And for every such Dwelling House inhabited having Ten Windows or more and under the Number of Twenty the Summe of Foure Shilling yearely over and above the said yearely Summe of Two Shillings And for every such Dwelling House inhabited having Twenty Windows or more the yearely Summe of Eight Shillings over and above the said yearely Summe of Two Shillings Which said Summes of Money shall bee paid yearely and every Yeare dureing the said Terme of Seven Yeares upon the Nine and twentieth day of September and the Five and twentieth day of March by even and equall Porc[i]ons the First Payment thereof to bee made upon the Nine and twentieth day of September which shall be in the Yeare of our Lord One thousand six hundred ninety six.
Paraphrased: We, the Parliament, know that coin-clipping has made a total mess of things. And we know that, when we do this recoining, people are going to lose a load of money unless we redeem their coins at face value. So we need to make up the shortfall. We propose that, for seven years from 25 March 1696, everyone in England and Wales should pay 2 shillings per house, plus 4 shillings for each house with 10 to nineteen windows, and 8 shillings for each house with 20 windows or more. Cottages are exempt. Everyone else should pay half on 29 September each year and half on 25 March, starting this 29 September.