Pleased with hurting others, inhuman

The 8th amendment to the US constitution seems fairly explicit, until we look at the words in more detail:

Amendment VIII

Excessive bail shall not be required, nor excessive fines imposed, nor cruel and unusual punishments inflicted.

For example, what was “excessive” in the 1780s in monetary terms is minor now (a dollar then was worth far more than a dollar now), and thus what is excessive now has to seen in relative terms. What did the common people who voted for and against the amendments think the words meant?
To get some idea of an average view we can look at Johnson’s dictionary (1755, thirty or so years before the 8th’s ratification):

Excessive

Beyond the common proportion of quantity or bulk.

Cruel

Pleased with hurting others; inhuman; hard-hearted; without pity; without compassion; savage; barbarous; unrelenting.

Unusual

Not common; not frequent; rare.

Punishment

Any infliction imposed in vengeance of a crime.

In 1777 the US Congress knew what constituted cruel treatment of prisoners, as shown by General George Washington’s letter to British commander Lord Howe about the inhuman treatment of imprisoned sailors on ships in New York harbour (including overcrowding):

To RICHARD, LORD HOWE Head Quarters, January 13, 1777.
    My Lord: I am sorry that I am under the disagreeable necessity of troubling your Lordship with a Letter, almost wholly on the Subject of the cruel Treatment, which our Officers and Men in the naval Department, who are unhappy enough to fall into your hands, receive on board the Prison Ships in the Harbour of New York. Without descending to particulars, I shall ground my complaint upon the matter contained in the enclosed paper, which is an exact Copy of an Account of the usage of the Prisoners, delivered to Congress by a Captain Gamble, lately a Prisoner himself in New York.
…
    From the Opinion I have ever been taught to entertain of your Lordship's Humanity, I will not suppose, that you are privy to proceedings of so cruel and unjustifiable a nature; and I hope that, upon making the proper Inquiry, you will have the matter so regulated, that the unhappy Creatures, whose Lot is Captivity, may not in future have the Miseries of Cold, disease and Famine, added to their other Misfortunes. [My emphasis, see this account.]

The 8th amendment thus seems to be explicitly framed to take into account the worries of those in the Congress before and after independence: about over-crowding, miseries of cold, disease and famine of prisoners – banning such treatment precisely because it was cruel and thus not humane.
This amendment prohibits cruel treatment, but – as with many other parts of the US Constitution – it is a prohibition without any explicit sanctions. The recent US Supreme Court case (Brown v Plata et al) about over-crowding in California’s prisoners thus has two aspects:

1. Do the conditions of prisoners in California penitentiaries, constitute cruel or unusual punishment? And, if the conditions are cruel or unusual,
2. How can the state of California remedy the unconstitutional conditions of prisoners within its state system?

The US Supreme Court found prison conditions in California to constitute cruel and unusual punishment (1), and then the majority decided that to remedy that situation prisoners needed to be released (2). As the remedy to cruel and unusual punishment is not specified by the 8th amendment, then whatever remedy is mandated by the court, though legal, is extra-constitutional and thus open to rhetoric, such as that of Antonin Scalia in his dissent:

One would think that, before allowing the decree of a federal district court to release 46,000 convicted felons, this Court would bend every effort to read the law in such a way as to avoid that outrageous result. [My emphasis]

Scalia wants the other justices to bend the law to suit his extra-constitutional wishes. George Washington wanted the British to release prisoners to reduce overcrowding, by swapping prisoners held by the USA for some of those on the British prison ships.