This mild domestic gambling game appeared towards the end of the 18th century and disappeared about a hundred years later. Jane Austen mentions it several times, notably in this passage from Mansfield Park:
What shall I do, Sir Thomas? [asks his wife]: Whist and speculation; which will amuse me most?'
Sir Thomas, after a moment's thought, recommended speculation. He was a whist player himself, and perhaps might feel that it would not much amuse him to have her for a partner.
Dickens also mentions it in Nicholas Nickleby (1839), while Charles Pardon, in The Card Player (1868), maintains that "As a merry game for Christmas parties speculation is without a rival". It figures in Cassell's Indoor Amusements, Card Games and Fireside Fun (1881), but must have been on its way out by then as no mention is made of it in the otherwise comprehensive Foster's Complete Hoyle of 1897.
The following description is from the 1847 edition of Hoyle's Games. By an extraordinary coincidence, the same wording is found in Bohn's Hand-Book of Games (1850).
This is a noisy round game, that several may play, using a complete pack of cards, bearing the same import as at whist, with fish or counters, on which such a value is fixed as the company may agree upon. The highest trump, in each deal, wins the pool; and whenever it happens that no trump is dealt, the company pool again, and the event is decided by the succeeding round. After determining the deal, &c., he who is to deal pools six fish, and every other player four; next three cards are given to each player by one at a time, and another turned up for trump, which belongs to the dealer, who has the privilege of selling it to the highest bidder, unless it be an ace, which gives him the pool at once. The cards are not to be looked at except in this manner: - the eldest hand shows the uppermost of his three cards, which, if a superior trump to the dealer's, the company may speculate on, by bidding for it as before. When this is settled, he who sits next to the purchaser is considered as eldest hand, and shows the uppermost of his cards; but if the first card shown should not prove a superior trump, then the next in order to the first player shows the uppermost of his cards, and so the showing goes on, the company speculating as they please, till all the cards are discovered, when the possessor of the highest trump wins the pool.
N.B. The holder of the trump, whether by purchase or otherwise, is exempted from showing his cards in rotation, keeping them concealed till all the rest have been turned up.
To play this game well, little more is requisite than recollecting what superior cards of the trump suit appeared in the preceding deals, and calculating thereby the probability of the trump offered for sale proving the highest in the deal then undetermined.