The tedium of his captivity was further relieved by his devotion to those scientific and mechanical pursuits which, all through life, yielded employment very solacing to himself, and very profitable to the world. While in the King's Bench Prison he was especially occupied in completing a plan for lighting the public streets by means of a lamp invented by him, in which the main principle was the introduction of a steady current of fresh air into the globes, whereby all the oil was fairly burnt, and a brilliant light was always maintained. In this way lamps much cheaper than those previously in use were found to have a far greater illuminating power. Early in October, 1814, the lamps in St. Ann's parish, Westminster, numbering eight hundred in all, were taken down and replaced by four hundred constructed on Lord Cochrane's plan; and even political opponents spoke in acknowledgment of the excellent result of the change. Had it not been for the introduction of gas, the superiority of these new lamps must soon have compelled their adoption all over London. It is curious that the discovery of the illuminating power of gas—undoubtedly due to his father—should have superseded one of Lord Cochrane's most promising inventions as soon as it had been brought to recognized perfection.
In such pursuits nine months of the unjust imprisonment were passed. "Lord Cochrane has hitherto borne all his hardships with great fortitude," wrote one of his most intimate friends on the 10th of November, "and, if there are any more in store for him, I hope he will continue to be cheerful and courageous." "His lordship always hopes for the best, and is never afraid of the worst," said the same authority on the 9th of December, "and therefore he is in good spirits."
This fearless disposition led, in March, 1815, to a bold step, which some of Lord Cochrane's best friends deprecated. Knowing that he was unjustly imprisoned, he conceived that, since his re-election as member for Westminster, the imprisonment was illegal as well as unjust, in that it was contrary to the privilege of Parliament. The law provides that "no Member of Parliament can be imprisoned either for non-payment of a fine to the King, or for any other cause than treason, felony, or refusing to give security for the peace." It may be questioned whether, in the presence of this law, his first imprisonment, even under the sentence of the Court of King's Bench, was legal. But having been imprisoned, and having been expelled from the House of Commons, it is clear that his subsequent re-election could not interfere with the fulfilment, of the sentence passed against him, especially as he had not been able to make good his title to membership by taking the prescribed oaths and claiming a seat in the House. He, however—acting as it would seem under the advice of William Cobbett and other unsafe counsellors—thought otherwise, and considered that he was only vindicating a high constitutional principle, against the exercise of despotic power by the Government, in making his escape from the King's Bench Prison. "I did not quit these walls," he said in a letter addressed to the electors of Westminster, on the 12th of April, "to escape from personal oppression, but, at the hazard of my life, to assert that right to liberty which, as a member of the community, I have never forfeited, and that right, which I received from you, to attack in its very den the corruption which threatens to annihilate the liberties of us all. I did not quit them to fly from the justice of my country, but to expose the wickedness, fraud, and hypocrisy of those who elude that justice by committing their enormities under the colour of its name. I did not quit them from the childish motive of impatience under suffering. I stayed long enough to evince that I could endure restraint as a pain, but not as a penalty. I stayed long enough to be certain that my persecutors were conscious of their injustice, and to feel that my submission to their unmerited inflictions was losing the dignity of resignation, and sinking into the ignominious endurance of an insult."