It is by the rarity with which the talent of seizing upon remote analogies is associated with a spirit of patient and subtile investigation of details, and a quick perception of their value, that the fact so truly stated by Mr. Babbage is to be explained; _viz._ that long intervals frequently elapse between the discovery of new principles in science and their practical application: thus he observes, that "the principle of the hydrostatic paradox was known as a speculative truth in the time of Stevinus, as far back as the year 1600,--and its application to raising heavy weights has long been stated in elementary treatises on natural philosophy, as well as constantly exhibited in lectures; yet it may fairly be regarded as a mere abstract principle, until the late Mr. Bramah, by substituting a pump, instead of the smaller column, converted it into a most valuable and powerful engine. The principle of the convertibility of the centres of oscillation and suspension in the pendulum, discovered by Huygens more than a century and a half ago, remained, until within these few years, a sterile though most elegant proposition; when, after being hinted at by Prony, and distinctly pointed out by Bonenberger, it was employed by Captain Kater as the foundation of a most convenient method of determining the length of the pendulum. The interval which separated the discovery of Dr. Black, of latent heat, from the beautiful and successful application of it to the steam-engine, was comparatively short; but it required the efforts of two minds; and both were of the highest order."[122] [122] "Reflections on the Decline of Science in England," page 15. The discoveries of Davy present themselves in striking contrast with such instances. The same powerful genius that developed the laws of electro-chemical decomposition, was the first to apply them for the purpose of obviating metallic corrosion; and the nature of _fire-damp_, and the fact of its combustion being arrested in its passage through capillary tubes, were alike the discoveries of him who first applied them for the construction of a safety-lamp.[123]