[2] This is true except when the tube is so small that capillary attraction exerts considerable influence. [3] I was once consulted in regard to a smoking stove. It was an open Franklin stove, the pipe of which went through a fire-board into a monstrous chimney. I recommended that a pipe with a knee should extend from the pipe of the stove a little way up the chimney. The expedient was successful, because but a small body of air, that in the pipe, needed to be heated to establish an upward current. [4] As in the case of many other inventions, so here the same idea was originated and put to practical use by more minds than one. George Stephenson, who from being a common engine-wright in a colliery rose step by step till he invented the locomotive, constructed a lamp which illustrated in another way the same principle as the lamp of Davy does--in other words, he invented another safety-lamp. But this does not in the least detract from the glory which the invention has given to the name of Davy, for each acted independently of the other. In Davy's case, it is to be remarked, there was a long course of scientific reasoning and investigation which led him at length to the invention, the record of which is exceedingly interesting. No invention or discovery is made without thought, though accident may suggest the thought; but here is an invention which, without any suggestion by accident, was evolved by laborious and long-continued thought, proceeding step by step to its conclusion. [5] I will mention here a contrivance that I once adopted for a small conservatory, which I wished to keep warm from the heat of a room to which it was adjoining. In each space of the window-frames were put two panes of glass, there being nearly half an inch of space between them. In this way I secured all the benefit of double windows with less expense and a less cumbrous arrangement. In mentioning this contrivance now and then, casually, I have found that a few others have thought of it, and adopted it with the same success that I did. [6] We are in entire ignorance of the nature of electricity, and we use the term _fluid_ merely as a matter of convenience. TRANSCRIBER'S NOTE Italic text is denoted by _underscores_. Bold text is denoted by =equal signs=. Obvious typographical errors and punctuation errors have been corrected after careful comparison with other occurrences within the text and consultation of external sources. Except for those changes noted below, all misspellings in the text, and inconsistent or archaic usage, have been retained. For example: farther, further; India rubber, India-rubber; every where; catechetical; incloses; tricksy; pervious; motal; enrobes; subtile.