274 HISTORY 01' STEAM. 



copper may be of very great length, for instance, many miles, and yet it 

 will produce the same effects at any part of it. 



If 26 magnetic needles, each bearing a letter of the alphabet, be fixed 

 in as many coils of 26 wires, then on passing the galvanism to any one or 

 other of these wires, the corresponding letter will be given as the sigpil, 

 and letters may be signalled in succession, so as to form complete words 

 and sentences. This is the elementary form of the apparatus described j 

 a French philosopher many years ago; and a similar imperfect apparatus 

 has recently been exhibiting publicly under a different name. The objec- 

 tions are the vibrations of the needles, and the loss of time and liability 

 to mistake, and also the length of space which the needles occupy, and 

 the not having them all at once under view ; besides the multiplicity of 

 wires, and the expence. The plan has of course been considered as no 

 way adapted for practice. 



Mr. Davy has, by the application of some not generally-known princi- 

 ples, brought the invention to the greatest perfection, as may be believed 

 from the following description ; Instead of 26 wires, Mr. Davy employs 

 only six ; and with these he can give upwards of 200 signals, including 

 the 26 letters of the alphabet. Nothing whatever is seen of magnetic 

 needles; there is a small dark screen, on which the letters (either singly, 

 or combined into words, or arbitraries) start into view the instant the key 

 at the opposite end is touched ; and this would be the case as instan- 

 taneously, even though the wires extended from London to Portsmouth 

 the length of distance, according to Mr. Davy's ^ 'an, making 

 absolutely no difference whatever. The coming of a cc.namunication 

 is always preceded by a sound or alarum ; and a bell, struck by the 

 action of a magnet, moved by electricity, separates the letters into words; 

 the bell being rung at any distance by the electricity. The readiness, 

 rapidity, and certainty of this apparatus surpasses all expectation. 



HISTORY OF STEAM. 



That power which can "engrave a seal and crush a mass of obdurate 

 metal like wax before it; draw out, without breaking, a thread as fine 

 as gossamer, and lift a ship of war, like a bubble in the air ; or 

 embroider muslin, forge anchors, cut steel in ribbands, and impel itself 

 against the opposition of the very tempest." 



One of the properties of heat is its power of expanding all bodies 

 into which it enters. Thus a piece of iron made red hot, will be found 



