LESSONS IN ELECTRICITY. 



289 



dency of the human mind, not to rest 

 satisfied with the facts of observation, but 

 to pass beyond the facts to their invisible 

 causes. 



Dr. Wall (1708) experimented with 

 large, elongated pieces of amber. lie 

 found wool to be the best rubber of am- 

 ber. " A prodigious number of little 

 cracklings" was produced by the fric- 

 tion, every one of them beinjj accom- 

 panied by a flash of light. " This light 

 and crackling," says Dr. Wall, " seem 

 in some degree to represent thunder and 

 lightning." This is the first published 

 allusion to thunder and lightning in con- 

 nection with electricity. 



Stephen Gray (1729) also observed the 

 electric brush, {-mappings, and sparks. 

 He made the prophetic remark that 

 " though these effects are at present only 

 minute, it is probable that in time theie 

 may be found out a way to collect a 

 greater quantity of the electric fire, and, 

 consequently, to increase the force of 

 that power which by several of those ex- 

 periments, if we are permitted to com- 

 p'-irc great things with small, seems to be 

 of the same nature with that of thiindcF 

 and lightning." This, you will ob- 

 serve, is far more definite than the re- 

 mark of Dr. Wall. 



3. The Art of Experiment. 



We have thus broken ground with a 

 few historic notes, intended to show the 

 gradual growth of electrical science. Our 

 next step must be to get some knowledge 

 of the facts referred to, and to learn how 

 they may be produced and extended. 

 The art of producing and extending such 

 facts, and of inquiring into thorn by prop- 

 er instruments, is the art of experiment. 

 It is an art of extreme importance, for 

 by its means we can, as it were, converse 

 with Nature, asking her questions and 

 receiving from her replies. 



It was the neglect of experiment, and 

 of the reasoning based upon it, which 

 kept the knowledge of the ancient world 

 confined to the single fact of attraction 

 by amber for more than 2000 years. 



Skill in the art of experimenting docs 

 not come of itself ; it is only to be ac- 

 quired by labor. When you first take a 

 billiard cue in your hand, your strokes 

 are awkward and ill-directed. When 



you learn to dance, your first movements 

 are neither graceful nor pleasant. By 

 practice alone, you learn to dance and 

 to play. This also is the only way of 

 learning the art of experiment. You 

 must not, therefore, be daunted by your 

 clumsiness at first : you must overcome 

 it, and acquire skill in tho art by repeti- 

 tion. 



In this way you will come into direct 

 contact with natural truth you will 

 think and reason not on what has been 

 said to you in books, but on \rhat has 

 been said to you by Nature. Thought 

 springing from this source has a vitality 

 not derivable from mere book-knowledge. 



4. Materials for Experiment. 



At this stage of our labors wo arc to 

 provide ourselves with the fallowing 

 materials : 



FIG. 1. 



a. Some sticks of sealing-wax ; 



5. Two pieces of gutta-percha tubing, 

 about 18 inches long and f of an inct 

 outside diameter ; 



c. Two or three glass tubes, about 18 

 inches long and f of an inch wide, closed 

 at one end, and not too thin, lest they 

 should break in your hand and cut it ; 



d. Two or three pieces of clean flannel, 

 capable of being folded into pads of two 

 ar three layers, about eight or ten inches 

 square ; 



