198 



SCIENCE. 



AN INVESTIGATION OF THE VIBRATIONS OF 

 PLATES VIBRATED AT THE CENTRE. 



By Professor Thomas R. Baker. 



Since the publication of the paper under the above head- 

 ing we have received from Professor Baker two drawings 

 illustrating the same, which we now produce. 



The first, Fig. 1, shows Professor Baker's method of pro- 

 ducing the sand pictures, useful for class illustration : 



Fie. 1. 



Most of the plates used were window panes of various 

 shapes and sizes, they were vibrated by rubbing an attached 

 glass rod. The tubes, which were about -fc of an inch in 

 diameter and 20 inches long, were attached at right angles 

 to the face of the plate with sealing wax. The support for 

 the plate was a rubber cap, the common lead pencil eraser, 

 fitted on the end of a post projecting from a disk of lead. 

 A short rubber-capped lead pencil fixed upright in a 

 wooden block answers the purpose just as well. 



The plate was balanced on the support, the tube stand- 

 ing upright, and held loosely between the thumb and fore- 

 finger of the left hand. Then catching the tube between 

 the moistened thumb and forefinger of the right hand and 

 rubbing downward the vibrations of the plate were pro- 

 duced. 



Fig. 2 represents copies of various sand pictures thus 

 produced. I le states : 



" The figures were copied by placing the plate over paper 

 wliicli had been wel with a solution of potassium bichro- 

 mate and dried in the dark. The plate and paper were ex- 

 posed to diffused light, or to the vertical rays of the sun. 

 I h<- paper not hid by the sand soon darkened, and when 

 this change had taken place the plate wasre moved and a 



lead pencil run along the bands of lighter colored paper 

 representing the sand lines. This paper was then placed 

 on white paper, and the figures copied by pressure. 

 About 150 sand-figures were copied and traced." 



For a summary of the facts derived from these experi- 

 ments we refer our readers to Science, Vol. I., No. 13, 

 September 25th, 1880, page 157. 



FIELD WORK BY AMATEURS.* 

 By Helen Harelin Walworth. 



It is announced, I believe, that one of the aims of the 

 American Association for the Advancement of Science is 

 to make Natural Science popnlar, to encourage its pursuit 

 among all classes of people. It is because I have such an 

 understanding of its aims that I presume to speak a word 

 in behalf of the class who love science, yet can give to it 

 but a limited portion of their time and thoughts. 



Such a class of persons are important factors in the de- 

 velopment of every department of knowledge and art. The 

 professor, the artist, the specialist may have higher aims ; 

 they certainly do more thorough work, yet they would 

 scarcely be understood, appreciated and encouraged if there 

 did not exist the intermediate class who admire, applaud 

 and exhibit the work they cannot themselves perform. 



I therefore deprecate the scorn with which the profes- 

 sional too often contemplates the dabbler in his specialty, 

 as he will perhaps designate the amateur. " A little knowl- 

 edge is a dangerous thing" only when it is pretentious. A 

 mere elementary knowledge of any natural science is a 

 proposition from which reason starts ; it is a foundation on 

 which thought builds, and a height from which imagination 

 takes its flight. It is an education in all other knowledge, 

 because it demands attention, observation and accuracy 

 with well-defined expression. 



How can the popular interest in science be stimulated 

 and increased? A majority of educated people shrink with 

 aversion from the memory ol tasks performed at school. 

 The bare mention of a natural science recalls pages of un- 

 pronounceable words and incomprehensible classifications. 

 Yet, if a practical geologist or botanist will take any three 

 of these individuals into the field with him and beguile them 

 into breaking rocks or gathering flowers scientifically, two 

 out of every three will be delighted with the occupation, 

 and will strive to recall the classical names which inspired 

 them with disgust while they were merely theoretical. It 

 is then only while science is an abstraction that it repels; 

 render it practical and it invariably attracts. 



In every city and village of our country wc find numerous 

 clubs and societies devoted to special objects of literature 

 and art, and a few to science. These last are rare, they 

 would be numerous and active if slight encouragement were 

 given to them by those who have the ability to guide and di- 

 rect. Such clubs and associations should begin with a 

 short and well directed course of reading, accompanied, if 

 possible, by a few interesting lectures as a preparation for 

 field work which should not be delayed through timidity or 

 a feeling of ignorance. A few visits to the field by a geologi- 

 cal club will serve to arouse enthusiasm, and inspire a de- 

 sire for research, which months of reading would not ac- 

 complish. It cannot be urged that many live in localities 

 where there is nothing to study, for I believe it maybe safely 

 stated that uninvestigated scientific facts lie over and under 

 every square mile of the United States. Yet I have heard 

 the members of a geological club, who studied exclusively 

 in the class-room, make such a plea. When visiting their 

 city I said to one of them, " What rocks have you in this 

 vicinity?" The person addressed looked at me with un- 

 qualified surprise and answered, " We have none." lex- 

 claimed, "you have a river and hills, and many rail road 

 cuttings, the foundation of things must be visible some- 

 where." But this individual insisted that there was abso- 

 lutely nothing to examine within walking or driving distance 

 of that city. There is, of course, a difference in varying 

 localities. In Davenport, Iowa, where there is now a well- 

 established Academy of Science, located in its own line 

 building, and displaying a great museum, a few years ago 

 there were but half a do/en persons who met in a hired 



♦Read before the A. A. A. S., Boston, 1880. 



