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 : 
Fig. i. 
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 -pg 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. 
Fig. 2 represents copies of various sand pictures thus 
produced. He states : 
“ The figures were copied by placing the plate over paper 
which had been wet 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. 
The 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 of 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 we 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, b)' 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 railroad 
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 fine 
building, and displaying a great museum, a few years ago 
there were but half a dozen persons who met in a hired 
♦Read before the A. A. A. S., Boston, t88o. 
