627 



SCIENTIFIC SIDE-LIGHTS 



Shore 



Similarity 



ant flash of intelligence and glow of joy"; 

 she seemed suddenly to become aware of the 

 general purpose embedded in the different 

 details of all these signs, and from that mo- 

 ment her education went on with extreme 

 rapidity. JAMES Psychology, vol. ii, ch. 22, 

 p. 358. (H. H. & Co., 1899.) 



3 1 05. SILENCE IN VACUUM Sound 

 Demands a Medium. Sound cannot be 

 transmitted through a vacuum, as shown by 

 the following familiar experiment made by a 



Philosopher named Hawksbee as far back as 

 705. Place a bell that is operated by a 

 clock-work inside of the receiver of an air- 

 pump. This receiver is a large bell glass, 

 ground to make an air-tight fit on the bed- 

 plate of the air-pump. Suspend the bell 

 inside the receiver, by some kind of cord 

 that will not transmit sound, and then set 

 it to ringing. At first it will ring as loudly 

 as tho it were in the open air. Now, work 

 the pump and exhaust the air. The sound 

 will grow fainter until a nearly perfect 

 vacuum is obtained, when the sound will 

 cease, altho the hammer is still striking the 

 bell the same as at first. Now let the air in 

 and the ringing is heard again. ELISHA 

 GRAY Nature's Miracles, vol. ii, ch. 6, p. 62. 

 (F. H. & H., 1900.) 



3 1 06. SILENCE PRODUCED BY IN- 

 TERFERING SOUNDS Analogies of Sound 

 and Light Darkness Produced by Adding 

 Light to Light. Thomas Young's funda- 

 mental discovery in optics was that the 

 principle of interference was applicable to 

 light. Long prior to his time an Italian 

 philosopher, Grimaldi, had stated that under 

 certain circumstances two thin beams of 

 light, each of which, acting singly, produced 

 a luminous spot upon a white wall, when 

 caused to act together, partially quenched 

 each other and darkened the spot. This was 

 a statement of fundamental significance, but 

 it required the discoveries and the genius of 

 Young to give it meaning. How he did so 

 will gradually become clear to you. You 

 know that air is compressible; that by 

 pressure it can be rendered more dense, and 

 that by dilation it can be rendered more 

 rare. Properly agitated, a tuning-fork now 

 sounds in a manner audible to you all, and 

 most of you know that the air through 

 which the sound is passing is parceled out 

 into spaces in which the air is condensed, 

 followed by other spaces in which the air is 

 rarefied. These condensations and rarefac- 

 tions constitute what we call waves of 

 sound. You can imagine the air of a room 

 traversed by a series of such waves, and 

 you can imagine a second series sent through 

 the same air, and so related to the first that 

 condensation coincides with condensation 

 and rarefaction with rarefaction. The con- 

 sequence of this coincidence would be a 

 louder sound than that produced by either 

 system of waves taken singly. But you can 

 also imagine a state of things where the 

 condensations of the one system fall upon 



the rarefactions of the other system. In 

 this case the two systems would completely 

 neutralize each other. Each of them taken 

 singly produces sound; both of them taken 

 together produce no sound. Thus, by adding 

 sound to sound we produce silence, as Gri- 

 maldi in his experiment produced darkness 

 by adding light to light. TYNDALL Lectures 

 on Light, lect. 2, p. 57. (A., 1898.) 



3107. SIMILARITY, ASSOCIATION 



BY At the, Foundation of Reasoning. After 

 the few most powerful practical and esthet- 

 ic interests, our chief help towards notic- 

 ing those special characters of phenomena 

 which, when once possessed and named, are 

 used as reasons, class names, essences, or 

 middle terms, is this association by simi- 

 larity. Without it, indeed, the deliberate 

 procedure of the scientific man would be im- 

 possible; he could never collect his analo- 

 gous instances. But it operates of itself in 

 highly gifted minds without any delibera- 

 tion, spontaneously collecting analogous in- 

 stances, uniting in a moment what in Nature 

 the whole breadth of space and time keeps 

 separate, and so permitting a perception of 

 identical points in the midst of different cir- 

 cumstances, which minds governed wholly 

 by the law of contiguity could never begin 

 to attain. JAMES Psychology, vol. ii, ch. 

 22, p. 347. (H. H. & Co., 1899.) 



3108. SIMILARITY OF INVENTIONS 



How Far Denoting Unity of Race. It is 

 agreed, then, by all that certain kinds of 

 similarity may exist in regions wide apart 

 independently when the occasion arises and 

 the environment permits. It is also ad- 

 mitted that things may be so similar as to 

 allow no doubt that they were created under 

 the inspiration of the same teachers. There 

 is, then, a criterion, a boundary line, not 

 definitely fixed, perhaps, but a fence between 

 those so-called similarities that arise inde- 

 pendently and those which show accultura- 

 tion of some kind. This fence must be 

 largely psychological. 



The question, I repeat, is not one of 

 origins at all, but one of the number, kinds, 

 and degrees of similarities in the artificiali- 

 ties of life. For example, the invention of 

 the canoe is a natural, human process; the 

 bark canoe is environmental, the birch-bark 

 canoe is culture-historical. But what should 

 we say of the Amur and the Columbia River 

 types, each pointed beneath the water like 

 a monitor and unlike any other species? 

 Surely these must have some kind of accul- 

 turation. Now, if it be found that the 

 Columbia stock and the Amur people have 

 also the same name for their pointed canoes, 

 and a multitude of other coordinated like- 

 nesses, then kinship of blood or nationality 

 is proclaimed. MASON Similarities in Cul- 

 ture, from the American Anthropologist, 

 vol. viii, p. 115. 



31O9. SIMILARITY THE FOUNDA- 

 TION OF SCIENCE, AS OF WIT Genius 

 Involves Hard Work. The first discovery of 



