215 



SCIENTIFIC SIDE-LIGHTS 



Spoch 

 Srror 



snowy owl, who feeds on the ptarmigan, 

 may be said to illustrate deceptive colora- 

 tion. CHAPMAN Bird-Life, ch. 3, p. 44. (A., 

 1900.) 



1048. EQUIVALENCE OF FORCES 



Heat and Electricity. If I should set an 

 emery-wheel to revolving and hold a piece 

 of steel against it, the piece of steel would 

 become heated and incandescent particles 

 would fly off, making a brilliant display of 

 fireworks. The heat that has been developed 

 is the measure of the mechanical energy that 

 I have used against the emery-wheel. Now, 

 let us substitute for the emery-wheel another 

 wheel of the same size made of vulcanized 

 rubber, glass, or resin. I set it to revolving 

 at the same speed, and instead of the piece 

 of steel, I now hold a silk handkerchief or a 

 catskin against the wheel with the same 

 force that I did the steel. If now I provide 

 a Leyden jar and some points to gather up 

 the electricity that will be produced (instead 

 of the heat generated in the other case), it 

 would be found that the energy developed 

 in the one case would exactly balance that 

 of the other, if it were all gathered up and 

 put into work. The electricity stored in the 

 jar is in a state of strain, like a bent bow, 

 and will recoil, when it has a chance, with a 

 power commensurate with the time it has 

 been storing and the amount of energy used 

 in pressing against the wheel. If now I con- 

 nect my two hands, one with the inside and 

 the other with the outside of the jar, this 

 stored energy will strike me with a force 

 equal to all the energy I have previously 

 expended in pressing against the wheel, 

 minus the loss in heat. If I did it for a 

 long enough time this electrical spring 

 would be wound up to such a tension that 

 the recoil would destroy life if one put him- 

 self in the path of its discharge. ELISHA 

 GRAY Nature's Miracles, vol. iii, ch. 5, p. 44. 

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



1049. EROSION BY SAND-LADEN 



WATER Minute Particles Cut through Solid 

 Cliff Mighty Effect from Trivial Cause. 

 This power of erosion, so strikingly dis- 

 played when sand is urged by air, renders 

 us better able to conceive its action when 

 urged by water. The erosive power of a 

 river is vastly augmented by the solid mat- 

 ter carried along with it. Sand or pebbles, 

 caught in a river vortex, can wear away the 

 hardest rock ; " pot-holes " and deep cylin- 

 drical shafts being thus produced. An ex- 

 traordinary instance of this kind of erosion 

 is to be seen in the Val Tournanche, above 

 the village of this name. The gorge at Han- 

 deck has been thus cut out. TYNDALL Frag- 

 ments of Science, vol. i, ch. 7, p. 196. (A., 

 1900.) 



1050. ERROR, CUMULATIVE RE- 

 SULT OF Slight Inaccuracy Vitiates All Re- 

 sults in Space and Time. Our estimates of 

 the masses of the heavenly bodies also de- 

 pend upon a knowledge of the sun's distance 

 from the earth. The quantity of matter in 



a star or planet is determined by calcula- 

 tions whose fundamental data include the 

 distance between the investigated body and 

 some other body whose motion is controlled 

 or modified by it; and this distance gen- 

 erally enters into the computation by its 

 cube, so that any error in it involves a more 

 than threefold error in the resulting mass. 

 An uncertainty of one per cent, in the sun's 

 distance implies an uncertainty of more 

 than three per cent, in every celestial mass 

 and every cosmical force. 



Error in this fundamental element propa- 

 gates itself in time also, as well as in space 

 and mass. ... If, for instance, we 

 should find as the result of calculation with 

 the received data, that two millions of years 

 ago the eccentricity of the earth's orbit was 

 at a maximum, and the perihelion so placed 

 that the sun was nearest during the north- 

 ern winter (a condition of affairs which it 

 is thought would produce a glacial epoch in 

 the southern hemisphere), it might easily 

 happen that our results would be exactly 

 contrary to the truth, and that the state of 

 affairs indicated did not occur within ten 

 thousand years of the specified date and all 

 because in our calculation the sun's distance, 

 or the solar parallax by which it is meas- 

 ured, was assumed half of one per cent, too 

 great or too small. YOUNG The Sun, ch. 2, 

 p. 11. (A., 1898.) 



1051. ERROR, DEFINITE, MORE 

 HELPFUL THAN INDECISION -None of 



Bacon's aphorisms shows a clearer insight 

 into the relations between the human mind 

 and the external world than that which de- 

 clares ["Novum Organum," lib. ii, aph. 20], 

 " Truth to emerge sooner from error than 

 from confusion." A definite theory (even 

 if a false one) gives holding-ground ta 

 thought. Facts acquire a meaning with ref- 

 erence to it. It affords a motive for accu- 

 mulating them and a means of coordinating 

 them; it provides a framework for their ar- 

 rangement, and a receptacle for their pres- 

 ervation, until they become too strong and 

 numerous to be any longer included within 

 arbitrary limits, and shatter the vessel 

 originally framed to contain them. 



Such was the purpose subserved by Her- 

 schel's theory of the sun. It helped to- 

 clarify ideas on the subject. The turbid 

 sense of groping and viewless ignorance gave 

 place to the lucidity of a plausible scheme. 

 CLERKE History of Astronomy, pt. i, ch. 3, 

 p. 67. (Bl., 1893.) 



1052. ERROR, HONEST, LEADS TO 

 KNOWLEDGE Alchemists Discover Chem- 

 istry Atoms in Greek Philosophy. The 

 Greek philosophers expressed their ideas of 

 the states of matter by the four elements, 

 fire, air, water, earth; and they also had 

 learned or invented the doctrine of matter 

 being made up of atoms a principle now 

 more influential than ever in modern lec- 

 ture-rooms. The successors of the Greeks 

 were the Arabic alchemists, and their dis- 



