SECTION 10.- EXPERIMENT AND USE OF INSTRUMENTS. 81 



extension of scientific observation, and constitutes really only 

 a refinement thereof. As a matter of fact, the more conclusive 

 kind of experiment is of recent origin, and many of the historic 

 truths have been reached by rough trials. Newton's investiga- 

 tions into the nature of light were not conducted by means of 

 elaborate apparatus. Franklin's kite or his pieces of variously 

 coloured cloths do not suggest modern experiments; and 

 Darwin's delightful study was anything but an up-to-date 

 laboratory. 



The special object of methodical experiment is to obtain 

 assured knowledge of quantity, properties, cause and effect, 



Chaldeans recorded an eclipse to the nearest hour, and the early Alexandrian 

 astronomers thought it superfluous to distinguish between the edge and 

 centre of the sun." (Jevons, Principles of Science, p. 271.) Psychologists 

 now resort to chronometers indicating the one-thousandth part of a second. 

 The best telescopes reveal a hundred million stars where sight disclosed 

 only about eight thousand, and where, with the aid of auxiliary photographic 

 processes, a thousand million may be registered. Spectrum analysis records 

 the 400-millionth of a grain. A good balance, containing in each pan about 

 a kilogramme, will indicate a difference of one-ten-thousandth of a grain. 

 The most efficient measuring machines will measure the millionth part of 

 an inch. There is literally no term to the refinement of instrumental 

 measurement. Where the unassisted eye detected a little over half a 

 dozen planets, five hundred are now known. With platinum resistance 

 thermometers "at ordinary temperatures the difference of temperature of 

 one-ten-thousandth of a degree can be deducted with moderate ease, while, 

 with great precautions, the hundred-thousandth of a degree can be esti- 

 mated". (Whetham, The Recent Development of Physical Science, 1906, 

 P- 71.) 



''Ordinary microscopical observation with the strongest lenses can show 

 particles of about 250 /m in diameter. We call particles of and above this 

 size microns. The ultramicroscope makes particles visible even down to 

 the size of 6 ,/', provided that the power of light applied is strong enough. 

 Such particles' are called submicrons." Those below this size are named 

 amicrons. (Frederick Czapek, Chemical Phenomena in Life, 1911, pp. 25-26.) 

 "Microtomes of the best workmanship have placed in the hands of histologists 

 the means of making serial sections of remarkable thinness and regularity." 

 (W. A. Locy, op. cit., p. 438.) "With our present instruments we can perceive 

 lines ruled on glass which are 1/90,000 of an inch apart. ... If ... we could 

 use the blue rays by themselves, their waves being much shorter, the limits 

 of possible visibility might be extended to 1 120,000." (C. S. Minot, The 

 Problem of Age, Growth, and Death, 1908, pp. 189-190.) 



"The number of rods and 'cones in the human eye is enormous. At a 

 moderate computation the cones may be estimated at over 3,000,000, and 

 the rods at 30,000,000. (Lord Avebury, On the Senses, Instincts, and Intelli- 

 gence of Animals, with special reference to Insects", p. 123.) "Though not 

 thicker than a sheet of thin paper, [the retina] consists of no less than nine 

 separate layers." (fbid., p. 122.) "According to the view of Helmholtz, the 

 smallest particle that could be distinctly defined, when associated with 

 others, is about 1 80,000th of an inch in diameter. Now, it has been estimated 

 that a particle of albumen of this size contains 125,000,000 of molecules. 

 In the case of such a simple compound as water, the number would be no 

 less than 8,000,000,000." (Ibid., p. 190.) 



"If we imagine a number of hydrogen molecules placed end to end, it 

 would require fifty millions of them to form a row one centimeter in length." 

 (W. C. McC. Lewis, "The Structure of Matter", in Science Progress, January, 

 1918, pp. 477-478.) 



6 



