34 SCIENTIST 



he simply gets confused. Much of science began merely 

 as an attempt to describe the physical world as it stands. 

 It was perfectly natural to set about such descriptions 

 one bit at a time. An obvious next step was to pull things 

 apart and describe the constituent parts. Physics passed its 

 simple descriptive phase some time ago; chemistry still 

 devotes considerable effort to describing new compounds 

 in terms of color, weight, form, melting point, and so on. 

 Biology enjoyed a very long and important descriptive 

 phase, partly because of the very richness of the world of 

 living things. There simply are a great many things to 

 dissect and describe. 



The next stage was to describe changes in a single thing 

 or in a group of things over time. For example, the early 

 astronomers noticed at once that the stars changed their 

 positions during the night and from night to night during 

 the year in a regular way while the planets followed much 

 more complex paths. Such motions could be noted and 

 set down one at a time and later put together on charts 

 and in mathematical formulas to provide some idea of how 

 the solar system works. 



Somewhat later, science began to encounter situations 

 in which it was not nearly so obvious how to go about 

 observing the bits and pieces in isolation from one another. 

 The attempt to break down relatively complex systems 

 into appropriate constituents for purposes of observation 

 led to the development of the so-called controlled experi- 

 ment. Although examples of controlled observation can be 

 found in ancient and medieval times, the great develop- 

 ment of the method may reasonably be said to have begun 

 with Galileo. More than any other single factor, it is respon- 

 sible for the remarkable development of modern science 

 in the last four centuries. 



To illustrate what we mean by the controlled experi- 



