CHAPTER V. 



NUMBER-WORK IN NATURE-STUDY. 



It is the function of observation to define a mental picture or 

 image. By means of number the image is defined through a deter- 

 mination of quantity. In the appHcation of number therefore, the 

 same principles must be observed that are employed in defining the 

 image by other means. 



1. There must he a clear idea concerning the image to he defined. 

 — If, for example, a pupil is required to find the number of barrels 

 of water in the rainfall of a given area, he should know beforehand 

 how this result is to contribute to the nature-image that is being 

 developed. The life-conditions of a given area are largely affected 

 by the rainfall. By finding the quantity the student determines 

 exactly the value of that particular factor, which enables him to 

 make definite comparisons with other areas, or with the same area 

 in different months or years. 



2. There must he an appropriate selection of units of measure- 

 ment. — The units chosen must be such as will involve the pupils 

 least in the details of process, and which, at the same time, will 

 best approximately define the image. 



Pupils in the early grades should deal with quantities of large 

 amount. For example, the amount of water in the soil found by 

 drying out one cubic inch might serve the purpose with an adult, 

 but it would make practically no impression on young children; 

 whereas the picture might be made very interesting if in the latter 

 case a bucketful of soil were used. The bucketful would be, perhaps, 

 as much as the pupil could lift, and might weigh ten pounds. It 

 would be much easier to get numerical results that would be intel- 

 ligible if pounds were used, than it would be if ounces were 

 employed. So, too, yards in many cases would mean more than 

 feet or inches. 



3. The most expeditious methods of measurement should he 

 adopted. — Estimate, then measure. Neglect the fractions that do 

 not stand for an actual image in the pupil's mind. This will fix 

 naturally the limits of the decimal. If a hundredth of a pint 



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