Measurement of Length 7 



the eye must also be vertically over point B. In the 

 figure it will be seen that B lies between the 3rd 

 and 4th inch marks, and also between the 7th and 

 8th marks (counting from the figure 3) which divide 

 the 4th inch into 10 equal parts. That is to say, 

 the distance from A to B (or, as it is frequently 

 termed, the distance AB) is between 3 T 7 ^ (3- 7) and 

 3 T 8 Q (3- 8) inches. Let us now imagine the distance 

 between the 7th and 8th subdivisions to be further 

 divided into 10 equal parts. Each of these imaginary 

 parts would be -^ of T ^, or T ^ inch. From the 7th 

 mark to where the point B touches the edge of the 

 scale, we should estimate to be about four of our imagi- 

 nary TI L inch divisions. This amount must be added to 

 3 T 7 inches. Hence the reading on the scale at B, and 

 therefore the total distance from A to B, is 

 3 i 7 o + TW = 3 iw (3* 74) inches. 



To verify this result a second determination of the 

 distance from A to B should be made thus : place the 

 scale so that the mark numbered " 1 " is at A, adjust 

 till B is on the edge of the scale, take the reading on 

 the scale at B, and subtract one inch from this reading. 

 A third measurement should also be made by placing 

 the zero of the scale at B, and reading off the measure- 

 ment at A. 



Repeat the above measurements, using the edge of 

 the scale divided into centimetres, estimating parts of 

 a millimetre by the method given for estimating a 

 fraction of an inch less than -^ inch. 



Tabulate your results, and find the mean (or 

 average) value for the length AB in inches by dividing 

 the sum of the three measurements obtained by the 

 number of measurements made. Similarly find the 

 mean value of the length of AB in centimetres. 



