XXxii LOGARITHMS. 



Example. Desired the colog of 306.2. Log 306.2 = 2.4860, colog = 3.5140. 



The use of cologs either with or without a table effects but small saving, 

 except in case a series of substitutions in a given formula are to be made, so 

 that a number of cologs may be looked out in immediate succession. 



Table of Cologs. The table of four-place cologarithms is arranged 

 similarly in every respect to the table of four-place logarithms, and 

 the cologs are taken from it just as logs from their table; noting, 

 however, that the cologs in the table have the characteristic I, and 

 that the differences are subtractive. 



Example. Desired the colog of 306.2. Separate into 3.062' lo 2 . 



In line 3.0, column 6, colog 3.06 =1.5143 



Difference from 



0.2 x ( 14) by difference table 3 colog 3.07 is 14. 



.*. colog 3.062 =7.5140 



colog lo 2 =2. 



. . colog 306.2 = colog 3.062- + colog lo 2 = 



Difference is - 6. 



Example. Desired the colog of o.oo 713 6. 



In line 7.1, column 3, is colog 7. 13 = 7.1469 



0.6 (6) by difference table = 4 



colog 7. 1 36 = 7.1465 



colog io~ 8 = + 3- 



colog o.oo 7136 = colog 7. 1 36 -f colog io~ 3 = 2.1465 



Habit in Reading off Numbers or Logarithms. Time can be econ- 

 omized, strain on the attention reduced, and liability to mistake 

 lessened by an easily acquired habit of grouping and emphasizing 

 the figures in reading off the numbers, the mantissa, and the num- 

 bers corresponding (antilogs) in using tables. 



A good method of reading is as follows : 



In reading a number or antilog pay no regard to the decimal 

 point. Emphasize the first figure; pause, read second and third 

 figures ; pause, read remaining figures in groups of three. Thus : 

 Desired the log of 30.62 047 2. Read this as 306 204 72, i.e. three 

 . . . naught six ... two naught four . . . seven two. 



In reading off a mantissa use no emphasis, but group the first 

 two figures together, and the subsequent figures by threes. Thus, the 

 mantissa .4869 would be read as 48 69, i.e. forty-eight . . . sixty- 

 nine; and .48601 as 48 601, i.e. forty-eight ... six naught one. 



In taking from the log table the numbers corresponding (antilog) 

 to .48601, it would be read 306 2, three . . . naught six ... two, 

 precisely as under the above rule for reading a number. 



