THE BIOLOGY OF DAILY LIFE. 73 



not speaking disrespectfully. I love the calc-spar. Cut 

 into the deft shapes of the Nicol's prisms, it forms 

 the ornament of my dearly-loved microscope, the 

 polariscope, and that is by virtue of this very property 

 of double refraction. I tried a very simple and foolish 

 experiment, you can do likewise. 



Instead of the single line, which will appear double 

 in the soberest of eyes take two figures writing them 

 very close together, thus : 12. Now look at them 

 through your spar, and by turning it round you can 

 have all the following varieties of configuration, 

 2211 ,21 , 21 , 21, 2211, and so on round the 



21 21 21 



whole circle. You see how your spar confounds the 

 decimal system. How, if applied to the addition of 

 money, it would make your pence to shillings, without 

 any regard to the values of the different vertical 

 columns viz., by " direct application" of one figure- 

 value to the other, without remembering or perceiving 

 the necessity of " carrying on" from one to the other, 

 according to the relative values. 



Instead of naming our columns units, tens, &c., or 

 pence and shillings, &c., let us call the first column 

 say " mechanical," the second " chemical," the third 

 ct biological," and so on. 



I can carry on my result, say from the chemical 

 into the biological column, and so long as I remember 

 the distinction, my work may be correct. But when 

 I use the mental calc-spar, I directly apply the 

 results of chemistry to biology, without noting this 

 distinction. 



Let (C) = 2 in chemical column, and (B) = 2 in 

 biological, let us assume that these two are related in 



