MICROSCOnC ADMEASUREMENT. 6 



experienced members, to state what the millemetre is. As the 

 Englishman deliglits in halving and quartering, so the Frenchman 

 drops naturally into decimals. The Paris metre is about 3 inches 

 more than an English yard, and this, divided into 100 parts, gives 

 centimetres, which are about equivalent to rather more than one- 

 third of an English inch, each centimetre again divided into tenths 

 gives millemetres, which are consequently the one-thousandth part 

 of a metre, or of 39 inches. This millemetre is (roughly) equal to 

 rather less than one-twenty-fifth of an English inch or x^ow ^^ 

 an inch, or, decimally expressed, .03937. The conversion therefore 

 of English into French or French into English measurements is 

 somewhat of a task, and liable to error. 



The only method which can be adopted, is to multiply our ex- 

 pression of a millimetre in decimal fractions of an inch, by the 

 decimals representing the French term under conversion ; thus — to 

 determine in English measurement 0.33 ^ m qj. _^^ ^f ^ mille- 

 metre, we must multiply .03937 by 0.33., which will give 



.03937 

 33 



11811 

 11811 



.0129921 of an inch. 



Taking care that there are as many decimal places to the right of 

 the point as the sum of the decimal places in both terms. 



It will be admitted that there is one plan, and one alone, which 

 is superior to the most facile mode of conversion — namely, the 

 adoption amongst all microscopists, both at home and abroad, of one 

 unit of measurement. The question to be discussed is, how can 

 this be attained ? I think the answer a simple one. We already 

 admit that the temis shoiild be expressed in decimals, for the old 

 plan of employing vulgar fractions, like other obsolete customs, 

 will soon become a matter of history. The only disputed point is 

 the unit, whether it shall be the inch or the millimetre, or yard and 

 metre, if you will ; for the yard is in reality our unit, of which the 

 inch is merely the twelfth of the third, as the metre is the miit of 

 Paris, save that we first divide it into three parts, and each into 



B 2 



