148 REMINISCENCES. 



great accuracy in most of his measurements, and had not 

 good scales ; he had an old three-foot rule, which was the 

 common property of the household, and was constantly being 

 borrowed, because it was the only one which was certain to 

 be in its place unless, indeed, the last borrower had forgotten 

 to put it back. For measuring the height of plants, he had 

 a seven-foot deal rod, graduated by the village carpenter. 

 Latterly he took to using paper scales graduated to milli- 

 meters. For small objects he used a pair of compasses and 

 an ivory protractor. It was characteristic of him that he took 

 scrupulous pains in making measurements with his somewhat 

 rough scales. A trifling example of his faith in authority 

 is that he took his " inch in terms of millimeters " from an old 

 book, in which it turned out to be inaccurately given. He 

 had a chemical balance which dated from the days when he 

 worked at chemistry with his brother Erasmus. Measure- 

 ments of capacity were made with an apothecary's measuring 

 glass : I remember well its rough look and bad graduation. 

 With this, too, I remember the great care he took in getting 

 the fluid-line on to the graduation. I do not mean by this 

 account of his instruments that any of his experiments suffered 

 from want of accuracy in measurement, I give them as 

 examples of his simple methods and faith in others faith at 

 least in instrument-makers, whose whole trade was a mystery 

 to him. 



A few of his mental characteristics, bearing especially on 

 his mode of working, occur to me. There was one quality of 

 mind which seemed to be of special and extreme advantage 

 in leading him to make discoveries. It was the power of never 

 letting exceptions pass unnoticed. Everybody notices a fact 

 as an exception when it is striking or frequent, but he had a 

 special instinct for arresting an exception. A point appa- 

 rently slight and unconnected with his present work is passed 

 over by many a man almost unconsciously with some half- 

 considered explanation, which is in fact no explanation. It 



