226 SECTION MECHANICS. 



\ve have had the advantage of hearing three gentlemen on this subject, 

 who rank first as authorities. I think M. Tresca puts it very fairly, 

 that both methods have their advantages. The measurement a but, 

 as we have seen it explained by Sir Joseph Whitworth, seems to me 

 most adapted to the determination of very slight differences of linear 

 measure, provided the piece of substance measured is short, as is the 

 case in measuring thickness, whereas for the measurement of long 

 articles, the other method seems to possess advantages of its own. 

 Sir Joseph Whitworth will say a few words in reply to what has been 

 advanced, and then I am afraid we shall have to close this discussion, 

 as we have a great deal of business on hand. 



Sir JOSEPH WHITWORTH : I will just say that the line-measure 

 previous to 1851, had engaged the attention of a number of gentlemen 

 the Reverend Mr. Sheepshanks being one who were appointed the 

 Commission, and were engaged for several years upon it. They had 

 rooms in Somerset House, and were going to get an Act of Parliament 

 for these standards which they recommended. The original standard 

 as was observed by Mr. Chisholm had been destroyed when the Houses 

 of Parliament had been burned down. In the meantime I was making 

 my experiments on end-measure, and I exhibited at the Exhibition of 

 1851 a standard yard measure, and showed there, that the differences 

 in length by small increments of heat was very great. In the machine 

 that I exhibited, which was the standard yard, I showed repeatedly 

 that when the feeling-piece at the end was adjusted, you could not 

 touch the bar with your finggr_jiaij, without the feeling-piece 

 being suspended. You can make, of course, any number of 

 standards, and supposing we had a room at the temperature of the 

 human body, we could then handle these things ; but the commission 

 determined that the degree of heat should be 62 Fahrenheit, and of 

 course you cannot touch anything with your hands without making it 

 longer. The way in which I supported the standard yard was objected 

 to before this commission, and it was said, it was better to support it 

 on rollers, but I may say that the gentlemen who were engaged in 

 determining what the standard yard should be, though they were 

 scientific gentlemen of the greatest eminence, did not know how to use 

 their hands. They recommended that the standard inch, which I con- 

 sidered was very important, should be our end-measure, and also the 



